The Wireless Communications Professional..A Guide For Engineers And Managers

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The Complete Wireless
Communications Professional:
A Guide for Engineers and Managers
The Complete Wireless
Communications Professional:
A Guide for Engineers and Managers
William Webb
Artech House
Boston • London
Library of Congress Cataloging-in-Publication Data
Webb, William, 1967–
The complete wireless communications professional : a guide for engineers
and managers / William Webb
p. cm. — (Artech House mobile communications library)
Includes bibliographical references and index.
ISBN 0-89006-338-9 (alk. paper)
1. Wireless communication systems. 2. Mobile communication systems.
I. Title. II. Series.
TK5103.2.W42 1999
621.6845—dc21 98-51802
CIP
British Library Cataloguing in Publication Data
Webb, William, 1967–
The complete wireless communications professional : a guide for engineers
and managers—(Artech House mobile communications library)
1. Wireless communication systems.
I. Title
621.3’82
ISBN 0-89006-338-9
Cover design by Lynda Fishbourne
© 1999 ARTECH HOUSE, INC.
685 Canton Street
Norwood, MA 02062
All rights reserved. Printed and bound in the United States of America. No part of
this book may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying, recording, or by any information storage and
retrieval system, without permission in writing from the publisher.
All terms mentioned in this book that are known to be trademarks or service
marks have been appropriately capitalized. Artech House cannot attest to the accu-
racy of this information. Use of a term in this book should not be regarded as
affecting the validity of any trademark or service mark.
International Standard Book Number: 0-89006-338-9
Library of Congress Catalog Card Number: 98-51802
10987654321
Contents
Preface What is a complete wireless professional? xiii
Introduction xiii
Format of this book xiv
Acknowledgments xv
Part I Introductory material 1
1Some interesting history 3
1.1 Introduction 3
1.2 Early history 4
1.3 Some key milestones in mobile radio history 8
1.4 Recent history 10
References 16
Part II Mobile radio systems 17
2The basics of mobile radio 19
2.1 Introduction 19
v
2.2 Basic principles of propagation 20
2.3 Radio spectrum utilization 32
2.4 Basic system design 37
2.4.1 System overview 37
2.4.2 Voice encoding 37
2.4.3 Secure transmission 46
2.4.4 Overcoming channel imperfections 48
2.4.5 Frequency and phase modulation 55
2.4.6 Clock recovery 64
2.4.7 Carrier recovery 66
2.4.8 Multiple access 68
2.5 Packet and circuit transmission 79
2.6 Theoretical capacity of mobile radio systems 80
References 82
Further reading 83
3Cellular radio technologies 85
3.1 The range of cellular systems 85
3.2 GSM 88
3.2.1 System architecture 88
3.2.2 Locating a subscriber and starting calls 91
3.2.3 Transmission within GSM 93
3.3 cdmaOne 101
3.4 Other systems 106
References 106
4Private mobile radio systems 107
4.1 Introduction 107
4.2 Simple private radio systems 114
vi The Complete Wireless Communications Professional
4.3 TETRA 119
4.3.1 Introduction 119
4.3.2 System operation 120
4.3.3 Technical parameters 123
4.4 Other systems 125
References 125
5Other mobile radio systems 127
5.1 Introduction 127
5.2 Cordless systems 128
5.2.1 Overview of cordless telephony 128
5.2.2 Digital enhanced cordless telephone 130
5.2.3 Personal handiphone system 134
5.3 Wireless local loop systems 135
5.3.1 Introduction to wireless local loop 135
5.3.2 Access technologies: radio and cable 137
5.3.3 WLL and cellular: the differences 142
5.3.4 Technologies for WLL and LMDS/MVDS 144
5.4 Satellite systems for telephony 149
5.4.1 Introduction 149
5.4.2 Concept 150
5.4.3 Economics of satellite systems 153
5.5 TV, radio, and other systems 154
References 159
6Interfacing with fixed networks 161
6.1 The need for fixed networks 161
6.2 Fixed network architectures 162
6.3 Fixed network protocols 170
Contents vii
6.4 Fixed mobile convergence 178
6.4.1 Introduction 178
6.4.2 Defining fixed-mobile convergence 179
6.4.3 Possible solutions 179
6.4.4 The future of the FMC marketplace 185
References 187
Part III The mobile network operator 189
7Designing a mobile radio network 191
7.1 Technical design 191
7.1.1 Introduction 191
7.1.2 Network planning 193
7.1.3 Radio planning 196
7.1.4 Microcells and picocells 198
7.1.5 Interconnection 199
7.1.6 Operations and maintenance planning 203
7.1.7 Supplier selection 204
7.1.8 Network deployment 205
7.2 Applying for a license 205
7.3 The mobile radio equipment manufacturer 208
References 210
8Economics of a mobile radio network 211
8.1 Understanding financial information 211
8.1.1 Introduction to accounting 211
8.1.2 The profit and loss account 212
8.1.3 The balance sheet 215
8.1.4 The funds flow statement 218
8.1.5 Performing first pass modeling 221
viii The Complete Wireless Communications Professional
8.2 The business case 223
8.2.1 The overall structure of the business case 223
8.2.2 The network costs 223
8.2.3 The operating expenses 227
8.2.4 Revenue 227
8.2.5 Financing 233
8.2.6 Summary 235
References 238
9Operating a mobile radio network 239
9.1 Introduction 239
9.2 Monitoring the network 240
9.3 Tariff policies and their implications 244
9.4 Capacity enhancement 246
9.4.1 Introduction 246
9.4.2 The available capacity enhancement techniques 246
9.4.3 Dual-band operation 247
9.4.4 Techniques affecting the cluster size 247
9.4.5 Using more cells 251
9.4.6 Which capacity enhancement techniques should be
used when? 252
10 Large users of mobile radio networks 255
10.1 Introduction 255
10.2 Railways 257
10.2.1 Introduction 257
10.2.2 Current railway communications within Europe 258
10.2.3 Railway requirements 259
10.2.4 PMR versus cellular 261
Contents ix
10.3 Police 263
10.3.1 Introduction 263
10.3.2 Description of requirements 264
10.3.3 Selection of radio system 265
10.4 Other emergency services 266
10.5 Other users 267
11 Future mobile radio systems 269
11.1 Progress in radio systems 269
11.2 The third generation vision 270
11.3 Designing the third generation system 274
References 277
Part IV Regulators and governments 279
12 Radio spectrum 281
12.1 Introduction 281
12.2 The management of radio spectrum 282
12.3 Modern allocation and assignment methods 287
12.4 Implications for the mobile radio operator 290
12.5 Government policy 294
References 297
13 Standardization 299
13.1 Introduction 299
13.2 Standards-making bodies 300
13.3 Writing standards 304
References 307
xThe Complete Wireless Communications Professional
Part V Becoming a better wireless professional 309
14 Areas of conflict 311
14.1 Introduction 311
14.2 TETRA versus GSM 313
14.2.1 Background to the debate 313
14.2.2 Evaluation of the technologies 313
14.2.3 Economic comparison 315
14.2.4 Analyzing the debate 318
14.3 DECT versus PHS 319
14.3.1 Background to the debate 319
14.3.2 The key issues 319
14.3.3 Analyzing the debate 321
14.4 CDMA versus TDMA 322
14.4.1 Background to the debate 322
14.4.2 The capacity of CDMA versus TDMA 323
14.4.3 Other issues introduced into the debate 325
14.4.4 Analyzing the debate 327
14.5 Handling conflict 327
References 328
15 Management 329
15.1 Introduction 329
15.2 An overview of management 330
15.3 Understanding corporate strategy 332
References 338
16 The complete wireless professional 339
16.1 Introduction 339
Contents xi
16.2 Conferences and publications 340
16.3 Links with research organizations 346
16.4 Qualifications 349
References 350
Appendix A Erlang B macro 351
Appendix B Mandating standards 353
B.1 Introduction 353
B.2 The key issues 354
B.3 Case studies 359
B.4 Implications 361
B.5 Conclusions 362
References 363
Glossary 365
About the author 385
Index 387
xii The Complete Wireless Communications Professional
Preface
What is a complete wireless
professional?
Since we cannot know all that is to be known of everything, we ought to
know a little about everything.
Blaise Pascal (1623–1662)
Introduction
When thinking about mobile radio engineers there is a tendency to
assume that the engineering function relates solely to the technical
aspects of the network, such as the equipment design or the network
design. That is certainly a key part of the role of a mobile radio engineer.
However, increasingly engineers are required to interact with profession-
als from other divisions. The “complete wireless professional” should
know about mobile networks; fixed networks; other types of mobile
systems; regulatory and government policy; the requirements of the
users; and financial, legal, and marketing issues. Otherwise, there is a
tendency for the engineering, finance, and marketing departments to be
xiii
completely separate entities that are unable to communicate accurately
with each other. The net result is products that do not fit the marketing
requirements or are not financially viable, although they may be master-
pieces of advanced engineering design.
This book looks at the range of topics that complete wireless commu-
nications professionals need to understand in order to perform their task
well. Clearly, above all else, they need to have an engineering knowledge
of how mobile radio systems work. Such a body of knowledge is con-
tained in many excellent text books and reference works; the intention
here is to provide the salient points in each area and a guide to further
reading. In other areas such as finance, the complete wireless professional
only requires an understanding of the key issues, and the brief description
provided in this book may be sufficient.
To some extent, this book gathers reference material from a wide
range of technical, managerial, and financial sources and represents in
summary form those issues that are key to the complete wireless profes-
sional. By encompassing the information in a suitable framework and
providing additional chapters on areas such as the resolution of conflicts
and career structure, it is hoped that the effect of the whole is greater than
the sum of its parts.
Above all, complete wireless professionals need to understand the
world around them and apply this knowledge to engineering issues. This
book describes the world of mobile radio.
Format of this book
This book is divided into five parts.
◗This first part provides introductory material in the form of a chap-
ter discussing the relevant history of mobile communications.
◗The second part looks at mobile radio systems, considering the
basics of mobile radio, the design of cellular and private radio sys-
tems, and the issues concerned with interworking with the fixed
network.
◗The third part looks at the role of a mobile radio operator and dis-
cusses the design of mobile radio networks, the operation of these
xiv The Complete Wireless Communications Professional
networks, the needs of large user groups, and the future of mobile
radio systems.
◗The fourth part looks at the regulatory and government decisions
that impact mobile radio, including the management of radio spec-
trum, the standardization of mobile radio systems, and the effect of
government policy on the mobile radio community.
◗The final part focuses on becoming a better engineer by considering
the resolution of conflicts such as the time division/code division multiple
access (TDMA/CDMA) debate, on the need for understanding mana-
gerial issues, and finally on the way to become a complete wireless
professional through professional vehicles and career structure.
Acknowledgments
In writing this book, I drew upon all my experience gained over years in
the industry. I have learned something from almost everyone with whom
I have come into contact and thank all of those with whom I have had dis-
cussions. Special thanks are due to a number of key individuals. During
my time at Multiple Access Communications, Professor Ray Steele, Pro-
fessor Lajos Hanzo, Dr. Ian Wassell, and Dr. John Williams, among others,
taught me much about the workings of mobile radio systems. At Smith
System Engineering, Richard Shenton, Dr. Glyn Carter, and Mike Shan-
non provided valuable knowledge, as have contacts with a number of
others in the industry, including Michel Mouly (Independent Consult-
ant), Dirk Munning (DeTeCon), Michael Roberts (Alcatel), Mike Watkins
and Les Giles (Racal-BRT), Mike Goddard and Jim Norton (Radiocommu-
nications Agency), and Phillipa Marks (NERA). At NetCom Consultants,
Steve Woodhouse, Don Pearce, Mark Cornish, and others taught me
about WLL and cellular operators. While at Motorola, Raghu Rau has
provided invaluable guidance. Many presentations and papers from those
involved in the mobile radio industry contributed to my understanding.
Most importantly, my wife, Alison, has persevered as I worked many eve-
nings and spent much time away from home in my quest to absorb
knowledge in as many spheres as possible, to gain additional qualifica-
tions, and to try to become a complete wireless communications profes-
sional myself.
Preface xv
Introductory
material
I
PART
Some interesting
history
When I want to understand what is happen-
ing today, or to try and decide what will
happen tomorrow, I look back.
Oliver Wendell Holmes, Jr.
1.1 Introduction
The complete wireless professional does not
need to be a historian. One will be able to
design mobile radio networks or products
equally well whether aware or not that the
first demonstration of a radio transmission
was made by Hertz. However, the complete
wireless professional would do well to learn
from some of the lessons of mobile radio over
its history. Because of the dramatic change in
the design and deployment of mobile radio
over the last 100 years and the change in eco-
nomics and uses of radio systems, the most
relevant lessons are those from most recent
times. Hence, this chapter provides a short
summary of the historical background and
3
Contents
1.1 Introduction
1.2 Early history
1.3 Some key
milestones in mobile
radio history
1.4 Recent history
1
CHAPTER
tries to select some of the key lessons that can be learned. An excellent
description of the history of mobile radio development, including a
detailed analysis of the last 15 years of cellular deployment, can be found
in [1],1while a very readable biography of the founder of Motorola, Paul
Galvin [2], describes how Motorola shaped much of the development of
mobile radio from 1930 onward. This section provides a short summary of
the topics that the references describe in much greater detail.
The key issues that the complete wireless professional should learn
from this chapter are:
◗History, particularly recent history, has a number of important les-
sons that do not seem to have been learned by many in the mobile
radio business;
◗Standardization is far from an assured route to success, with the
global system for mobile communications (GSM) being the only stan-
dardized product among a wide range of standards to have been
highly successful;
◗Standardization of GSM took 13 years in total;
◗New radio systems such as cdmaOne can emerge from unexpected
sources and, with the right political and economic backing, can
become important globally.
1.2 Early history
Some of the key historical developments leading to today’s mobile radio
systems are shown in Figure 1.1.
The first radio transmissions are attributed to Heinrich Hertz in 1885.
The first radio system was very simple, using a switch and an induction
coil to generate a spark across two electrodes. The receiver was a loop
made from copper wire around 35 cm in diameter, with a small gap in the
loop. When the “transmitter” generated a spark, a small spark was seen to
jump the gap in the receiving coil. Spark transmission was used as the
basis for most radio equipment until around 1915 and is the reason why
radio operators are sometimes known as “sparks.” Hertz’s work aroused
4 The Complete Wireless Communications Professional
1. This is a superbly written and highly authoritative book and comes highly recommended.
much scientific interest, but it took the emergence of a scientist with busi-
ness acumen to move these discoveries into the commercial domain.
Some interesting history 5
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
Technical milestones Applications
Theoretical prediction of radio waves
Generation of radio waves (Hertz)
Tuned circuit (Lodge)
Aerial/earth system (Marconi)
Speech transmission (Fessenden)
Thermionic valve (Fleming)
Valve transmitter (Meissen)
First international spectrum
conference
Frequency modulation (Armstrong)
Cellular concept (Bell Labs)
Junction transistor (Schockley)
Digital integrated circuits
Solid state switches
Microprocessor
Cross-channel tests (UK)
Royal Navy (UK)
Transmission to automobile (US)
Merchant shipping (UK)
Transatlantic telegraph service
Radio direction finding (UK)
Aircraft use for artillery spotting (UK)
Transportables (UK)
Police use (Detroit, US)
Fishing boats (Norway, UK)
Aviation navigation and control
Telephones on ocean liners (UK)
Private mobile radio systems (US)
Operator controller mobile phones (US)
Automatic mobile telephones
Cellular test (US)
Cellular services (Japan)
Digital cellular networks (Europe)
Iridium satellite services launched
Figure 1.1 Key historical milestones.
Perhaps the father of today’s mobile radio systems was Guglielmo
Marconi, born in Italy in 1874. Marconi was first a scientist who made
the important breakthrough of redesigning the transmitter from a gap
between two electrodes to connecting one electrode to the earth and the
other to a metal pole placed on top of a mast (the aerial of today). By this
method, he was able to demonstrate transmissions over a range of a
few kilometers rather than just across the laboratory. Marconi tried to
approach the Italian Post Office for sponsorship of his work but was
unsuccessful. He then moved to the United Kingdom, where the British
Post Office was prepared to provide sponsorship. This proved to be a
shrewd move because the first application of mobile radio was in shipping
and, at the time, the United Kingdom had the world’s largest shipping
fleet. Marconi’s first sales of radio systems were in 1900 when the Royal
Navy ordered 32 sets at the equivalent of today’s cost of $500,000 per set
with annual royalty payments of $270,000 per set. It was revenue from
deals such as this that enabled Marconi to found a company and develop
new radio products. For some time, the Marconi company was the
world’s largest producer of radio equipment. Marconi was awarded the
Nobel Prize for Physics in 1907 and died in 1937. The company he
founded is now part of the General Electric Corporation (GEC).
Other important developments included the invention of the thermi-
onic diode in 1904, which lead to practical high-vacuum triodes by 1912,
facilitating the use of narrower band transmissions and making the trans-
mission of speech a possibility. The superheterodyne receiver was devel-
oped by Armstrong and Fessenden in 1912, and by 1933 Armstrong had
developed the concept of frequency modulation.
The First World War proved an important vehicle for demonstrating
the value of mobile radio in military maneuvers, especially for use by
spotter planes providing reports for artillery. The need for smaller and
lighter transmitters for planes hastened the reduction in size of radios to
the extent that they could be carried in a backpack.
After the First World War, the main impetus for developments came
from broadcasting. The rapid increase in the number of radio stations,
especially in the United States, resulted in a commercialization of receiv-
ers. It also resulted in efforts to coordinate the use of radio spectrum, and
the first international spectrum management conference took place in
Washington in 1927. This standardized the use of frequencies up to
1.5 MHz—the highest frequency thought to be of practical use for radio
6 The Complete Wireless Communications Professional
transmission. Some early experiments were also undertaken in what has
become known as private mobile radio. In 1921, the Detroit police experi-
mented with voice transmission to cars, but only in a one-way format,
and the Metropolitan police in London conducted a similar experiment
in 1923.
By the Second World War, domestic radio receivers were relatively
complex, with a high sensitivity and selectivity and the ability to receive
radio stations from around the world. During this period, two-way radios
slowly developed to the extent that some police forces were equipping
police cars with radio transmitters, but the high power consumption and
weight prohibited their universal acceptance.
The Second World War resulted in the mass production of mobile
radio equipment in order to equip the increasing number of military air-
craft and ships. Infantry backpack radios became more popular and
around 50,000 were manufactured in the United Kingdom during the
war. After the war, the manufacturers were looking for a market for their
large production capability and started to target the private mobile radio
(PMR)2market. Mobile phones were fitted in taxis from 1950 onward,
and the basic dispatch form of communications still used today, and
described in more detail in Chapter 4, was developed.
The next step forward was the development of the transistor, dra-
matically reducing the size and power consumption of radio systems and
enabling mass production of circuit boards to reduce prices. By 1965, the
first pocket-sized mobile phones were produced, allowing market growth
so that, for example, every policeman could be equipped with a mobile
radio rather than every car. The penetration of PMR at this time started to
owe more to the licensing and regulatory policies of the government
rather than the equipment or market acceptance, and even today this has
resulted in a situation where the United States has more than four times
the percentage penetration of PMR than the United Kingdom. Regulatory
policies and the implications for the mobile radio engineer are discussed
in more detail in Chapter 12.
Some interesting history 7
2. Private mobile radio is known as specialized mobile radio (SMR) in the United States and as
private business radio (PBR) in the United Kingdom, although PMR is by far the most
widely used abbreviation and will be adopted throughout this book.
1.3 Some key milestones in
mobile radio history
In describing the first cellular systems it is important to remember that
there is always a thin dividing line between PMR and what is today
known as mobile radio, typically cellular radio systems. Both are basically
transmitter/receiver units; the differences typically lie in the services with
which they are equipped. This is a topic to which we will return in more
detail in Section 14.2. The PMR systems described previously were typi-
cally technically able to provide some form of mobile radio service but
were normally prohibited from interconnection to the telephone system
(and still are today) both to prevent longer calls (which are typical of con-
necting to a landline subscriber), which would therefore congest the radio
spectrum, and to preserve the licensed (at the time monopoly) provision
of cellular radio services. The first mobile phone service was introduced
by AT&T in 25 U.S. cities in 1946 and called Mobile Telephone Service (MTS).
It was not a cellular system because only single cells were used and opera-
tor intervention was required to set up calls. This was followed by the
Improved Mobile Telephone Service (IMTS), which also only used single cells
but allowed automatic call set-up using tone signaling. However, a short-
age of spectrum and a lack of government interest in correcting this situa-
tion prevented this system from providing any significant capacity and it
made little impact.
In Sweden, the first European mobile radio system was introduced in
1955 by Televerket; with modifications, this system existed until around
1981, when its subscriber base had grown to 20,000 users. In the United
Kingdom, the first commercial system, called System 1, was introduced in
1965 in London. It was expensive, had limited capacity and many draw-
backs, but was still heavily oversubscribed. The next variant, System 2,
was never deployed, but System 3 reduced the voice channel bandwidth
from 100 kHz to 25 kHz, increasing the capacity. This still fell a long way
short of the demand. It was not until the early 1980s that cellular mobile
phone systems were deployed, finally providing the dramatic increase in
capacity required to make mobile radio a mass-market product. The cellu-
lar concept is described in more detail in Chapter 2.
Much of the work on cellular systems was pioneered in the United
States. The cellular concept was first developed by Bell Labs in 1948, and
its parent company, AT&T, lobbied the government for radio spectrum for
8 The Complete Wireless Communications Professional
some time. In 1977, this eventually resulted in an assignment in the
800-MHz band, which is still one of the key frequency bands for mobile
radio. Trials based on this license took place until 1981 and provided very
encouraging results. The trials convinced the U.S. regulator, the Federal
Communications Commission (FCC), that cellular was a viable concept.
There then followed a long period during which the FCC tried to deter-
mine how to best assign licenses for cellular, the start of a protracted and
still ongoing process of selecting the optimum way to assign licenses that
is described in more detail in Section 12.3. In this case, awarding the
licenses based on the quality of the application (the “beauty contest”
process) failed to work due to the huge number of applicants, making
evaluation highly difficult. The FCC overcame this using the lottery
approach of selecting licenses at random; it proved to be a highly unsatis-
factory approach that resulted in the substantial trading of licenses after
the award. In fact, the United States took over seven years to award all its
licenses; all the delays resulted in a high cost to the U.S. economy in fore-
gone revenue and growth. U.S. cellular deployments were based on the
Advanced Mobile Phone Service (AMPS)—a standard still in widespread use
today. However, the AMPS standard only defined the air interface; most
operators used different approaches to switching and billing, with the
result that roaming between different regions in the United States, of
which there were more than 90, was not possible. For a more detailed
description of cellular in general and AMPS in particular, see [3].
Developments were also taking place in other parts of the world.
In the Nordic countries, the Nordic Mobile Telephone at 450 MHz
(NMT450) was being developed with the advantage that it would allow
roaming to other Scandinavian countries. NMT900 was subsequently
introduced because the capacity of the 450-MHz frequencies proved
insufficient. Other European countries adopted a range of systems, some
developed within the country and only used for that country. Others
adopted a modified version of AMPS known as a Total Access Communica-
tions System (TACS) that operated in the 900-MHz band. In Europe, this
stage of mobile radio development, lasting from around 1985 to 1991,
was generally marked by monopoly provision. Most countries only pro-
vided a license to the existing state Post and Telecommunication Organization
(PTO). Only the United Kingdom took the unusual steps of introducing
competition by issuing two licenses and preventing the PTO from owning
either of these licenses (although they were allowed to take a minority
Some interesting history 9
shareholding). Competition is now recognized as important in the provi-
sion of mobile radio services, and the European Commission (EC) mandates
that members must have a competitive mobile radio environment.
1.4 Recent history
The recent history of mobile radio since 1991 has been dominated by the
introduction of digital mobile radio and the attempts to standardize third
generation systems. Key within this history are the roles of the GSM,
CDMA technologies, and the third generation concept and the success (or
otherwise) of standardization. It is this history that is probably of greatest
interest to the complete wireless professional because the lessons of this
period are likely to be highly relevant over the coming years.
GSM Mobile radio since 1991 has been dominated by the GSM system.
However, in 1991, it was far from clear that this would be the case. Stan-
dardization of GSM started in 1982 within the Conference Europeenne des
Administrations des Postes et Telecommunications (CEPT)—the European
spectrum management body. Although CEPT had standardized many
products in the past, they were far from successful. Typically, CEPT stan-
dardization was led by engineers with little regard for commercial reality
and with a desire to see their own ideas incorporated into the standard.
The standards that were developed, such as X25, were often ambiguous
and resulted in various national implementations, preventing interwork-
ing in the form envisaged. The track record of other standards bodies was
also not good. In most cases, the development of standards took so long
that national solutions had already been developed and the acceptance of
the standard was low. Hence, there was little reason to suppose that GSM
standardization would be successful (and indeed, little reason to suppose
that other standards, such as the digital enhanced cordless telephone (DECT)
or the terrestrial trunked radio (TETRA), would be successful simply
because GSM was). Standardization will be discussed in more detail in
Chapter 13, but an important lesson of history is that standardization of
complete mobile radio systems is more likely to fail than to succeed.
The reasons for the success of GSM are varied. One key point was
that standardization began early—before almost any manufacturer had
started to develop their own digital mobile radio standard. This prevented
different manufacturers from going different ways and ensured that there
10 The Complete Wireless Communications Professional
was sufficient time for the relatively slow standardization process to pro-
duce results before the product was required. The transfer of the stan-
dardization from CEPT to the European Telecommunication Standards
Institute (ETSI) helped to produce new “rules” about the manner in which
the standardization would proceed, making the standardization more
practical. Another factor was that the European Commission was in the
process of mandating GSM for use by cellular operators and that many
European countries were coming to a dead-end with the analog system,
which was expensive due to its proprietary nature and unable to provide
the additional capacity required. The inclusion of manufacturers into the
standards bodies was also a very important development compared to
previous CEPT standardization that included only the PTOs. The fact that
there was no major competing standard, particularly from the United
States, was also helpful. Finally, the vision of the participants, who fore-
saw the increase in semiconductor complexity, and the reduction in costs
helped provide a standard that was state of the art at its time of
completion. A more detailed assessment of the development of GSM is
provided by [1].
The progress of GSM has been far from smooth, with many delays en
route. The standardization proved much more complex than originally
anticipated and took a total of 13 years from the inception in 1982 to the
final delivery of the Phase Two specifications with all intended features in
1995. Other complex standards such as DECT and TETRA have taken
equally long periods of time. Considering that the next generation of
mobile radio standards will be even more complex, the long time taken to
develop the GSM standards should not be forgotten when remembering
the timescales suggested by those involved in third generation systems.
GSM is now installed in well over 100 countries. New operators mak-
ing a decision about the technology they should adopt often select GSM
because of the competitive supply of equipment, the large base of exper-
tise in deploying the network, and the fact that users can roam to other
countries. But clearly this was not the case for the first operators, who
experienced something of a chicken-and-egg problem; that is, once suc-
cessful, the standard becomes even more successful, but how does it
become successful in the first instance? In the case of GSM, operators in
Europe were mandated to use the technology, so hence a large volume
of sales was guaranteed, spurring the manufacturers to produce com-
petitive offerings. Many have complained about this mandating. For
Some interesting history 11
non-European manufacturers it provided a closed market, and for opera-
tors in Europe it removed choice. The issues surrounding technology
mandates are discussed in Appendix B.
It could be argued that this combination of a standard started early, a
guaranteed market base, a lack of competition from other standards, and
full European cooperation, not to mention the careful and skilled work of
those performing the standardization, is unusual and that standards are
more likely to fail than succeed. Indeed, there is much evidence that this
is the case. Unfortunately, many engineers only look back into history as
far as GSM and conclude that all European standards will be successful.
This is probably a rather selective use of history, as the following examples
demonstrate.
DSRR After the success of GSM, the EC started standardizing digital
versions of almost every possible radio system including PMR, short
range, cordless, and paging. Short range systems currently have a small
but steady market around the world. These systems do not use a base sta-
tion but communicate directly between mobiles in a “walkie-talkie”
mode (see, e.g., [4]). They are widely used in places such as building sites
and department stores where a number of people work in a relatively
small area. The EC decided that Europe needed a digital standard for these
applications and started the digital short-range radio (DSRR) standardiza-
tion project. The scope of DSRR rapidly grew from a simple “back-to-
back” radio system to one where terminals could relay messages to other
terminals and had security features and complex digital encoding. With
GSM, the approach of making the phone highly complex had worked
because the economies of scale allowed this complexity to be added at lit-
tle cost. The DSRR standards body failed to realize that DSRR would have
much lesser economies of scale; in any case, these advanced facilities were
not required by the user, who valued low cost above all. The DSRR stan-
dard was completed in 1993, but no product has ever been produced to
this standard. Instead, Motorola has introduced a short-range business radio
(SRBR) based on very simple analog transmission and with the user
manually selecting one of three channels. SRBR has proved very success-
ful in meeting the market requirements for simplicity and low price.
Standards bodies are not very good at producing simple standards.
With multiple parties attending the standardization, the requirements
from each tends to get added to the total specification. It is difficult to
restrict the capabilities with arguments about economic viability because
12 The Complete Wireless Communications Professional
these are hard to quantify. Complex standards can be advantageous when
there is a large market but often cause the failure of a standard.
TETRA and APCO25 The European standard for PMR, TETRA may
be moving down the same route. TETRA is discussed in more detail in
Section 4.3, and its role in future mobile communications is discussed
in Section 14.2. Yet again, the TETRA specification has proved to be
highly complex, with TETRA providing many more facilities than
required by most of the users. Manufacturers are countering this to some
extent by building equipment that does not have all the features in the
specification, but whether this will be sufficient to generate a large
enough market to cover the development costs is far from clear.
The United States has a project similar to the European TETRA project
known as APCO25 that is being standardized within the Telecommunica-
tions Industry Association (TIA) TR8 committee (standardization commit-
tees are explained in more detail in Section 13.2). APCO has very similar
goals to TETRA and, like TETRA, is targeted primarily at emergency serv-
ices users. The key difference between TETRA and APCO is that TETRA
uses time division multiple access (TDMA) while APCO25 uses frequency
division multiple access (FDMA)—access methods are explained in
Section 2.4.8.
Telepoint Another interesting lesson is that of telepoint. The cordless
and telepoint application is discussed in more detail in Section 5.2 and,
again, Garrard [1] provides an excellent analysis of their history. Tele-
point shows that modifying a standard from its original purpose is danger-
ous and that the success of mobile radio is not simply borne out of a desire
for anything that can communicate without wires but for a product pro-
viding particular features. After the success of cellular in the United
Kingdom, the government was keen to introduce more competition, and
other industry players were keen to enter the market. The cordless stan-
dard, CT-2, developed for indoor extensions to fixed lines, seemed to offer
a way to meet these requirements. By deploying a large number of cord-
less base stations in cities, the telepoint operators thought that they could
provide a service similar to cellular with the added advantage to the users
that they could use the same phone in their home, communicating with
their home base station. Telepoint licenses were fiercely contested in the
United Kingdom and about 10,000 base stations were deployed around
the country. Users, however, were not impressed by a service that could
Some interesting history 13
only be used in cities, that could not accept incoming calls, and where the
handsets were just as expensive as cellular.
It seemed obvious to many at the time that telepoint coverage is too
expensive to provide and that coverage is a critical issue to users. The tele-
point operators appear to have been blinded by a desire to operate a
cellular-type network and the equipment manufacturers by a desire to
sell more products. Even more bizarre was the entry into the U.K. market
of another operator (Hutchison Rabbit) after the first four operators had
failed. Estimates are that Rabbit never managed to have as many subscrib-
ers as it did base stations. History has shown that mobile radio can be highly
successful, but only if it provides the service that the subscriber wants.
CDMA and TDMA One of the key debates of recent years has been
whether code division multiple access (CDMA) or TDMA is the more appro-
priate access scheme for mobile radio. This debate is explored in more
detail in Section 14.4. In fact, and little realized by many engineers, the
debate has been less about the ideal access scheme and more about
whether operators should select GSM or a standard developed by the U.S.
company Qualcomm, now called cdmaOne (previously referred to as
IS-95). The debate, although overtly technical, has really been an issue of
trying to market cdmaOne as better than GSM. When cdmaOne was
announced in the early 1990s, it seemed unlikely that it would succeed.
The company that designed it was relatively small and little known in the
world of mobile radio. Standards were already established in Europe
(GSM), and the U.S. standard (digital AMPS, or D-AMPS) was supported
by the key manufacturers. However, today, cdmaOne is probably the
world’s second standard, after GSM. Understanding how this occurred is
an interesting historical lesson.
Probably, Qualcomm could only have succeeded with cdmaOne in
the United States. This is one of the few countries that:
◗Allows any manufacturer to develop a product that they can then
offer as a standard (unlike Europe where there can only be one
jointly developed standard);
◗Has a large enough home market to produce good economies of
scale in the case that the standard is not accepted elsewhere;
◗Is sufficiently advanced in the development of cellular technologies
that much of the rest of the world looks toward them for leadership.
14 The Complete Wireless Communications Professional
Clearly, Qualcomm would not have (and has not) succeeded in
Europe where the European standard was mandated. Key in the success
of Qualcomm was their linkage with a number of other manufacturers
and the desire of the United States to have a homegrown product rather
than importing the European product and hence losing leadership in
cellular. Other countries such as South Korea also rebelled against
European dominance and insisted that their operators deploy cdmaOne,
with equipment purchased from South Korean producers in order
to encourage local industry. Qualcomm’s astute use of partnerships
and exploitation of the backlash against European dominance enabled
cdmaOne to become a key global standard. Politics and national sensitivi-
ties are likely to play a key role in the future development of mobile radio
standards.
Third generation Third generation systems are intended to be the
replacement technology for existing second generation digital systems
such as GSM. The concept of third generation is described in more detail
in Chapter 11. Here, it is interesting to examine its progress to date. When
third generation was first announced, the key attribute was the ability to
provide service to all users, including cellular, cordless, PMR, and satel-
lite, all within the same system. One of the uses was data rates up to
2 Mbps in some environments, although at the start of the standardiza-
tion this was not a key requirement. During the time that the standards
bodies were making little progress trying to agree on the basic structure of
third generation, GSM was quietly evolving to provide service to nearly
all users including PMR, satellite, cordless, and others. Suddenly, the
third generation standards committees realized that their requirements
had mostly already been met—with the exception of the 2-Mbps data.
This now became the key requirement for third generation without any
real indication that it was required by the users or that it was practical to
provide given the limitations of radio spectrum.
Third generation standardization is ongoing and it will be interesting
to watch the development of the standard. However, those doing the
standardization seem to have trouble recognizing that the direction of the
standardization might need to change. Nor do they appear to have
learned the lesson from GSM that such standardization might take
13 years or more. Much of the standardization is performed by engineers
who would do well to look at recent historical experience.
Some interesting history 15
References
[1] Garrard, G., Cellular Communications: World-Wide Market Developments,
Norwood, MA: Artech House, 1997.
[2] Petrakis, H. M., The Founder’s Touch—The Life of Paul Galvin of Motorola,
Chicago: Motorola University Press, 1991.
[3] Bell System Technical J., Vol. 58, No 1, Jan. 1979.
[4] Walker, J., ed., Advances in Mobile Information Systems, Norwood, MA:
Artech House, 1998.
16 The Complete Wireless Communications Professional
Mobile radio
systems
In this section the key fundamentals of
mobile radio systems are introduced. The
intention is not to write a comprehensive
textbook covering all areas of mobile radio
technology—many excellent books exist
already—but to provide an overview. Armed
with the knowledge in this part, the complete
wireless professional should be able to under-
stand the key issues and know where to look
to find more detailed information if it is
required.
This section assumes a basic knowledge
of electrical engineering principles and some
simple mathematical capability. For those
who require a more basic introduction to
the principles of mobile radio engineering,
Understanding Cellular Radio by W. Webb
(Norwood, MA: Artech House, 1998) is a suit-
able introductory text.
II
PART
The basics of mobile
radio
Man’s business here is to know for the sake of
living, not to live for the sake of knowing.
Frederic Harrison
2.1 Introduction
The basic principles of mobile radio are best
understood by first studying the propagation
mechanisms by which the signal passes from
the transmitter to the receiver. From propa-
gation, this section examines the shortage
of radio spectrum and the complex system
designs required to provide sufficient system
capacity. Then the design of a typical system is
examined, providing a good understanding of
the basics of mobile radio communications.
The complete wireless professional needs to
have an understanding of:
19
Contents
2.1 Introduction
2.2 Basic principles
of propagation
2.3 Radio spectrum
utilization
2.4 Basic system
design
2.5 Packet and circuit
transmission
2.6 Theoretical
capacity of mobile
radio systems
2
CHAPTER
◗The likely received signal strength and the effect of slow and fast
fading and intersymbol interference (ISI) on the received signal (these
terms are explained later in this chapter);
◗The lack of radio spectrum and its implications for mobile radio sys-
tem design, including the means whereby spectrum can be reused;
◗The overall block-diagram design of a mobile radio system and the
need for each of the blocks;
◗The capacity (i.e., the number of subscribers) that can actually be
achieved from mobile radio systems.
This section provides a basic guide to these issues.
2.2 Basic principles of
propagation
An understanding of radio propagation is essential to the complete wire-
less professional because the loss in signal caused by propagation limits
the received signal strength, impacting on the quality of the received sig-
nal. Many of the building blocks of mobile radio systems, as introduced in
Section 2.4, are used solely to overcome the problems introduced by
propagation. These building blocks include error coding, equalization,
and to some extent the choice of multiple access scheme. There are many
detailed treatises on propagation, and the topic is covered in a wide range
of books such as [1–3], in most cases in a highly mathematical fashion.
Here the key issues are introduced.
If the received signal strength at a mobile radio is plotted against time,
then the trace would show a great deal of complexity that would typically
take substantial effort to understand. To simplify the analysis of radio
propagation, engineers generally consider the received signal strength to
be a composite of three discrete effects known as path loss, slow fading,
and fast fading. Although such characterization does not exactly reflect
reality, it has proved to be sufficiently useful and accurate to model
mobile radio systems and is in widespread use to date. Each of these sepa-
rate elements is now examined.
20 The Complete Wireless Communications Professional
Path loss Path loss is the simplest of all the propagation mechanisms to
understand and reflects the fact that the signal drops as the distance from
the transmitter increases. Theory shows that if the transmitter were in
“free space” (i.e., some distance away from any object), then the signal
would radiate in an expanding sphere from the point source of the trans-
mitter. Since the surface area of the sphere is proportional to the radius
squared, the received signal power at a distance dfrom the transmitter is
proportional to 1/d2. Free-space loss cannot occur on the Earth since one
half of the expanding sphere is under the ground which has a certain
reflection and transmission coefficient depending on the material making
up the surface of the Earth at that particular point. Of more relevance is
the fact that there will be obstructions on the ground in the form of build-
ings, hills, and vegetation, for example. These absorb and reflect the sig-
nal, resulting in a received signal strength that is much lower than that
predicted using free-space loss. Because of the complexity of modeling
every building, general guidelines are adopted as to the loss likely to be
experienced. Measurements have shown that in an urban environment,
if the path loss is modeled as being proportional to 1/d3.5, or in some cases
1/d4, then the results achieved best reflect real life. Empirical models,
such as that from Hata, introduced in Chapter 7, take the analysis one
stage further by modifying the exponent according to the height of the
mobile antenna, with the exponent falling by around 0.6 for each order of
magnitude increase in the height of the mobile antenna. This reflects the
fact that as the mobile antenna rises, buildings and other obstructions
have increasingly less effect and, hence, the path loss can come closer to
free space.
There are a few isolated cases where path loss exponents lower than
the exponent of 2 predicted by free space are experienced. These typically
occur in constrained spaces, often in corridors in a building. Here, the sig-
nal does not expand on the surface of a sphere because the walls of the
corridor cause the signal traveling toward them to be reflected back into
the corridor. Because the signal is now moving forward on a surface that
is not expanding (assuming the corridor stays the same width and
height), theory would predict that no loss in signal strength will occur. In
practice, some signal leaks through the corridor walls and exponents of
around 1.6 to 1.8 can be realized.
Slow fading The word fading is used to describe a drop in the received
signal strength, over and above that which would be expected based upon
path loss. This loss occurs temporarily. There are two phenomena in
The basics of mobile radio 21
mobile radio that cause fading to occur, one that causes fades lasting of
the order of a few seconds and one causing fades lasting of the order of a
few microseconds. The former is termed slow fading, while the latter is
termed fast fading. To see a slow-fading waveform it would be necessary
to take a set of measurements made by a mobile; to remove the effects of
path loss by correcting for the distance from the transmitter at any point,
using a formula such as that determined by Hata; and then to filter the
remaining signal such that any high-frequency changes, lasting less than
a second, were removed. The resulting waveform would typically show a
signal falling by around 8 dB or so over a period of a few seconds and then
rising back up to the mean level.
This fading phenomenon is caused by the receiver temporarily pass-
ing behind obstacles that partially block the signal from the transmitter. A
clear example of this is realized when driving down a street that has
detached houses between the base station and the mobile. When behind
the houses the signal strength will be reduced, whereas when between
them the signal strength will rise back to the expected level. The depth of
the fade will depend on both the amount of loss of the signal in passing
through the building and the strength of signals received by other mecha-
nisms such as reflection. The duration of the fade will depend on the time
it takes the mobile to traverse the building.
Measurements have shown that if a plot of the slow-fading waveform
is periodically sampled and the probability of any particular level of signal
strength plotted, then the results will follow a log-normal distribution
(i.e., a normal distribution plotted on a logarithmic scale) with a standard
deviation of around 8 dB.
Fast fading Fast fading can easily be seen on the plot of received signal
strength if only a small portion of the plot, of duration say 1 sec, is exam-
ined. Alternatively, it can be shown by filtering out all low-frequency
changes in the received signal. The cause of fast fading is multipath propa-
gation. In a complex urban environment, the mobile will receive many
copies of the transmitted signal each traveling via a different path. Some
will come direct to the mobile, others will reflect off buildings, cars, or
other objects. The simplest arrangement of a mobile receiving a direct and
a reflected signal from the transmitter is shown in Figure 2.1. In real life,
the receipt of a direct signal is relatively rare, and the mobile is likely to
receive numerous reflections from all around. Each of these signals has
followed a different path from the transmitter to the receiver and so is
likely to have a different signal strength. The length of each path will also
22 The Complete Wireless Communications Professional
be different, with the result that each wave will take a slightly different
time to arrive at the mobile. This will result in the phase of the carrier
wave being different for each of the received waveforms.
Imagine the simple case where there are two received waves, both of
the same signal strength, and that one results from a reflection of a mov-
ing object, so that over time the distance this second wave travels
increases. The result is shown in Figure 2.2, where the top trace shows the
first wave, the second trace the reflected wave, and the third trace the
composite signal as seen by the receiver. It is clear that at the point at
which the waves are in exact antiphase there is complete cancellation
of the received signal, resulting in a fade that extends to zero received
signal strength. At a transmission frequency of 900 MHz, the transition
from constructive interference to destructive interference as shown in
Figure 2.2 would take half a wavelength, approximately 15 cm. Hence,
each time the mobile moves a full wavelength, around 30 cm, it is likely to
pass through a fade. A mobile will travel this distance in a very short
period of time—hence, the term fast fading.
This can alternatively be represented by a process of vector addition as
shown in Figure 2.3, where the magnitude of the vector represents the
strength of the signal, and the angle of the vector from the origin (in an
anticlockwise direction) represents the phase difference between the
“reference” signal (the strongest path) and the particular received signal.
There can be a number of vectors each corresponding to a different
received path. In the case that the received signals are exactly in phase (as
is the case at the start of Figure 2.2), the vector diagram consists of two
vectors superimposed on top of each other. In the case that the vectors are
in exact antiphase (as is the case at the end of Figure 2.2), the two vectors
are of equal magnitude but opposite polarity. Clearly, addition of the two
vectors in the first case would result in a single vector along the origin of
The basics of mobile radio 23
Line-of-sight path
Reflected path
Figure 2.1 Multipath propagation.
twice the magnitude, whereas in the second case the result of the addition
would be no remaining signal. Figure 2.3 shows the vector diagrams and
resulting addition for the cases of phase differences of 90 degrees and
180 degrees.
It real life, the prospect of exact cancellation is very remote since no
two waves will typically have the same signal strength. However, the
probability of a partial cancellation is very high, with the result that the
signal will fluctuate by as much as 40 dB from the mean level while the
mobile passes through fades. Figure 2.4 shows what a typical fast fading
signal would look like. Fast fading is also known as Rayleigh fading, after
the physicist who developed the statistics that can be used to describe it.
24 The Complete Wireless Communications Professional
−2
−1
0
1
2
−2
−1
0
1
2
−4
−2
0
2
4
Figure 2.2 The top trace represents the wanted signal, the second
the interfering signal, and the third the received waveform.
Mathematically, Rayleigh fading is modeled by the combination of
in-phase and quadrature signals, both having a normal distribution with
variance σ2. Then the amplitude of the received signal is given by
() () ()
ak ak ak
iq
=+
22 (2.1)
where aiand aqare the in-phase and quadrature waveforms, respectively.
The mathematics of deriving the distribution of the amplitude are com-
plex and detailed in [4]. In the case that there is no dominant path to the
mobile, the probability of the signal having a particular amplitude ais
given by
The basics of mobile radio 25
Above: Vectors corresponding to
paths shifted by 90
Below: The resulting signal, shifted by
45 with a magnitude of 1.41
°
°
Above: Vectors corresponding to
paths shifted by 180
Below: The resulting complete
cancellation of the signal
°
Figure 2.3 Vectorial representation of multipath signal reception.
()
pa
ae
a
Rayleigh =−
σ
σ
2
2
2
2(2.2)
A graph of this equation for the case σ=1 is shown in Figure 2.5,
where it can be seen that the highest probability is for the signal to have
no fading; that there is a significant probability of fades as deep as 22 dB;
and that the tail of the graph asymptotically approaches the x-axis, result-
ing in a small probability of an infinitely deep fade.
If there is not a line-of-sight (LOS) path between the transmitter and
the receiver, and typically there is not, then there are only two mecha-
nisms by which the radio signal can propagate from the transmitter to the
receiver, namely, reflection and diffraction. At the frequencies used for a
26 The Complete Wireless Communications Professional
−40
−35
−30
−25
−20
−15
−10
−5
0
5
10
Time (0–1 sec)
Signal level (dB)
Figure 2.4 Rayleigh fading waveform for a mobile moving at
walking speed over 1 sec.
0
0.2
0.4
0.6
0.8
Signal strength (dB)
−30 −26 −22 −18 −14 −10 −6−22 610
Probability
Figure 2.5 Probability of a Rayleigh fading signal strength.
mobile radio system, diffraction results in very high levels of path loss;
hence, reflection is by far the most important phenomenon.
Reflection simply results from the signal reflecting from the surfaces
that it encounters rather than being absorbed by them. The amount
of reflection depends on the reflective, absorptive, and transmissive
characteristics of the surface the wave encounters. Sheet metal pro-
vides near-perfect reflection, while glass and paper provide near-perfect
transmission. Materials such as brick result in some reflection, some
absorption, and some transmission. Typically, the surfaces encountered
in real life are rough; hence, any reflections are diffuse, spreading the
signal over a larger area but resulting in a lower signal strength.
Diffraction allows signals to bend over the edge of obstacles. Modeling
diffraction is highly complex and typically is only tractable for the ideal-
ized “knife-edge” case where the obstacle encountered can be considered
to have minimal width [1, 2]. The key issue with diffraction is the angle
through which the signal can diffract. When a large angle of diffraction
can be achieved, it is possible for the signal to “re-form” after passing
around an obstruction. With lower angles, a “shadow” is formed behind
the obstruction. For the knife-edge, Figure 2.6 shows the variation of sig-
nal strength of a diffracted signal with parameter v, while Figure 2.7
shows how the signal strength for a given diffracted angle varies with
frequency.
The parameter vis given by
()
νλ
=+
⋅
hdd
dd
212
12 (2.3)
where d1is the distance from the transmitter to the obstruction, d2the dis-
tance from the obstruction to the receiver, hthe height of the obstruction,
and λthe wavelength of the transmitted frequency. For a possible GSM
network deployment in a city with d1=1,000m and d2=200m, at
1,800 MHz the parameter v=0.28h. Hence, using Figure 2.6, if h=0 (i.e.,
the LOS path grazes the top of a building) the diffraction loss will be
around 5 dB, while if the height is 10m (corresponding to a total angle of
diffraction of 3.43 degrees) the loss will be around 22 dB. A little further
analysis soon shows that diffraction angles of greater than 1 degree are
likely to result in insufficient signal strength at the frequencies of interest.
As Figure 2.7 shows, the loss is frequency dependent, but as the loss is
The basics of mobile radio 27
already severe, the frequency variation is unlikely to be the overrid-
ing issue.
28 The Complete Wireless Communications Professional
5
0
0
−5
−10
−15
−20
−25
Loss (dB)
V
−3
−2
−1
1
2
3
Figure 2.6 Variation of diffraction loss with parameter v.
Loss (dB)
Frequency (MHz)
−6
−8
−9
−10
−11
−12
−13
−7
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
5,500
6,000
Figure 2.7 Variation of diffraction loss for a particular obstruction
with frequency.
Wideband channels There is a further difficulty that may be caused
by fast fading. If the reflection comes from some faraway object, then the
delay of the reflected signal will be large. If this delay is greater than the
time taken to transmit a bit of information, then when the reflected signal
finally arrives it carries different information to the direct signal. The
result of this is that the previous bit transmitted, or symbol, interferes
with the current symbol, generating a phenomena known as ISI. ISI is
problematic in mobile radio systems that have transmission bandwidths
greater than around 100 kHz. In order to understand whether the prob-
lem might occur, consider the following example.
Assume that the symbol rate is 100 kHz (broadly this means that the
bandwidth of the transmitted signal will be around 100 kHz). The carrier
frequency is not a relevant factor in calculating ISI. (The symbol rate can
be assumed to be equal to the bit rate for the purposes of this discussion.)
If the reflection is delayed by 1/100 kHz, namely 10 µs, then the reflected
signal will arrive during the next symbol period causing ISI. In 10 µs, radio
signals travel 3 km. Hence, if the reflection occurs from an obstacle 1.5 km
past the receiver, ISI will occur.
As the symbol rate increases, the distance required for ISI to occur
reduces proportionally. With a bandwidth of 1 MHz, the distance falls to
300m; and at 10 MHz, down to only 30m. Some of the wireless local loop
(WLL) systems discussed in Section 5.3 have bandwidths in excess of
1 MHz, and hence ISI might be expected to be problematic.
To further explain ISI, consider Figures 2.8 to 2.10. In each case the
figures show three lines. The top line is the signal received directly by the
mobile, where in this case a 010101… data stream has been sent. The sec-
ond line is the signal received with some delay, although here it has been
assumed that it has been received with the same signal strength. The bot-
tom line is the composite from the first two signals, that is, the signal that
the mobile radio actually receives.
In Figure 2.8, the received signal in the case that the delay is only
one-fourth of a bit period is shown. The resultant signal is still clearly dis-
tinguishable as a 010101…transmission; however, the length of time
that the trace spends at the level corresponding to 1, or to 0, is reduced,
increasing the importance of accurate timing within the receiver. In this
case, the interference would be judged to be Rayleigh rather than ISI
because the delayed signal was delayed by less than a bit period. In
Figure 2.9, the delay has been increased to three-fourths of a bit period. At
this point, the interference is verging upon becoming ISI. Here, the
The basics of mobile radio 29
30 The Complete Wireless Communications Professional
Figure 2.8 Received signals in the case that the delay is only
one-fourth of a bit period.
Figure 2.9 Received signals in the case that the delay is only
three-fourths of a bit period.
010101…signal could be recovered, but only with a perfectly synchro-
nized receiver.
Finally, Figure 2.10 illustrates the case where the delay has become
exactly a bit period. In this case, it has clearly become impossible to distin-
guish the transmitted information unless some additional intelligence is
employed in the receiver. Now imagine the case that the transmitted data
signal were 0011001100…. In this situation, it would actually be possible
to distinguish the transmitted data until the delay was equal to two bit
periods. Hence, ISI has the effect of rendering some transmitted data
sequences unreadable, but not others. For this reason it is sometimes
called frequency selective fading because if the transmitted data contained a
range of frequencies and the frequency content of the received data was
examined (e.g., using a spectrum analyzer or conducting a Fourier trans-
form), then the received signal would appear to be missing certain fre-
quencies (such as the frequency of the 101010… pattern in our example).
ISI can be corrected through the use of equalizers, which are discussed in
more detail in Section 2.4.4.
The basics of mobile radio 31
Figure 2.10 Received signals in the case that the delay is a complete
bit period.
2.3 Radio spectrum utilization
Radio spectrum is the one fundamental requirement for cellular and
wireless communications. All radio communications require radio spec-
trum, the amount required being approximately proportional to the
bandwidth of the information to be transmitted. It was once said, “Spec-
trum is like real estate—they just don’t make it any more.” This is quite an
apt description. Spectrum is quite like land—there is only a limited supply
of it and some parts are more valuable than others. For example, certain
parts of the radio spectrum have characteristics that particularly suit cel-
lular radio, and these parts of the spectrum are in much demand from all
the companies who would like to be cellular radio operators.
Radio spectrum is usually managed by the government or their agen-
cies—for example, the FCC in the United States. It is their role to ensure
that the rights to use the spectrum are given out fairly to all those who
need it and to make sure that no two people are given the same bits of
spectrum. Giving out radio spectrum fairly is a difficult task. It is a little
like trying to fairly distribute the welfare budget; everyone seems to have
a valid claim and there is not enough to go around. Recently, some gov-
ernments have resorted to selling the rights to the spectrum on the basis
that the person who is prepared to pay the most must be the person who
needs the spectrum most badly. When enough cellular spectrum for
around six cellular operators was auctioned in the United States in 1997,
the government received $20B in revenue.1This shows just how scarce
the spectrum is and how much people are prepared to pay for access to it
and is a topic to which we will return to in more detail in Chapter 12.
What has tended to happen in most countries is that certain parts of
the radio spectrum, such as the 900- and 1,800-MHz bands, have been set
aside for cellular. This, and some other parts of the spectrum, have then
been divided typically between three or four different cellular operators,
with the net result that each operator has been given something like
25 MHz of radio spectrum each, normally partitioned into an uplink and a
downlink band, and so the assignment is written as 2 ×12.5 MHz. The
shortage of radio spectrum impacts upon most of the design issues of both
32 The Complete Wireless Communications Professional
1. Actually, to be more accurate, it received pledges for over $20B. Subsequently, some of
the largest bidders have defaulted on their payments with the result that the amount
actually received is much less. We return to this issue in Section 12.3.
the mobile radio technology and of the network and is a critical point to be
understood by the complete wireless professional.
To understand whether there is sufficient spectrum it is important to
understand how the capacity of a cellular system is calculated. We first
discuss the underlying theory. The capacity of a cell in terms of the
number of radio channels is given by
mB
BK
t
c
=
(2.4)
where Btis the total bandwidth (spectrum) assigned to the operator, Bcis
the bandwidth required per call, and Kis the cluster size or reuse factor.
Assuming that the operator has been given a fixed spectrum assignment
and that they have selected a technology with a fixed bandwidth per call
(as is typically the case), the remaining variable is the cluster size. The
concept of a cluster is best understood with the aid of Figure 2.11. First a
few words about this figure. You will note the cells are shown as hexa-
gons. This is something of a joke in the cellular industry where nobody
has yet seen a hexagonal cell in real life. Cells in real life are more or
less circular (because of the way radio waves propagate, as explained
The basics of mobile radio 33
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Figure 2.11 A cluster of cells.
previously), but unfortunately circular cells do not tessellate.2A hexagon
is quite close in shape to a circle and does tessellate, and so most cells are
drawn as hexagons to ease understanding.
In Figure 2.11 cells are named A to P. Now imagine that it was decided
to use frequency 1 in cell A. The same frequency certainly cannot be used
in cells B, F, or E because they adjoin cell A, and so there would always be
interference at the edge. Typically, it cannot be used in cells C, G, J, or I
either because the interference there will still be too great. However, it
could be used again in cells D, H, K, O, N, or M. If we assign our frequen-
cies on this basis, the result might start to look like Figure 2.12. Because
only seven frequencies are required, it is said that there is a cluster size of
seven.
Like the cluster size, the other important concept is to understand the
number of radio channels required in a particular cell. Typically, the mar-
keting department will determine how many subscribers they expect and
the number of call minutes per busy hour that they expect the subscribers
to make. Based on this information, the engineers need to determine how
many radio channels will be needed to meet this demand. This concept is
discussed in more detail in Chapter 7.
Traffic levels are turned into radio channels via the Erlang formula.
Erlang was a Swedish engineer working for the Swedish Post and Tele-
communications organization who worked on traffic levels in fixed net-
works, but his work is equally applicable to mobile networks. Erlang
developed two formulae relevant to mobile radio systems. The Erlang B
formula is given by
P
AN
An
N
n
n
N
B=
=
∑
!
!
0(2.5)
where PBis the probability of blocking, Ais the offered traffic in Erlangs,
and Nis the number of traffic channels available. One Erlang is one con-
tinuously used traffic channel, so during any given period (say one hour)
if a user talks for half the time they would be said to generation 0.5E. If
there are 10 users all talking for half the time, the total traffic load would
be 5E. The Erlang B formula applies to nonqueuing, or blocking, systems.
34 The Complete Wireless Communications Professional
2. Shapes are said to tessellate when they can be placed together on a flat surface without
either overlapping or leaving any gaps.
That is, when a user wants to make a call, if there are no channels avail-
able, then their request to make a call is blocked. This much is true of cel-
lular systems. However, the typical blocked user will immediately press
the send button again in the hope of getting a radio channel this time, and
this retry behavior is not allowed by Erlang B. Despite this, Erlang B pro-
vides results that are very close to real life for mobile radio systems and is
widely used. It is normal to apply the Erlang formula to the traffic levels
experienced during the busiest hour of the day, or “busy hour,” in order
to size the network for the worst case.
The number of traffic channels, N, required for a given Aand PBcan
only be solved iteratively by substituting values of Nin the preceding
equation until the desired PBis reached. As a result, tables of Erlang for-
mulae are available (a useful engineering tool is a spreadsheet macro per-
forming Erlang B calculations that can be quite simply written—an Excel
macro to perform this calculation is provided in Appendix A). A graph
showing the variation of radio channels required with Erlangs of traffic
The basics of mobile radio 35
5
4
6
1
3
7
2
5
4
6
1
3
7
2
5
4
6
1
3
7
2
5
4
6
1
3
7
2
5
4
6
1
3
7
2
6
7
5
5
6
7
Figure 2.12 The cluster repeated many times.
and different blocking probabilities is shown in Figure 2.13. Those wish-
ing to know more about the Erlang formula should consult [5].
There are a number of features to note about this figure. The first,
unsurprising fact is that as the required blocking probability gets lower,
more radio channels are needed to handle the same amount of traffic. For
a typical mobile radio system, blocking probabilities of around 2% are
considered acceptable, whereas for WLL systems blocking probabilities
below 1% are necessary.
The second is the slight steplike nature of these curves that is caused
by the fact that only an integer number (i.e., whole number) of channels
is possible.
The third is that the number of channels required tends toward
the number of Erlangs for high levels of traffic (e.g., using the 2%
blocking common in mobile radio systems, for 1 Erlang, 5 channels
are required—an efficiency of 20%; whereas for 19 Erlangs, 25 chan-
nels are required—an efficiency of 76%). This is known as “trunking
gain”—the more traffic that can be trunked together, the more efficient
the system.
Erlang also looked at the case where calls could be queued, as can
happen in some fixed networks. In this case, he derived the Erlang C
equation, given by
()
()
()
PpN p
pN
N
delay =−
0
1! (2.6)
36 The Complete Wireless Communications Professional
0
5
10
15
20
25
30
35
Traffic (E)
Pb 0.1%=
Pb 1%=
Pb 2%=
Lines required
1357911 13 15 17 19
Figure 2.13 Channels versus Erlangs for a range of blocking
probabilities.
where pis the utilization per trunk, given by the percentage of time the
trunk will be utilized during the busy hour; Nis the number of trunks; and
p0, the probability that there are no calls in the queue waiting to be served
is given by
() ()
Np
np
Np
N
n
n
NN
!!
=
−
−
∑+−
0
1
1
1
1(2.7)
Note here that instead of the probability of blocking, all calls are
queued until they are served, so there is a probability of delay. In such
queuing networks, the grade of service is normally specified in the form
“95% of all calls must experience a delay of less than 1 sec.” Erlang C does
not describe mobile radio systems well because typically call requests are
not queued. To date, there has not been a well-publicized formula that
exactly describes the mobile radio system taking into account repeated
pressing of the send button; hence, Erlang B remains the standard for-
mula in use.
2.4 Basic system design
2.4.1 System overview
In this section, the general design philosophies of radio systems are
explained. Each of the areas covered is highly complex and there will
typically be a number of specialized books and journal articles covering
the relevant issues. Here, an overview of the different areas is provided,
along with details of where further information can be discovered.
Figure 2.14 shows a block diagram of a stylized digital radio system. Note
that the ordering of blocks is important: speech coding must be performed
first, modulation and medium access last, and ciphering after error cor-
rection. Analog radio systems broadly do not have any of these steps and
are sufficiently simple that they do warrant further discussion here.
Each of the stages is now described in more detail.
2.4.2 Voice encoding
Any waveform, whether it is speech or from a different source, can be
converted from analog to digital by simply using an analog-to-digital
The basics of mobile radio 37
converter. All such converters sample the incoming analog signal at peri-
odic intervals and quantify the strength of the signal at that point. The
quality of signal representation in an analog-to-digital converter is meas-
ured by the number of samples per second and the number of bits used to
quantify the signal at that point—the higher each of these values, the
more accurately the signal will be represented. However, equally, the
higher both of these parameters, the greater the information generated
and the more bandwidth required to transmit the signal. Hence, a balance
needs to be struck between quality of representation of signal and band-
width required for transmission.
In all cases, there will be an error when the speech is recreated due to
a difference between the digital waveform and the original analog wave-
form. This difference is known as the “quantization error” and is shown in
Figure 2.15.
38 The Complete Wireless Communications Professional
Information source
Source encoder
(speech encoder)
Error coder
Interleaver
Modulator Radio channel
Information sink
Source decoder
(speech decoder)
Error decoder
Deinterleaver
Demodulator
Burst formatting
Ciphering
Reformatting
Deciphering
Figure 2.14 Block diagram of a radio system.
The difficulty resides in knowing what quantization error can be tol-
erated. The hearing process is complex and the ear is very sensitive to
some errors while very tolerant of others. Mathematical measures of
errors such as the root mean square (RMS) value of the quantization error
tend to be poor predictors of the speech quality as perceived by the user.
Instead, subjective listening tests are used, where a panel of users is asked
to rate the relative quality of a number of different speech coders, nor-
mally on a scale of 1 to 5. The average score is used to rate the speech
coder and is known as the mean opinion score (MOS). Hence, the process of
the design of speech coders becomes one of designing new coders and
then subjecting them to panel judgment.
In the case of the simple coder described previously, the sampling rate
should be set using the Nyquist theorem. This is a theorem that shows if a
waveform is sampled at twice its highest frequency sine wave compo-
nent, then using a knowledge of the amplitude and frequency of the vari-
ous components of the signal it would be possible to rebuild the original
signal. Speech contains frequencies up to around 15 kHz depending on
the speaker; however, most of these higher frequency components form
part of unvoiced consonants and can be “dropped” with only limited loss
of intelligibility. Indeed, the key components of a speech waveform reside
below 4 kHz. Hence, a sampling rate of 8 kHz is typically sufficient for
an acceptable voice quality (at least equivalent to existing telephone
systems).
The basics of mobile radio 39
Sample points Speech waveform
Recreated digital
waveform
Quantization
error
Figure 2.15 The speech sampling process.
Early speech coders used an agreed format. They took an analog-to-
digital converter set at a sampling rate of 8 kbps and sampled 8 bits each
time, resulting in a total data flow of 64 kbps. The quantization levels for
each sample were set in a slightly nonlinear fashion where they were
compressed at low signal levels and expanded for higher signal levels
because experimentation has shown that the ear is more subjective to
errors at low signal strength than at high signal strength. This speech-
coding technique is known as “µ-law PCM.” PCM speech coding is widely
used in fixed telephone networks where bandwidth is not so critically
constrained as for mobile networks and where high quality is considered
essential. Incidentally, this implies that there is generally little point in
producing a voice coder of higher quality than PCM since most calls will
pass through a fixed network at some point where their voice quality
will be reduced to PCM levels.
PCM is not an efficient way to encode speech. Speech waveforms
when considered over a short duration of time (e.g., 20 ms) are highly
repetitive and can be clearly seen to be composed of the superposition of a
number of sine waves. By taking account of the predictability and perio-
dicity in short samples of speech, near-identical quality can be achieved to
PCM coding but at much lower levels of transmitted information. The
most advanced speech coders try to model the manner in which the
speech is generated. The speech coders used by digital cellular systems fol-
low this route to a greater or lesser extent and are known as parametric
encoders because they encode the basic parameters of the speech wave-
form [1, 6].
In order to model human speech it is necessary to understand some-
thing about the manner in which it is generated. Human speech can be
considered as consisting of two different types of sound—voiced sounds
(vowels) with a regular, periodic structure and unvoiced sounds (conso-
nants) with a more noiselike characteristic that is less predictable. Exam-
ples of voiced and unvoiced waveforms are shown in Figures 2.16 and
2.17. The first task of a parametric encoder is to decide whether each
segment of speech is voiced or unvoiced. It then needs to determine:
◗The equivalent filter coefficients that characterize the vocal tract of
the speaker;
◗The loudness of the speech;
◗If voiced, the pitch information for the speech.
40 The Complete Wireless Communications Professional
The speech decoder then recreates the speech depending on whether
it was voiced or unvoiced in the following manner:
The basics of mobile radio 41
0510 15 20 25 30
Time (ms)
4,000
−4,000
3,000
−3,000
2,000
−2,000
1,000
−1,000
0
Amplitude
Figure 2.16 An example of voiced speech.
0510 15 20 25 30
Time (ms)
800
−800
600
−600
400
−400
200
−200
0
Amplitude
Figure 2.17 An example of unvoiced speech.
◗In the case of voiced speech, a periodic waveform is created with the
same pitch and loudness as the original and passed through a filter
with the appropriate coefficients.
◗In the case of unvoiced speech, random noise with appropriate
loudness is input into a filter with the appropriate coefficients.
In the basic form described, parametric coders are very efficient at
compressing speech to as little as 2.4 kbps. However, there are two prob-
lems that result in the speech quality being relatively poor:
◗Because speech is determined to be either voiced or unvoiced, in
the transition period between the different types of speech the qual-
ity will be poor.
◗Interactions between the sound source and the vocal tract are
ignored, resulting in a poor characterization of the speech in some
cases.
A solution to these problems is to use hybrid coders, also known as
analysis by synthesis (AbS) coders. Instead of simply assuming that the exci-
tation is either a periodic waveform or white noise, they transmit more
detailed information about the excitation either using a model of the
pulse shape, size, and spacing or by selecting one of a number of excita-
tion models from a code book. By selecting the best possible excitation
sequence, the aim is to minimize the difference between the encoded and
the decoded signals. A generic block diagram of an AbS speech coder is
shown in Figure 2.18.
AbS codecs divide the input speech into frames, typically about 20-ms
long. For each frame, parameters are determined for a synthesis filter,
which attempts to synthesize the vocal tract, and then the excitation to
this filter that most closely reproduces the speech signal is determined.
This is achieved by determining the excitation signal that when passed
into the determined synthesis filter minimizes the error between
the input speech and the reconstructed speech. Hence the name
analysis-by-synthesis—the encoder analyzes the input speech by synthesiz-
ing many different approximations to it. Once the analysis of the frame is
completed, the encoder transmits information representing the synthesis
filter parameters and the excitation to the decoder. At the decoder
the given excitation is passed through the synthesis filter set with the
42 The Complete Wireless Communications Professional
transmitted parameters to give the reconstructed speech. The synthesis
model may also include a long-term predictor (LTP) that models the pitch in
voiced speech, allowing the filter to shape the excitation signal more
accurately.
The error-weighting block shown in Figure 2.18 is used to shape the
spectrum of the difference between the input speech and the synthesized
speech signal in order to reduce the perceived effect of this error. This can
be achieved by noting that in frequency regions where the speech has
high energy any error will be partially masked by the speech, whereas in
the frequency regions where there is low energy any error will be highly
noticeable to the listener. The error-weighting filter emphasizes the noise
in the frequency regions where the speech content is low prior to the
error minimization function, concentrating any errors into frequency
regions where they will be least noticeable. Such weighting has been
found to produce a significant improvement in the subjective quality of
the reconstructed speech for AbS codecs.
The basics of mobile radio 43
Encoder
Decoder
Excitation
generation Synthesis
filter
Error
minimization
Error
weighting
Input speech
s(n)
^
s(n)
e(n)u(n)
e (n)
w
−
Excitation
generation Synthesis
filter
Reproduced
speech
s(n)
^
u(n)
Figure 2.18 Generic model of an AbS encoder.
There are many different types of AbS codecs depending on how the
excitation waveform for the synthesis filter is chosen. The perfect AbS
codec would pass every possible waveform through the filter to deter-
mine the excitation sequence producing the best possible match to the
input speech. However the numerical complexity involved in passing
every possible excitation signal through the synthesis filter is typically
intractable. For most codecs, some means of reducing this complex-
ity, without compromising the performance of the codec significantly,
is used.
There are broadly three different classes of AbS codecs known as mul-
tipulse excited (MPE), regular pulse excited (RPE), and code excited linear predic-
tion (CELP). The differences between MPE, RPE, and CELP codecs arise in
the manner in which the excitation signal is generated.
With MPE codecs, the excitation sequence is given by a fixed number
of pulses for every frame of speech. The positions of these pulses within
the frame and their amplitudes are determined by the encoder and trans-
mitted to the decoder. Determining the optimal position and amplitude
for each pulse is not computationally tractable; hence, a suboptimal
method of finding the pulse positions and amplitudes is used. Typically,
about 4 pulses per 5 ms are used, leading to good-quality reconstructed
speech at a bit rate of around 10 kbps.
The RPE codec also uses a number of pulses to characterize the excita-
tion signal. However, with RPE codecs the pulses are regularly spaced at
some fixed interval and the encoder needs only to determine the position
of the first pulse and the amplitude of all the pulses. Therefore, less infor-
mation needs to be transmitted about pulse positions; so for a given bit
rate, the RPE codec can use more pulses than MPE codecs. For example, at
a bit rate of about 10 kbps, around 10 pulses per 5 ms can be used in RPE
codecs, compared to 4 pulses for MPE codecs. This allows RPE codecs to
give slightly better quality reconstructed speech quality than MPE codecs.
However, they also tend to be more complex.
Although MPE and RPE codecs can provide good-quality speech at
rates of around 10 kbps and higher, they are not suitable for rates much
below this due to the large amount of information that must be transmit-
ted about the excitation pulses. In order to go below this bit rate it is
necessary to use a CELP coder. With CELP, a large number of poten-
tial excitation waveforms are prestored in both the encoder and the
decoder. The encoder tries each of the possible excitation sequences and
44 The Complete Wireless Communications Professional
determines which has the lowest error. It then sends the number describ-
ing the position of this codeword in the code book along with a power
level. Typically the code book index is represented with about 10 bits (to
give a code book size of 1,024 entries) and the gain is coded with about
5 bits. Thus, the bit rate necessary to transmit the excitation information
is greatly reduced—around 15 bits compared to the 47 bits used, for
example, in the GSM RPE codec. Considerable research is underway to
determine means to reduce the number of excitation sequences that need
to be tried for each sample of speech so as to simplify the design of CELP
coders. For example, it has been found that the CELP codec structure
can be improved and used at rates below 4.8 kbps by classifying speech
segments into one of a number of types (e.g., voiced, unvoiced, and tran-
sition frames). The different speech segment types are then coded differ-
ently with a specially designed encoder for each type.
The GSM full-rate speech codec is an example of a RPE codec operat-
ing at 13 kbps. The input speech is split up into 20-ms-long frames, and for
each frame a set of eight short-term predictor coefficients are found. Each
frame is then further split into four 5-ms subframes, and for each sub-
frame the encoder finds a delay and a gain for the LTP. Finally, the resid-
ual signal after both short- and long-term filtering is quantified for each
subframe. This residual signal is decimated into three possible excitation
sequences, each 13 samples long. The sequence with the highest energy is
chosen as the best representation of the excitation sequence, and each
pulse in the sequence has its amplitude quantified with three bits. At the
decoder the reconstructed excitation signal is fed through the long term
and then the short-term synthesis filters to give the reconstructed speech.
A postfilter is used to improve the perceptual quality of this reconstructed
speech.
An area of recent progress has been in variable-rate speech coders.
Such coders generate more information when the user is speaking and
less information when he or she is not. Advanced variable rate coders
typically have around eight different rates that are selected depending on
the amount of information required to characterize the speech. A 20-ms
section of speech is sampled, the amount of voice activity measured,
and an appropriate coder rate set for that section. The first of this type
of coder was developed by Qualcomm and called PureVoice™. More
recently the GSM standards committees are working on an advanced mul-
tirate coder (AMR coder). Such speech coders are extremely complex
The basics of mobile radio 45
and beyond the scope of this book; suitable references for further reading
would be [1, 6]. Variable rate coders have the advantage that less interfer-
ence is generated when the user is generating less information; the reason
why this adds more capacity is detailed in Section 9.4.
The rate at which codecs will improve in future years is far from clear.
At the time that GSM standardization was taking place in the late 1980s,
13-kbps voice coders were available and the view was that soon 6.5-kbps
voice coders of comparable quality would become available. By the late
1990s, such coders were still not available and the trend of rapid reduc-
tion in coding rate seemed to have come to a halt. However, there is still,
in principle, much reduction in coding rates that can be achieved, and
despite the current slowdown in progress, it seems likely that further
advances in speech coding will be found.
2.4.3 Secure transmission
Most analog cellular systems had little in the way of encryption. Anybody
with a scanner able to scan the cellular frequency bands was typically able
to pick up a cellular conversation. Although not initially a problem, even-
tually there were a number of scandals resulting from politicians having
their calls intercepted, culminating in an intercepted phone call from
Princess Diana, the so-called “squidgy” episode. Analog phone systems
also started to experience fraud problems. The earliest of these related to
cloning. Fraudsters with scanners would wait in places where people
were likely to turn on their phones, such as airports. When the phone was
turned on it sent its identity to the base station. The fraudster intercepted
this message and placed the identity of the user’s phone into their own
phone. All the calls the fraudster made were now billed to the original
user, who would not discover this until his or her bill arrived the follow-
ing month. This cloning problem reached epidemic proportions in some
countries. It was obvious to the designers of digital phone systems that
more advanced security was required.
Digital phone systems have security algorithms in place to overcome
the following problems:
◗Encryption, which overcomes eavesdropping of a phone call by an
unauthorized listener;
◗Authentication, which ensures that a mobile cannot be cloned;
46 The Complete Wireless Communications Professional
◗Temporary identities (see Section 2.4.3), which ensure that
eavesdroppers cannot determine the approximate location of a
subscriber;
◗Some systems such as TETRA also have a mechanism whereby the
phone can authenticate the network to ensure that a “dummy” net-
work has not been set up that might prevent the user logging onto
the valid network.
All security mechanisms follow the same basic principle. At the time
of manufacture the mobile (actually the Subscriber Identity Module (SIM)
card in GSM) is given a unique and secret number. This number is only
known to the operator—it cannot be accessed by the user. The secrecy
then resides in keeping this number confidential. When the network
wishes to authenticate a user, it sends him or her a random number. It
sends the same random number to the home location register (HLR; see
Section 3.2), where the secret number is also stored. The HLR combines
the random number with the secret number in a “one-way” algorithm
that produces a particular result. A one-way algorithm is one where it is
relatively simple to calculate the result given the two inputs but almost
impossible to calculate one of the inputs given the other input and the
output. The result is sent to the MSC. The mobile sends the random
number to the SIM, which also returns the result. The result is transmit-
ted back to the mobile switching center (MSC), which compares the two
and, if they agree, authenticates the mobile. Because the random number
will be different each time, even if the exchange of random number and
result is overheard, this is of no use to the would-be cloner. Note that the
random number itself is never sent anywhere, even down wires. This pre-
vents any possibility of interception.
The mobile and the HLR also pass the random number and confiden-
tial number into a different algorithm that is responsible for producing a
mask that is typically a binary string some 64 bits long. The transmitter
then XORs3the user data by this mask in order to derive the transmitted
information. This process is shown in Figure 2.19.
The receiver XORs the received data with the same mask. This results
in the original data being decoded. Since the covert listener does not
know the mask, he or she is unable to decode the data and hence cannot
The basics of mobile radio 47
3. The XOR, or “exclusive OR,” process is one whereby the output is “1” if either, but not
both, of the inputs are “1.”
listen to the conversation. However, even this is not enough. If the mask
remains unchanged for a long enough period of time, it might be possible
to use statistical methods to break the mask. Hence, the mask is derived
from the confidential number, random number, and the frame number,
which increases in GSM each frame (see Section 3.2), around every 6 sec.
As a result, the mask changes sufficiently frequently that statistical meth-
ods will have insufficient information to break the code.
The one-way algorithm Most one-way algorithms work on the
basis of modular arithmetic. The secret code is raised to the power
of the random number, modulo N. So, for example, if the data byte
of the secret code were 2, the random number for that byte 3, and N=7,
then 23=8 and 8 Mod 7 =1. In order to determine the secret code, an
eavesdropper would need to raise the encrypted information to the
power of a decoding code also modulo N. Although the eavesdropper may
know the transmitted result and the random number, calculating the
decoding code for any particular random number is almost intractable if
the random number is sufficiently large. In summary, it is the modular
arithmetic that gives the function its one-way nature since information is
“lost” during the modular operation, leaving the eavesdropper without
the capability to work backward through the function.
2.4.4 Overcoming channel
imperfections
Because of the fading environment explained in Section 2.2 and the pres-
ence of interference, it is rare that a mobile radio transmission is without
48 The Complete Wireless Communications Professional
011001110101
001101101010
00000
1 1 11111
XOR operation
Incoming data
stream
Mask
Output data
Figure 2.19 Multiplication by a mask.
errors. Most radio systems have error rates of around 10−2, or 1 in 100 bits
in error. The simplest way to reduce this error rate would be to increase
the transmitted power such that even in a deep fade there would still be
sufficient signal strength to reliably receive the signal. However, this
would just increase the interference to the next cell, resulting in an
increased error rate in that cell. An alternative, and better, approach is to
add redundancy to the transmitted signal. This has the effect of increasing
the bandwidth required for transmission but allowing the receiver to use
knowledge of the redundancy to remove errors. This tradeoff of band-
width for decreased error rate is the basis of error correction systems. The
best error correction systems are those that provide the greatest reduction
in error rate for the smallest increase in bandwidth. In fact, Shannon’s
theory (see Section 2.6) relates the bandwidth and the signal to noise
ratio and can be used to judge how well error correction systems measure
against the ideal.
There are two different types of error control systems, those based on
block coding and those based on convolutional coding [1]. Both work by
adding extra information to the data to be transmitted and then using a
knowledge of the redundancy in order to correct errors in the original
data. The difference between block and convolutional coding is in the
manner in which the redundancy is added. Block codes add a block of
extra data after the information to be transmitted. Convolutional codes
modify the data itself, adding redundancy in the process.
A typical block code uses a matrix known to the transmitter and the
receiver. The input data is placed in an empty matrix and multiplied by
the agreed matrix. The transmitter then sends the input information and
the result of the matrix multiplication. At the receiver, the received infor-
mation is placed in an empty matrix and the same multiplication per-
formed. The receiver checks for differences between the transmitted
result and the derived result and uses these differences to compute where
the errors are most likely to have occurred. Convolutional codes are
examined in more detail in the next section.
2.4.4.1 Encoding
A diagram of a highly simplified convolutional coder is provided in
Figure 2.20.
The manner in which this encoder works is as follows. The input
datastream is passed into the shift register, with the data being shifted to
The basics of mobile radio 49
the right each time a new input bit is presented. For each time the input is
shifted, two output bits are derived based on the addition (modulo 2) of
the first and third and of the second and third bits. Redundancy is added
into the signal because if the first three inputs had been 111, then these
would be shifted to the right as a new bit arrived, resulting in the encoder
containing either 111 or 011, depending on whether the new bit was a 1
or a 0, respectively. In the case of a 111 input, the output would be 00;
while in the case of a 011 input, the output would be 10. The receiver
could then deduce that if 10 or 11 had been received that an error would
have occurred during the transmission process. By piecing together the
most likely input stream given a particular received waveform and taking
account of the fact that each pair of bits is related to the previous pair, the
receiver can decode a certain number of errors. The optimum way to do
this is by using a Viterbi decoder.4Such decoders are widely used in
mobile radio for error correction, equalization, and reception, and the
concepts of the Viterbi principle and optimal receivers are important
for wireless professionals to grasp. Viterbi decoders are discussed at the
end of this section.
Errors in mobile radio systems tend to arrive in blocks when the
mobile passes through a fade. However, a burst of errors can overwhelm
an error correction system that can only correct a certain number of
50 The Complete Wireless Communications Professional
+
+
Input bits
Output bit 1
Output bit 2
TTT
Figure 2.20 Diagram of convolutional encoder.
4. As an aside, the Viterbi decoder is named after Andrew Viterbi, one of the cofounders of
Qualcomm, a mobile radio equipment manufacturer.
errors in a block of data. This problem is overcome by randomizing the
errors using a device known as an interleaver. This essentially mixes up
the bits before transmission and reorders them on reception. A sequence
of bits in error, when reassembled correctly at the receiver, would then be
more randomly distributed. There are many different ways to mix up
data, some of which have slight advantages over the others. The most
simple to imagine is the block interleaver, shown in Figure 2.21, where
data are fed into the rows in the left-hand matrix until the matrix is full.
They are then fed out in columns to be transmitted. Clearly, they need to
be inserted into the columns in the receiver and the receiver matrix needs
to be full before the rows can be read out, with the data restored to their
original order. Should a burst of errors have occurred during transmis-
sion, then all the bits in one column might have been in error. However,
when reassembled, this will result in one error in each row, a more even
distribution of errors than would otherwise have been the case.
Unfortunately, interleavers introduce delay in the transmission
process because no information can be transmitted until the matrix at the
transmitter is full. Similarly, no information can be read out of the
receiver until the matrix at the receiver is full. In the case of Figure 2.21,
the delay would be equivalent to 72 bit periods because 36 bits need to be
read into the transmitter interleaver before any can be transmitted, and
the receiver must wait for all 36 bits to be transmitted before any decoding
can take place. Adding delay to the speech makes the system sound
increasingly like a satellite link, with the difficulties that humans have in
communicating when there is a long delay, and clearly should be avoided.
There is a difficult balance to be achieved between an interleaver size
(known as the interleaving depth) and the delay that results in the best
The basics of mobile radio 51
123456
7 8 9101112
13 14 15 16 17 18
19 20 21 22 23 24
25 26 27 28 29 30
31 32 33 34 35 36
Read in
by rows
Read out
by columns 1 7 13 19 25 31 2 8 etc.
12
78
13
19
25
31
Read in
by columns
Read out
by rows
Transmitter Receiver
Figure 2.21 Interleaving.
overall speech quality, balancing the adverse effects of delay against the
adverse effects of uncorrected errors.
2.4.4.2 Decoding
If data are convolutionally encoded using an encoder of the form shown
in Figure 2.20 but with a more practical longer shift register, then the bit
sent at any particular point in time is dependent on the bits already in the
shift register. Thus, to decode a particular bit, it is important to have cor-
rectly received the previously transmitted bits so that the contents of the
shift register can be reconstructed and the input data deduced. But the
previously transmitted bits themselves depend on the bits transmitted
previous to that, and so on. Hence, it might be deduced that the optimal
receiver would store the entire received waveform and then find the most
likely transmitted sequence that fits the received waveform. To do this,
the optimal receiver would locally generate every possible sequence of 1s
and 0s that might have been generated by the user, pass them through a
copy of the convolutional encoder used by the transmitter, and compare
the resulting datastream with that received. The sequence of 1s and 0s
that most closely matched the received sequence would then have been
deduced to have been transmitted, with any differences between the
received waveform and the best-fit reconstructed waveform being trans-
mission errors. The input data corresponding to this sequence can then be
output from the receiver as the corrected received data.
The problem with such a decoder is its complexity. For an input mes-
sage length of only 20 bits, the number of possible combinations of mes-
sages is over 1 million (220), and the complexity rises exponentially with
increasing message length. Such an approach is clearly impractical. Vit-
erbi studied this impractical receiver and found that, in practice, it was not
necessary to examine every possible input sequence. To understand the
Viterbi decoder, the encoder shown in Figure 2.20 is used as a very simple
example.
It is normal to represent the receiver as a trellis of possible states, as is
shown in Figure 2.22.
Here the possible states of the encoder (i.e., the bits that could be in
the shift register in the encoder) are down the left-hand side. Because
there are three bits in the shift register, there are eight possible states.
From any given state, it is only possible to go to one of two other
states, depending on whether the new input bit isa0ora1,asshown
52 The Complete Wireless Communications Professional
in Figure 2.22. In this figure, the transmitted data bits (bit 1 and bit 2 in
the encoder diagram) are also shown on the right of the trellis.
Now imagine the coder always starts in the 000 state and look at a
number of input bits. The trellis now starts to look like that shown in
Figure 2.23.
In this figure, the possible paths from a particular starting state (000)
are shown in bold. Now imagine that each of these possible paths was
given a score depending on how close it was to the received data. For
example, in between step 1 and step 2 there are two possible paths, the
first (state 000 to state 000) relating to transmitted data 00 and the second
relating to transmitted data 10. If the received data were 00, then for the
first path the difference between the nominal data and the received data
would be 0 (they are both the same), whereas for the second path the dif-
ference would be 1 (because one of the two bits was different). These
scores are remembered and are attached to the nodes, so the node 000 on
step 2 has a score of 0 and the node 100 has a score of 1. This process con-
tinues between each step, with the score on step 3 equal to the score on
step 2 plus the difference between the received data and the nominal data
for the transition. So, for example, consider the state 100 on step 2.
The basics of mobile radio 53
000
001
010
011
100
101
110
111
00
11
01
10
10
01
11
00
Figure 2.22 The start of a trellis diagram.
Transitions to states 010 and 110 are allowed relating to transmission of
01 and 11, respectively. Say the received data were 00, then node 010
would have a score of 2 (because node 100 had a score of 1 and the differ-
ence is 1) and node 110 would have a score of 3 (difference of 2).
A key point is reached at step 5. Here, two paths converge into each
state (only those converging into state 000 have been shown for clarity).
Viterbi said that whichever paths are followed into the future from state
000, they will always select as their tail the path entering state 000 with
the lowest score. Hence, whenever two paths converge, the scores for
each path are calculated and the path (or paths in the case of more com-
plex encoders) with the highest scores are discarded. So for each node in
the trellis, it is only necessary to remember the score at that point and the
incoming path relating to that score. Viterbi found another key point. If
the highest score paths were discarded, then at any particular point, if the
step in the trellis say 20 steps prior to that currently being processed was
examined, all the current valid paths at the current step would typically
pass through only one state this far back in the trellis. Viterbi found from
experimentation that this point was around 7 times the constraint length
in steps back from the current point, where the constraint length broadly
54 The Complete Wireless Communications Professional
000
001
010
011
100
101
110
111
00
11
01
10
10
01
11
00
00
11
01
10
10
01
11
00
00
11
01
10
10
01
11
00
00
11
01
10
10
01
11
00
00
11
01
10
10
01
11
00
00
11
01
10
10
01
11
00
Step
1234567
Figure 2.23 The trellis becoming more complete.
relates to the number of bits in the shift register (e.g., three in the case of
this example).
These discoveries dramatically simplified this optimum form of
decoding. Instead of having to trace millions of paths, only 2c, where cis
the constraint length, paths need decoding at any point, and only 2c×7c
pieces of data need to be remembered (168 in the case of this example).
This is still not trivial, but a massive improvement on the previous optimal
detection. Remember that the Viterbi approach is still optimal in that it
compares the received data with every possible piece of transmitted data
over a large number of bits in order to deduce the most likely received
output.
The form of Viterbi decoding just described is often called “hard
decoding” because the received data are quantified toa1ora0prior to
the Viterbi decoding process. This is not essential; unquantified received
items of data such as 0.83 could be input into the decoder. This increases
the complexity slightly because more memory is required to remember
the noninteger scores, but better performance is typically achieved as a
result.
The decision of whether to use a Viterbi decoder is always difficult. It
is an optimal decoder and so by definition generates the best results. How-
ever, it also has much greater complexity than nonoptimal decoders. The
decision typically depends on the number of states in the encoder.
The complexity of the Viterbi decoder rises exponentially with the
number of input states whereas the complexity of most other decoders
rises only linearly. Hence, as the encoder becomes increasingly large, the
Viterbi decoder becomes less likely to be selected due to its complexity.
2.4.5 Frequency and phase
modulation
After having undergone the process described in the previous sections,
there is an encoded and error-corrected digital data stream consisting of
square-wave binary pulses. If such a waveform were transmitted directly,
then it would use vast amounts of spectrum. Fourier transform theory
shows that an instantaneous change in the time domain (e.g., the rising
edge of a binary pulse) requires an infinite amount of bandwidth in the
frequency domain. Something more needs to be performed before the
signal can be transmitted, and this is the process of modulation and pulse
shaping.
The basics of mobile radio 55
Modulation is typically divided into three classes:
◗Phase modulation (PM), where the phase of the carrier waveform is
changed depending on the information to be transmitted;
◗Amplitude modulation (AM), where the amplitude of the carrier
waveform is changed depending on the information to be
transmitted;
◗Frequency modulation (FM), where the frequency of the carrier wave-
form is changed depending on the information to be transmitted.
Frequency and phase are closely related: an increase in the frequency
of a wave will result in a change in the phase for a receiver whose refer-
ence frequency does not change. Similarly, a change in the phase will
result in a short-term change in the frequency. Because of this close rela-
tionship, frequency and phase modulation can be considered as part of
the same class of modulation waveforms. Examples of waveforms for
phase and amplitude modulation when an analog signal is transmitted
are shown in Figure 2.24. Typically, phase modulation is less susceptible
to interference and is more widely used.
In the case of digital transmissions, the modulated waveforms are
shown in Figure 2.25.
Here it can be seen that there is an abrupt transition between the dif-
ferent states as the modulating data change. Such abrupt transitions cause
the transmitted spectrum to become much broader, increasing the inter-
ference to other users.
Improvements can be made in the use of phase modulation if mini-
mum shift keying (MSK) is adopted. In MSK the phase of the signal is
advanced or retarded by 90 degrees over the symbol period, typically
in a linear manner. This avoids the sharp changes in phase shown in
Figure 2.25. A more advanced category of phase modulation is Gaussian
MSK (GMSK), where instead of the phase varying in a linear fashion over
the symbol period, the rate of change is limited with a Gaussian response.
The bandwidth of the transmitted waveform for simple binary phase shift
keying (BPSK) is shown in Figure 2.25(d); MSK and GMSK are shown in
Figure 2.26.
In this figure, the stylized and simplified transmitted power is shown
at the carrier frequency (represented as 0 on the x-axis) and at increasing
frequency deviations from the carrier, where the bandwidth of the
56 The Complete Wireless Communications Professional
The basics of mobile radio 57
(a)
(b)
(c)
(d)
Figure 2.24 (a) Carrier waveform, (b) modulating waveform,
(c) amplitude modulated waveform, and (d) frequency modulated
waveform.
58 The Complete Wireless Communications Professional
−1.5
−1
−0.5
0
0.5
1
(a)
1.5
−1.5
−1
−0.5
0
0.5
1
1.5
−0.5
0
0.5
1
1.5
−1.5
−1
−0.5
0
0.5
1
1.5
(b)
(c)
(d)
Figure 2.25 (a) Modulating waveform, (b) amplitude modulation,
(c) frequency modulation, and (d) phase modulation.
baseband signal is 1. An ideal modulation scheme would result in the sig-
nal falling below −100 dB at a frequency deviation of 1. From Figure 2.26,
the very poor performance of BPSK is clear with the signal only falling to
−20 dB around 2.5 times the bandwidth from the carrier. MSK is signifi-
cantly better with GMSK, providing slight gains over MSK.
Pulse shaping Another way of looking at approaches to reducing the
transmitted bandwidth such as GMSK is as a filtering process in which the
input pulses are passed through a filter before being modulated with a
basic PM technique. This is termed pulse shaping. The square pulses are
passed through a filter, resulting in rounded pulses. The more severe the
filter, the lower the bandwidth of the transmitted signal, but the more the
difficulty in decoding the signal. Depending on the bandwidth scarcity,
such tradeoffs need to be made by the system designer.
A set of widely utilized filters is the so-called raised-cosine (RC) filters,
which modify the ideal square low-pass filter response by placing a quar-
ter period of a cosine-shaped curve on both the vertical transitions, as can
be seen in Figure 2.27. The bandwidth is controlled by the so-called roll-
off factor , defined as the ratio of excess bandwidth above the perfect filter.
The RC characteristic is then defined as
()
()
Gf T f T
Gf TT
fT
=≤≤
−
=− −
for 0 1
2
211
2
α
π
α
sin
−<≤
+
for 1
2
1
2
αα
TfT(2.8)
The basics of mobile radio 59
−80
−60
−40
−20
00
Signal strength (dB)
0.5 1 1.5 2 2.5 3
Frequency deviation (1 bandwidth)=
BPSK
MSK
GMSK
Figure 2.26 The comparative performance of BPSK, MSK, and
GMSK.
where αis the roll-off factor that controls the severity of the filter and
T=1/2fis a measure of the bandwidth of the signal to be transmitted.
Figure 2.27 shows the filter response for a range of different roll-off
factors.
An optimal filter would be one with α= 0, where there would be no
interference into adjacent channels. However, such a filter is impossible
to achieve and would result in the input pulses, when viewed in the time
domain, being spread over an infinite period. Coupled with each of the
frequency responses shown in Figure 2.27 is a corresponding time
domain, or impulse response, that shows how the input pulses are spread
over time. The higher the value of α, the less the pulses are spread in the
time domain.
The impulse response of the RC characteristic plays an important role
in deciding upon the choice of in a particular system. Namely, when the
channel becomes nonideal and, hence, the ISI is nonzero, the decay of the
impulse response must be as rapid as possible to minimize the duration
over which a previous transmitted symbol can influence the received sig-
nal. In summary, lower roll-off factors yield spectral compactness, but
they are also more vulnerable to ISI via nonideally equalized channels.
This makes clock recovery much more difficult to achieve.
It is possible to extend the impulse response of the filter over more
than the duration of one symbol period. This allows a compact frequency
response that does not need large guard bands between radio channels
but “smears” the information in one pulse into the next pulse. Such a
technique is called partial response signaling. The effect for the receiver is
60 The Complete Wireless Communications Professional
0
Response
0.2
0.4
0.6
0.8
1
1.2
−1.00 −0.60 −0.20 0.20 0.60 1.00
Frequency
alpha 0=
alpha 0.5=
alpha 1=
Figure 2.27 Filter response for a range of roll-off factors.
identical to ISI and requires the use of an equalizer, as discussed in
Section 2.4.4, to recover the original data. In modern radio systems,
added complexity is a small price to pay for increased spectrum efficiency
and, hence, systems such as GSM spread input pulses over three symbol
periods to reduce the transmitted bandwidth. Such partial response filters
are often categorized by their bandwidth-time (BT) product, where the
product is given by 1 divided by the number of symbols across which the
data are spread. A system with a BT product of 1 only spreads the input
pulses over one symbol period, whereas a system with a BT product of
0.33 spreads the input pulses over 3 symbol periods. GSM uses a BT prod-
uct of 0.3. One of the most normal uses of partial response filters is
with GMSK, where the Gaussian response is modified according to the
required BT value. Figure 2.28 shows the performance of GMSK with a
range of different BT values.
The gains in performance from using a smaller value of BT are clear.
However, while a system with a BT =1 would not require an equalizer to
decode the modulation, one with BT =0.5 would require an equalizer
operating over 2 symbol periods and one with BT =0.3 over 3.3 symbol
periods (in practice, this would mean over 4 symbol periods). If the opti-
mal Viterbi equalizer is used, the relative complexity of the three schemes
would be 1, 4, and 16 for BT =1, 0.5, and 0.3, respectively.
Quadrature modulation In order to encode more bits of information
into the same radio spectrum, both the amplitude and the phase can
be changed simultaneously, with some bits of the input information
being encoded onto the amplitude and others onto the phase. This is
The basics of mobile radio 61
−100
0 0.5 1 1.5 2 2.5 3
Frequency deviation
BT 1=
BT 0.5=
BT 0.3=
−80
−60
−40
−20
0
Signal strength (dB)
Figure 2.28 Comparative performance of GMSK with different BT
values.
termed quadrature amplitude modulation (QAM) because the amplitude is
being varied on both the in-phase and quadrature arms of the modulating
waveform. Broadly, the advantage of QAM is that more information is
encoded for the same spectrum. The disadvantage is that a greater signal-
to-noise ratio (SNR) is required. On twisted pair cables, a high SNR is avail-
able and so QAM is a natural choice; whereas with mobile radio, a low
SNR is typically experienced and hence QAM cannot be simply deployed.
A typical QAM constellation is shown in Figure 2.29, where the I- and
Q-axes represent the in-phase and quadrature modulation of the carrier,
respectively. The in-phase wave is that modulated using a sine wave,
while the quadrature wave is that modulated using a cosine wave. Both of
these waves can be modulated onto the same carrier simultaneously
because they are orthogonal; that is, the presence of one does not affect
the data carried on the other. A particular point on the constellation of
Figure 2.29 is transmitted via suitable amplitudes of the in-phase and
quadrature waves. The result can also be considered to be a vector or pha-
sor with a particular amplitude (the length of the vector) and a particular
angle (the angle of the vector relative to the I-axis). Both representations
are interchangeable.
The apparent advantage of QAM is that, having a constellation with
more points than the two used in binary in-phase modulation (known as
BPSK) or the four used in quadrature single amplitude modulation
(known as QPSK) as shown in Figure 2.30, more bits of information can
be transmitted on each symbol. A symbol is the information transmitted
during one modulation period; this information can include more than
one bit of information in the case that there are more than two potential
modulation states. In the case of Figure 2.29, four bits per symbol can be
transmitted compared to one for BPSK and two for QPSK (hence the rea-
son for the term ISI rather than interbit interference because there can be
more than one bit per symbol). It might seem that QAM was advanta-
geous because of this capability to carry more information. However, this
is not true in mobile radio. Because the points in a QAM constellation are
closer together than in a QPSK constellation, the signal needs to be
received with less noise in order to be correctly decoded. In dense mobile
radio networks, most of the noise is cochannel interference, generated
from nearby cells using the same frequency. The net result is that QAM
systems need to work with a larger cluster size than QPSK systems. The
increase in cluster size more than offsets the gain in the number of bits per
symbol, with the result that QAM systems tend to have a lower overall
62 The Complete Wireless Communications Professional
spectrum efficiency. This was proved rigorously in [7] and, hence, it
seems unlikely that QAM will be widely used for cellular. Even in the
world of WLL, where cochannel interference is less severe as a result of
the directional antennas used, QAM has been shown not to be advanta-
geous [4]. Only in fixed communications, where there is no cochannel
interference, is QAM suitable. Those interested in finding out more about
this form of modulation should refer to [8].
Other types of modulation There are many other variants of modu-
lation that are typically used with quadrature transmission to overcome
the problems caused when a transition from one symbol to another
The basics of mobile radio 63
In-phase axis
Quadrature axis
In-phase axis
Quadrature axis
Binary Phase Shift Keying
Quadrature Phase Shift Keying
Figure 2.29 BPSK and QPSK constellations.
causes the modulating signal to cross the origin of the constellation dia-
gram. This would require the transmitted signal to fall momentarily to
zero, resulting in full amplitude modulation of the carrier. If the amplifi-
ers used are not linear, the transition through zero is likely to result in dis-
tortion and a broadening of the transmitted spectrum. Techniques to
overcome this problem include π/4 QPSK and offset QPSK (O-QPSK). In
π/4 QPSK the constellation points “rotate” by 45 degrees each symbol
period, preventing any transition from passing directly through the ori-
gin. In O-QPSK the transition in the Q-axis is delayed by half a symbol
period to the transition in the I-axis, again preventing a transition
through the origin. These forms of modulation are discussed in more
detail in [8].
2.4.6 Clock recovery
It is important that both the transmitter and the receiver are synchronized
because otherwise the receiver does not know when to sample the
incoming waveform nor with what to compare any change in phase of
the incoming waveform. Receivers may require both clock and carrier
recovery systems that both attempt to derive information about tim-
ing from the received signal, often in a similar manner. While carrier
64 The Complete Wireless Communications Professional
In-phase axis
Quadrature axis
Figure 2.30 A typical QAM constellation.
recovery is only necessary in coherent demodulation systems (which do
not use differential coding), clock recovery is required in all schemes, and
accurate clock recovery is essential for good data transmission. Confusion
often exists between clock and carrier recovery. Clock recovery attempts
to synchronize the receiver clock with the baseband symbol rate trans-
mitter clock, whereas carrier recovery endeavors to align the receiver
local oscillator with the transmitted carrier. In this section a brief review
of some of the more widely used clock recovery schemes is provided while
carrier recovery schemes are considered in the next section. More details
can be found in [8].
There exist a number of different clock recovery techniques. How-
ever, many apparently different clock recovery techniques can be shown
to be equivalent, and this is not surprising since they must all make use
of the properties of the received waveform. Basic clock recovery sys-
tems include times-two, early-late, zero-crossing, and synchronizer clock
recovery systems.
Times-two clock recovery The most fundamental of all clock
recovery schemes is the times-two, or squaring system. If the received
demodulated signal is squared, then it will possess a periodic component
at the symbol rate. A bandpass filter tuned close to the symbol rate
will extract this periodic signal, allowing derivation of the required
timing information. The times-two clock recovery works best for binary
modulation schemes, but not so well for multilevel ones. The reason for
this is that the multilevel scheme has a reduced component at the
symbol frequency due to the increased possibility of non-zero-crossing
transitions.
Early-late clock recovery Another well-known form of clock recov-
ery is early-late clock recovery. While times-two clock recovery exploits
the whole of the incoming waveform, early-late clock recovery works on
the peaks in the received waveform. The basic assumptions made by the
early-late method are that the peaks in the incoming waveform are at the
correct sample point and that these peaks are symmetrical. This is often
true, but for some modulation schemes, such as partial response RC,
neither of these assumptions is valid. It may still be possible to use early-
late clock recovery with these modulation schemes, but the timing
jitter will be increased. The early-late scheme first squares the incom-
ing signal to make all peaks positive and then takes two samples of
the received waveform, both equispaced around the predicted sample
The basics of mobile radio 65
point. If the predicted sample point is aligned with the correct sam-
ple point and the previous assumptions are correct, then the sample taken
just prior to the sample point—the early sample—will be identical to the
sample taken just after the sample point—the late sample. If the early
sample is larger than the late sample, this indicates that the recovered
clock is sampling too late, and if the early sample is smaller than the late
sample, this indicates that the recovered clock is sampling too early. It is
normal to filter the difference of each pair of samples to reduce the effect
of random noise on the system.
Zero-crossing clock recovery Similar to early-late clock recovery in
that it looks for a specific feature in the received waveform, is zero-
crossing clock recovery. This works on the premise that with symmetrical
pulses, the received waveform will pass through zero exactly midway
between the sample points. The receiver detects a change in the polarity
of the received signal and, if this does not occur midway between pre-
dicted sample points, speeds up or slows down its reconstructed clock
appropriately.
Synchronizer clock recovery A completely different clock recovery
system is the synchronizer, which is the scheme used by GSM. In this sys-
tem the transmitter periodically sends a sounding sequence, for which
the receiver searches by performing an auto-correlation at a rate signifi-
cantly faster than the symbol rate (normally four times faster). The over-
sample point at which the maximum correlation occurs is taken to be
the correct sample point and is assumed to remain correct until the
next sounding sequence is received. This scheme is simple but requires
a sounding sequence to be periodically inserted into the datastream,
increasing the bandwidth requirements. It also requires that the transmit-
ter and receiver clocks do not drift significantly over a block, which may
place constraints on the circuitry that can be employed. Synchronization
has the advantage that it performs well regardless of the modulation
scheme in use.
2.4.7 Carrier recovery
Carrier recovery is required when coherent detection is used. Coherent
detection requires the receiver to determine the absolute phase and
amplitude transmitted. The alternative to coherent detection is to use dif-
ferential coding. In this case, the transmitted information is encoded as
66 The Complete Wireless Communications Professional
the difference between the previous symbol and the current symbol. The
receiver can decode this information by comparing the previous and cur-
rent symbols and, hence, does not need to understand the absolute phase
or amplitude transmitted. Differential coding is widely used because of
the simplification in the receiver architecture but has the disadvantage
that two errors are generated when only one error would be generated
with coherent detection. These two errors result because if one symbol is
received in error, there will be a resulting error when decoding the differ-
ence between it and the previous symbol and between the next symbol
and this symbol. This additional 3-dB penalty is a serious price to pay for
resulting simplicity. For a more detailed discussion of when to adopt
coherent and noncoherent detection, see [4].
A common problem for most carrier recovery schemes is an inability
to resolve phase ambiguities. So for constellations such as QPSK, phase
lock can be established at all multiples of 90 degrees (because it is not pos-
sible to determine the phase change imposed by the propagation chan-
nel), but without additional transmitted information it is not possible to
resolve the angle at which phase lock has been established. This problem
can be overcome by sending a sounding sequence or via the use of differ-
ential coding. Some of the more common carrier recovery systems are
summarized next.
Times-ncarrier recovery As with clock recovery, a common form of
carrier recovery for binary schemes is the times-two or the squared carrier
recovery. In this scheme the incoming carrier wave is squared, leading to
a periodic component at the carrier frequency that can be isolated using a
filter and phase locked loop. This scheme can only work with binary
modulation.
Decision-directed carrier recovery A carrier recovery system that
is completely different from all the carrier and clock recovery systems
discussed so far is decision-directed carrier recovery. In fixed link sys-
tems this has proved to be one of the most popular carrier recovery
schemes. In this scheme, a decision is made as to which was the most
likely constellation point transmitted given the received symbol. This
is normally the constellation point closest to the received symbol, as
shown in Figure 2.31. It is then assumed that the phase difference
between the received symbol and the constellation point is due to carrier
recovery drift; the receiver carrier recovery is updated accordingly.
The basics of mobile radio 67
Decision-directed carrier recovery has the advantage that it can work
with all modulation schemes. Decision-directed methods normally have
an associated bit error rate (BER) threshold. If the BER is less than this
threshold, then such methods operate extremely well since they effec-
tively remove noise on the input phasor. If the BER is more than this
threshold, then catastrophic failure can result whereby the constellation
point selected in the receiver is the wrong one. The update signal to the
carrier recovery system is therefore wrong, driving the carrier further
from the correct frequency and further increasing the chance of error.
Whether decision-directed carrier recovery will be suitable will depend
on this BER threshold, which itself is dependent on the modulation
scheme and the quality of the radio channel.
2.4.8 Multiple access
Multiple access techniques have become a key topic as a result of the
CDMA/TDMA debate discussed in Chapter 14. The selection of multiple
access method has some important implications that are discussed in
more detail in this section.
There are three key multiple access techniques:
◗Frequency division multiple access (FDMA), where the total spectrum
assignment is divided into a number of discrete frequencies;
◗Time division multiple access (TDMA), where the total spectrum is
divided in time between a number of users;
68 The Complete Wireless Communications Professional
In-phase axis
Quadrature axis
Allowed transmitted pointsPoint actually
received
Angular difference to nearest allowed
point which is assumed to be the error
in the recovered carrier
Figure 2.31 Decision-directed carrier recovery.
◗Code division multiple access (CDMA), where neither the frequencies
or the time are divided but users are distinguished through the use
of a special code.
Many other multiple access techniques have been suggested,
although most are used in combination with one of the aforementioned
three approaches rather than on their own. Worthy of note is packet reser-
vation multiple access (PRMA), where the mobile waits until their user is
speaking and then reserves a channel by sending a random access mes-
sage. When the user stops speaking, the channel is returned to the pool.
PRMA is efficient in that channels are only used when users are speaking,
but there is a risk that a channel is not available when a user starts speak-
ing, resulting in “clipping” of the speech. For this reason, PRMA is not
used in any voice-based mobile radio systems. Space division multiple access
(SDMA) uses directional antennas at the base stations that follow mobiles
using beam-forming technology. The narrow antenna beamwidth means
the same frequency can be reused in the same sector if the two mobiles
are far enough apart. The difficulty with SDMA is the complexity of
beam-forming antennas, but these are expected to become feasible in the
near future; indeed, there is already a number of manufacturers offering
“smart antenna” products.
Each of the three key multiple access methods is now described in
more detail.
FDMA FDMA is the simplest of all access techniques to understand and
is the most widespread multiple access technique in use today. The total
spectrum allocated to an operator is divided up into a number of equal
channels and each user who requires access to a channel is given one of
these frequencies for the duration of their call. This is shown symbolically
in Figure 2.32. FDMA has been widely deployed because of the simplicity
of building FDMA systems. An FDMA mobile needs a transmitter and
receiver that can be moved to any given frequency within the assigned
band and a filter arrangement that can filter out the unwanted
transmissions.
FDMA is a relatively inefficient scheme. It is very difficult to con-
struct a transmitter that keeps all radiated energy within the frequency
band assigned, as was shown in the discussion on pulse shaping in
Section 2.4.5. The figures in that section showed that substantial energy
was transmitted in the frequency bands used by other mobiles, and
The basics of mobile radio 69
Figure 2.33 shows that this is so even in the relatively advanced GSM sys-
tem. To overcome this problem, two techniques are adopted. The first is to
insert a “guard band” between each frequency to increase the frequency
separation between transmissions. The second is to avoid using adjacent
frequencies in the same cell. Because, typically, only around 1 in 20 fre-
quencies can be used in any cell with FDMA due to the cluster effect, this
latter constraint is not unduly problematic.
A cost disadvantage for FDMA results from the need for each individ-
ual radio channel to pass through a separate power amplifier at the base
70 The Complete Wireless Communications Professional
Frequency
Power
Figure 2.32 An ideal FDMA spectrum.
−80
−70
−60
−50
−40
−30
−20
−10
0
kHz
−500
500
−400
400
−300
300
−200
200
−100
100
0
dB
Figure 2.33 GSM spectrum.
station before passing through an expensive high-power combiner and
then being transmitted from the antenna. Alternatively, FDMA signals
could be combined prior to amplification, but this would require a highly
linear amplifier that would be expensive and inefficient in its use of
power.5
As will be seen, all the access methods have inefficiencies and FDMA
is not substantially worse than TDMA. However, the extra cost is signifi-
cant, and with the widespread deployment of mobile radio systems,
FDMA has been used minimally since the early 1990s.
TDMA The rational with TDMA is that if a user is given access to a
wider bandwidth than He or she requires, then he or she will only need to
transmit for part of the time. During the remainder of the time, other
users can transmit their information. To work, TDMA requires precise
timing between the transmitter and the receiver so that each user
transmits during the time allocated to him or her. It requires a framing
structure to separate different users, and it requires that the time between
the same user making his or her current and next transmissions is
sufficiently small so that unacceptable delay is not added to any speech
transmission. The most successful TDMA system is GSM, where each user
has access to the channel for 577 µs every 4.6 ms, allowing eight users on
the same channel.
TDMA also has guard bands between transmissions. In the case of
TDMA, the guard bands are gaps in time between one user stopping trans-
mission and the next user starting. These guard bands are required both to
accommodate inaccurate timing and to allow the mobile some time to
“ramp up” power levels and to ramp them back down again. Such a ramp-
ing of power is required since otherwise the instantaneous change from
no transmission to full transmission would be akin to sending a square
pulse, which, as was explained in Section 2.4.5, results in substantial
interference to neighboring frequency bands. The structure of a TDMA
burst in GSM is shown in Figure 2.34. A burst consists of a ramp-up
period, a longer period of transmission, and a ramp-down period. One
mobile ramps up while another ramps down, so the inefficiency is limited
to one of the two ramping periods. Hence, around 30 µs is “wasted” for
each 540-µs transmission period.
The basics of mobile radio 71
5. Note, however, that such amplifiers are starting to become more common since their use
may be required in TDMA systems operating in more than one band, which is likely to
drive down their cost over time.
A further problem with TDMA is caused by the fact that the rate of
transmission is raised well above that required for FDMA. As explained in
Section 2.2, higher transmission rates can result in ISI, which then
requires an equalizer to remove the ISI. In turn, this requires the trans-
mission of a sounding sequence, reducing the user data that can be
transmitted.
Nevertheless, TDMA is significantly less expensive than FDMA to
deploy because it overcomes the need for a separate amplifier for each
user. Instead, a separate amplifier is required for each TDMA channel,
which can support a number of users. Indeed, the same decoding cir-
cuitry, equalizer, and error-correction unit, for example, can all be used
on one TDMA channel because only one user can transmit at the same
time. It is because of these cost savings that TDMA was selected for GSM.
CDMA With CDMA, each user transmits across all the allocated spec-
trum for all the time. In order to fill all the allocated spectrum, they need
to increase the amount of information they transmit substantially and
they do so by multiplying the user data by an assigned code. It is the
redundancy provided by this code that allows the signal from a particular
user to be decoded amongst all the interference being generated by the
other users transmitting at the same time and on the same frequency. The
process of multiplication by a codeword is known as spreading and
72 The Complete Wireless Communications Professional
30 sµ540 sµ30 sµ
−70
Time
Level dBm
−30
+1
Figure 2.34 GSM ramping up for a burst.
is shown for an example datastream and codeword in Figures 2.35
and 2.36.
The number of bits in the code assigned to the user will determine the
bandwidth of the transmitted signal. In practical CDMA systems, code-
words of 64 bits in length are used resulting in the user data taking up
64 times more spectrum than if it were transmitted using FDMA. The
length of the codeword is often represented by the letter G. If the number
of bits is reduced, then less spectrum is required but less redundancy is
The basics of mobile radio 73
Input
speech Speech
coder
Spreading
code Carrier
frequency
Antenna
Transmitter—the spreading or coding process
Receiver—the despreading process
Output
speech
Speech
decoder
Spreading
code
Carrier
frequency
Antenna
Figure 2.35 Process of spreading.
added. Larger codewords result in a higher transmitted bit rate that
brings the advantage of being able to better resolve multipath although at
the expense of the operator requiring a larger spectrum assignment. Mul-
tipath can be better resolved because, as discussed in Section 2.2, multi-
path propagation results in fading if the delay on the other paths is less
than a symbol duration and results in ISI if it is longer. Fading cannot be
mitigated, but ISI can be removed by an equalizer. By using a higher bit
rate, any multipath propagation becomes more likely to be ISI rather than
fading; hence, the overall propagation is improved, albeit at the expense
of requiring a more complex equalizer.
The choice of the code is critically important. The code should
have certain auto-correlation properties. Auto-correlation is effectively
the multiplication of a code by itself when one copy of the code is
delayed relative to other copies. Taking a random code of, say,
−1,1,1,−1,1,−1,1,1,−1,1,−1,1, the process of auto-correlation can be
examined. Multiplied by itself with no time shift for the second copy, the
result is
First copy −1−1−1−1−1−1−1−1−1−1−1−1
Second copy −1−1−1−1−1−1−1−1−1−1−1−1
Result −1−1−1−1−1−1−1−1−1−1−1−1=12
Now shifting the second copy by one bit to the right, the result is as
follows:
First copy −1−1−1−1−1−1−1−1−1−1−1−1
Second copy −1−1−1−1−1−1−1−1−1−1−1−1
Result −1−1−1−1−1−1−1−1−1−1−1−1=−8
74 The Complete Wireless Communications Professional
User data waveform
Spreading waveform
Resultant waveform
Figure 2.36 Result of spreading.
This process can be continued for all possible shifts, in this case of ±6
bits from the case where the codes are aligned. The results can be seen in
Figure 2.37, where the vertical axis shows the result while the horizontal
axis shows the shift from the aligned position.
As can be seen, the largest peak is at zero offset and the result is sym-
metrical about the origin. Such an autocorrelation would not be suitable
for CDMA because some of the results (at, e.g., 5 shift) are almost as great
as the result at zero shift. A more suitable autocorrelation curve for
CDMA is shown in Figure 2.38, where a large result is obtained only at
zero offset.
Many families of codes with such autocorrelation properties are
known; for example, Gold codes, named after their discoverer, exhibit
such properties.
CDMA signals are recovered by multiplying the received signal,
which is the additional of all the signals sent by each of the users, by the
code assigned to a particular user. As explained in Section 2.4.3 on
encryption, such a double multiplication by the same code results in the
original signal being detected. This process within the receiver is known
as despreading and results in the wanted signal being enhanced by a fac-
tor equal to the codeword length, G. It is this enhancement that raises the
level of the signal above the noise generated by the other users and allows
it to be correctly decoded. A more detailed example of how despreading
occurs can be found in [9].
The process of despreading can only isolate the wanted signal from
that transmitted by the other users if they have different codes. Indeed,
The basics of mobile radio 75
−10
−5
0
5
10
15
Magnitude
Timeshift
−6−5−4−3−2−10123456
Figure 2.37 The result of autocorrelating –111-11-111-11-11.
for CDMA to work perfectly, the codes that they use must all be orthogo-
nal6to that used by the wanted transmission. In the case that the codes
are orthogonal, when the composite received signal is despread, the sig-
nal from the wanted user is enhanced by the factor G, whereas all the
other signals are neither enhanced or suppressed. If the codes were differ-
ent but not orthogonal, then the multiplication process would also
enhance some of the data from the other users, making it more difficult to
distinguish the data from the wanted user. There are a number of code
families that are orthogonal, of which the best known is probably the
Walsh family. However, in any one family there can only be as many
orthogonal codewords as there are bits in the codeword, that is, G. For
more information about codes see [3, 10].
Although in an isolated cell Gcodes would be sufficient because only
Gusers can be accommodated in any case, the shortage of codes becomes
a problem in a network with overlapping cells. If the same frequency is
used in each of these cells, then it is quite possible that more than Gusers
could be accommodated across the entire cluster were there enough
codes. If only orthogonal codes were employed, the capacity of the total
network would be restricted to G/K, where Kis the cluster size that would
be required to avoid interference between users deploying the same code.
In practice, Kwould probably need to be around 12; hence, with G=64 (a
typical value) only five users could be accommodated per cell. This
problem is overcome using nearly orthogonal code families such as the
76 The Complete Wireless Communications Professional
−5
0
5
10
15
−6−5−4−3−2−10123456
Magnitude
Timeshift
Figure 2.38 A more suitable autocorrelation curve for CDMA.
6. Codes are said to be orthogonal if when the two codes are multiplied by each other, the
result is zero. For more details about the basic mechanism of coding and decoding,
see [1].
pseudorandom noise (PN) codes. In such families there is no shortage of
codes, but the interference from other users becomes slightly more
problematic.
The use of nearly orthogonal codes also raises a further problem.
Because the codes are not orthogonal, some component from other users
will be decoded during the despreading process. This may not be problem-
atic when the transmissions from all users are received with the same
strength, but if the signal strength from another user is significantly
greater than that from the wanted user, then the decoded component
from the unwanted user could be greater than the decoded component
from the wanted user. To overcome this problem, transmissions from all
the users in a cell need to be received at nearly the same signal level. (This
is not an issue in the downlink direction because all the signals are sent
from the same point and so remain at the same relative signal strength.)
However, as the mobile moves around the cell, the propagation channel
changes rapidly, requiring the mobile to rapidly change its transmitted
power levels to keep the received signal at a constant level. This is known
as power control.
Power control systems need to be extremely accurate. If a mobile
transmits with too much power, it results in excessive interference to all
the other mobiles and hence a loss in capacity. If one mobile transmits
with twice the power it should have, it can halve the overall system
capacity. Maintaining the correct power is difficult since the propagation
environment changes rapidly and the mobile needs to adjust to these
changes every millisecond. Some simulated results showing how the sys-
tem capacity is expected to change with increasing error in the power
control system in the mobiles are shown in Figure 2.39.
The basics of mobile radio 77
0
20
40
60
80
100
Error (dB)
0 0.5 1 1.5 2 2.5 3 3.5 4
Capacity (%)
Figure 2.39 Sensitivity to power control error in CDMA systems.
Designing good power control systems is difficult. The systems tend to
be combinations of open loop and closed loop systems. The mobile gets its
first pass estimate of the path loss to the base station from its received sig-
nal. However, because the downlink may be experiencing different fast
fading from the uplink, the first pass estimate will only be approximate.
The mobile transmits at this appropriate power level based on this first
pass estimate and then lets the base station provide closed loop informa-
tion to achieve accurate power control. The base station sends the mobile
periodic signals instructing it to either increase or decrease its power in
order to reach the appropriate transmission level. Although necessary to
ensure correct system operation, sending such signals is undesirable
because they waste radio spectrum. The more frequently the messages
are sent, the more accurate the power control will be. Similarly, the more
bits in the message, the more steps there can be in power control; but the
more messages, the greater the waste of radio spectrum. In practice, simu-
lations have shown that short frequent messages achieve the best results
and, hence, most CDMA systems transmit just one bit (indicating either a
small increase or decrease in the transmission levels) at a rate of over
1,000 times a second.
In fact, accurate power control would require that the mobile
transmit power follow exactly the fast fading environment. As seen in
Figure 2.4 this would require extremely rapid changes in power. Such
rapid change is typically not possible, and hence, the transmit power con-
trol only follows the slow fading and distance related fading. Given that
some fast fades are 40-dB deep, the mobile power control could be 40 dB
out. Fortunately, in fades the mobile transmits with too little power,
resulting in a higher error rate but less interference. However, the fading
channel can result in signals around 6 dB higher than average at times
and, during this period, the mobile will be generating excess interference.
Hence, this is the reason why highly accurate power control is difficult to
achieve.
Within the mobile community, there has been much impassioned
discussion about whether TDMA or CDMA represents the best access
technique. This issue is discussed in more detail in Section 14.4. How-
ever, it is becoming increasingly clear that selecting appropriate fixed
networks and technologies with economies of scale and widespread
deployment is becoming more important than selecting the best access
technique.
78 The Complete Wireless Communications Professional
2.5 Packet and circuit
transmission
Transmission of data can be divided into two different types. With
circuit-switched transmission, the user requests a transmission resource
(such as a TDMA channel) for the whole of the conversation and returns
this channel once the conversation has been completed. The transmission
resource is known as a circuit. Circuit-switched transmission has the
advantage of simplicity, but the disadvantage that even when nothing is
being said, nobody else is able to use the channel. It also, typically, takes
some time to establish a circuit, which can be disadvantageous when the
amount of information to be transmitted is small. This can result in the
channel being used for a time period that is the sum of the setup time and
the transmission time despite the fact that the transmission time is rela-
tively short.
A solution to these problems is to use packet switching. In a packet-
switched system, the user fills up a buffer at the transmitter. When this is
full, a resource is requested from the network for the transmission of this
single packet. The packet is then dispatched along with address informa-
tion and is forwarded through the network until it reaches its destination.
Because the user does not generate any information when he or she is not
speaking, no packets are filled and no transmission resource is required.
Further, should the user want to send more information for some reason
(perhaps they want to send a data file at the same time as speaking), more
packets can be sent, providing greater flexibility.
Packet switching engenders greater complexity. It also has some
potential disadvantages for speech and other time-sensitive information.
It is quite possible that when the transmitter tries to send a packet the
radio resource is temporarily full. The transmitter will need to wait until a
resource becomes free. However, if this delay is too great, a pause will
result in the speech received at the other end. For this reason, no mobile
radio systems to date have transmitted speech using packet transmission.
However, as explained in Chapter 6, packet transmission systems for
speech have been devised for the fixed network and it seems likely that
the increasing importance of the Internet will eventually result in packet
transmission over mobile radio networks.
There are two variants of packet switching: connection-oriented and
non-connection-oriented. In the case of connection-oriented, a virtual
The basics of mobile radio 79
circuit is established between the transmitter and the receiver, passing
through the switching nodes, when the first packet is received. All subse-
quent packets received for the same destination travel via the same route
with the result that they will be received in the order in which they are
transmitted. In the case of non-connection-oriented, each packet is
treated as if no previous packet had been sent. Potentially, a packet could
be sent via a different route from the previous packet and, hence, the
packets might not arrive at the receiver in the order that they were sent.
The receiver then requires a sufficient buffer so that it can correctly order
the data prior to presenting it to the user.
Recently, the data traffic on the public-switched telephone network
(PSTN) has grown to the extent that data volumes are soon expected to
exceed voice volumes. In the world of mobile radio, this trend is less pro-
nounced but can be expected to occur eventually. This has lead some to
note that modern communications systems should perhaps be packet
based rather than circuit based. In the world of fixed networks, a new
packet-switching protocol, asynchronous transfer mode (ATM) described in
Section 6.3, has been designed that can guarantee low delays for high pri-
ority traffic, thus allowing it to be used for both voice and data.
As the world changes from sending data over predominately voice
networks to sending voice over predominately data networks, the under-
lying structure of the network will need to change as well. Future radio
systems are likely to be increasingly based on packet transmission rather
than today’s circuit-switched systems.
2.6 Theoretical capacity of
mobile radio systems
The maximum capacity that can be achieved from a given piece of radio
spectrum was determined by Shannon in the early part of the twentieth
century. An understanding of this theory allows the advances that
might be achieved in mobile radio systems to be better understood. This
section looks at some of the underlying theory in order to determine
the maximum capacity that might be achieved within likely spectrum
assignments.
The maximum information that can be transmitted per second per
hertz of radio spectrum, C, is given by the Shannon law, which states that
80 The Complete Wireless Communications Professional
()
CSN=+log /
21(2.9)
where S/Nis the SNR at the receiver. However, in a tightly clustered situa-
tion, the performance of the system tends to be dominated by the signal-
to-interference ratio (SIR) rather than the SNR. Gejji [11] and Webb [7, 12]
performed some work in this area. Gejji started with Lee’s equation [13],
relating the number of radio channels to SIR, and given by
mB
BSIR
=t
C23(2.10)
where Btis the total available bandwidth, Bcis the bandwidth required per
call, and mis the number of radio channels per cell. He then replaced S/N
in Shannon’s equation with SIR and substituted for Bc(=Rb/C) within
Lee’s equation to derive
()
mBSIR
RSIR
=+
1 224 1
2
.log
αt
b(2.11)
where Rbis the user bit rate and αis a factor relating to the closeness to
which the Shannon limit can be approached.
In a well-designed GSM system, engineers typically use a SIR of
around 12 dB. For a 1-MHz spectrum assignment and a user bit rate
of 13 kbps (the rate of the GSM voice coder) (2.11) predicts a total of
96 voice calls per cell per megahertz. As shown in Chapter 3, GSM
achieves much less than this, perhaps 4.5 voice calls per cell per mega-
hertz, while cdmaOne may achieve 12 voice calls per cell per megahertz
(these numbers are discussed in more detail in Chapter 14). Hence, Shan-
non predicts that an eight-fold increase in capacity per cell is still theoreti-
cally possible. In some ways, this comparison is unfair. For example,
Shannon says nothing about the efficiency of the voice coder. If a mobile
radio system with a higher bit rate voice coder that could tolerate more
errors were deployed, a smaller cluster size would be possible and the
mobile radio system would appear to move closer to the Shannon limit.
In practice, approaching close to the Shannon limit with a mobile
radio system is very difficult because of the irregularity of natural features
resulting in the need to allow margins when designing networks and also
in the nonideal nature of Rayleigh fading requiring complex error control
The basics of mobile radio 81
systems and equalizers. Further losses occur in the inefficiencies present
in all the multiple access methods as discussed in Section 2.4.8. It is hard
to predict how much more closely mobile radio systems might be able to
approach this limit in the future, but the complete wireless professional
should be wary of systems that claim to approach close to this limit or
even go beyond the limit.
References
[1] Steele, R., ed., Mobile Radio Communications, London: John Wiley, 1992.
[2] Doble, J., Introduction to Radio Propagation for Fixed and Mobile Communications,
Norwood, MA: Artech House, 1996.
[3] Siwiak, K., Radiowave Propagation and Antennas for Personal Communications,
Norwood, AM: Artech House, 1998.
[4] Webb, W., and L. Hanzo, Modern Quadrature Amplitude Modulation, London:
John Wiley, 1994.
[5] Schwartz M, Telecommunications Networks: Protocols, Modelling and Analysis,
Reading, MA: Addison-Wesley, 1987.
[6] Redl., S. M., M. K. Weber, and M. W. Oliphant, GSM and Personal
Communications Handbook, Norwood, MA: Artech House, 1998, Ch. 11.
[7] Webb, W., “Modulation Methods for PCNs,” IEEE Communication Magazine,
Vol. 30, No. 12, Dec. 1992, pp. 90–95.
[8] Franks, L. E., “Carrier and Bit Synchronisation in Data Communications, A
Tutorial Review,” IEEE Trans. on Communications, Vol. COM-28, No. 8,
Aug. 1980, pp. 1107–1121.
[9] Glisic, S., Spread Spectrum CDMA Systems for Wireless Personal Communications,
Norwood, MA: Artech House, 1997.
[10] Prasad, R., CDMA for Wireless Personal Communications, Norwood, AM:
Artech House, 1996.
[11] Gejji, R. R., “Channel Efficiency in Digital Cellular Communications
Systems,” Proc 42nd IEEE Vehicular Tech Conf., Denver CO, 1992.
[12] Webb, W., “Spectrum Efficiency of Multilevel Modulation Schemes in
Mobile Radio Communications,” IEEE Trans. on Communications, Vol. 43,
No. 8, Aug. 1995, pp. 2344–2349.
[13] Lee, W. C. Y., “Spectrum Efficiency in Cellular,” IEEE Trans. on Vehicular
Technology, Vol. 38, No. 2, May 1989, pp. 69–75.
82 The Complete Wireless Communications Professional
Further reading
Akaiwa, Y., Introduction to Digital Mobile Communications, New York:
John Wiley, 1997.
Balston, D., and R. Macario, Cellular Radio Systems, Norwood, MA:
Artech House, 1994.
Calhoun, G., Digital Cellular Radio, Norwood, MA: Artech House, 1988.
Faruque, S., Cellular Mobile Systems Engineering, Norwood, MA: Artech House, 1996.
Freeman, R., Radio System Design for Telecommunications, New York:
John Wiley, 1987.
Meyr, H., Digital Communication Receivers: Synchronization, Channel Estimation, and
Signal Processing, New York: John Wiley, 1997.
Pahlavan, K., and A. Levesque, Wireless Information Networks, New York:
John Wiley, 1995.
Webb. W., Understanding Cellular Radio, Norwood, MA: Artech House, 1998.
The basics of mobile radio 83
Cellular radio
technologies
The essence of success is that it is never neces-
sary to think of a new idea oneself. It is far
better to wait until someone else does it, and
then copy him in every detail, except his
mistakes.
Aubrey Menen
3.1 The range of cellular
systems
Many mobile radio professionals will be
involved in the world of cellular radio, either
on the design and manufacture of hardware
or on the deployment and running of cellular
networks. This chapter looks at the different
technologies in overview. For almost all of
these technologies there are specialized books
detailing all aspects of the technology [1–5].
Here, the salient differences and key refer-
ences are introduced.
The wide range of different cellular
standards in the world today is shown in
85
Contents
3.1 The range of
cellular systems
3.2 GSM
3.3 cdmaOne
3.4 Other systems
3
CHAPTER
Table 3.1. Broadly these are divided between analog and digital systems
and between different regions of the world.
It is worth considering why there are so many different systems.
Some countries encourage the adoption of a single system on the basis
that it will bring benefits to consumers roaming throughout the country.
86 The Complete Wireless Communications Professional
Table 3.1
Cellular Systems Worldwide
Name
Analog or
Digital
Major
Countries/
Regions of Use
Date of
Introduction
Frequency
Band Key Features
NMT Analog Scandinavia,
East Europe,
South East Asia
early 1980s 450 MHz and
900 MHz
Allowed
roaming
between
countries
AMPS Analog United States
and South
America
mid 1980s 800 MHz —
TACS Analog West and South
Europe, Asia
mid 1980s 900 MHz Derived from
the AMPS
system
GSM900 Digital Worldwide 1992 900 MHz See Section 3.2
GSM1800 Digital Worldwide 1994 1,800 MHz Same as GSM
but at a higher
frequency
GSM1900 Digital United States,
Chile
1996 1,900 MHz Same as GSM
but at a higher
frequency
D-AMPS Digital United States mid 1990s 800 MHz and
1,900 MHz
—
cdmaOne
(previously
known as
IS-95)
Digital United States,
Asia-Pacific
late 1990s 800 MHz and
1,900 MHz
Only system to
use CDMA
PDC Digital Japan mid 1990s 800 MHz —
The acronyms in this table are:
TACS
NMT
AMPS
GSM900
GSM1800
GSM1900
PDC
D-AMPS
Total Access Communication System;
Nordic Mobile Telephone;
Advanced Mobile Phone Service;
Global system for mobile communications;
GSM at 1,800 MHz;
GSM at 1,900 MHz;
Personal digital cellular;
Digital AMPS.
Others allow any systems to be used on the basis that competition will
benefit the consumer. There is a certain national pride in some cases at
having a “homegrown” radio system—this is particularly true in the case
of Europe and Japan. Finally, some companies feel that they have
invented a better radio system and try to sell this system in order to make
a profit—Qualcomm is a good example of this.
When comparing the different systems, the key parameters from user
and operator points of view are the features and facilities that the systems
offer, their capacity for a given spectrum assignment, and their cost.
Broadly, all the digital systems provide more features than the analog sys-
tems and a higher capacity. Among the digital systems the features are
similar; however, as discussed in Section 14.4, CDMA-based systems
appear to have a higher capacity than TDMA-based systems. Typically,
CDMA base stations are more expensive, but fewer are required because
of the increased capacity. Calculating which system is least expensive
then becomes highly problematic.
In order to really understand the differences between the systems it is
necessary to delve into their technical parameters. These are given in
Table 3.2.
When comparing the systems it is important to understand that it is
not always the technically best systems that become the most popular.
The classic example of this is the battle of video recorder formats between
VHS and Betamax. Although Betamax was widely considered to be tech-
nically superior, VHS is now the worldwide standard because it was first
Cellular radio technologies 87
Table 3.2
Technical Parameters of the Different Systems
Name
Multiple Access
Method Voice Bandwidth
Carrier
Bandwidth
Modulation
Type
NMT FDMA 25 kHz 25 kHz analog FM
AMPS FDMA 30 kHz 30 kHz analog FM
TACS FDMA 25 kHz 25 kHz analog FM
GSM900 TDMA 25 kHz (full rate),
12.5 kHz (half rate)
200 kHz GMSK
D-AMPS TDMA 10 kHz (full rate)
5 kHz (half rate)
30 kHz DQPSK
cdmaOne CDMA 13 kHz or 8 kHz 1.23 MHz QPSK (downlink),
OQPSK (uplink)
PDC TDMA 8.33 kHz 25 kHz DQPSK
into the market and particularly because it became the format for which
the most software was available. There is a similar argument for mobile
radio. Once one system has become accepted in numerous countries, it
makes sense for other countries to adopt the same standard because this
allows their subscribers to roam, making the service more attractive. Also,
the increased sales for this standard provide economies of scale that make
the equipment less expensive than other systems. GSM has started down
this virtuous route, which often means that even if it has less capacity
than cdmaOne, it is still preferred for all these other reasons. This point is
discussed in more detail in Chapter 14. Reference works can be found on
almost all of these systems and include [1–7].
The GSM system will be described in substantially more detail than
any of the other cellular or PMR systems because most of the other sys-
tems have much in common with the design of GSM.
3.2 GSM
3.2.1 System architecture
A schematic overview of the GSM system is shown in Figure 3.1. The sys-
tem is composed of three main elements: the switching subsystem, the
base station subsystem, and the mobile. The switching part makes the
connection between two users, the base station part controls the commu-
nications across the radio interface, and the mobile acts as the transmitter
receiver for the user.
The base station subsystem (BSS) is shown in Figure 3.2. The BSS con-
sists of a collection of transmitters, known as base transceiver stations (BTSs)
and the base station controllers (BSCs). The BSCs are concentrating points to
which a number of transmitters are connected before being connected
back along a single line to the switch. This hierarchy simply serves the
function of reducing the number of connections into the switch, thus sim-
plifying the role of the switch.
The switching subsystem is shown in Figure 3.3 and consists of the
switch and a number of additional databases. In order to find where the
mobile is, there are two databases keeping track of the mobile’s location:
the HLR and the visitors’ location register (VLR). The basic concept is that
every mobile should have an entry in a database alongside which is stored
details of its last known location.
88 The Complete Wireless Communications Professional
In the GSM system, each MSC has its own VLR. When a mobile
moves into a different MSC area, the new MSC loads the information
Cellular radio technologies 89
Other
networks
GSM
The switching system
Base station system
Mobiles
Figure 3.1 Overview of the complete GSM system.
Base station system
(BSS)
BS
C
BTS
BTS
Cell
BTS
Figure 3.2 The base station subsystem.
from the mobile’s HLR into its VLR. This reduces the processing time
for calls being set up by storing all the necessary parameters locally
and prevents the more frequent interrogation into different networks
that would occur if location update messages always had to be sent back
to the HLR.
Fraud and theft are key concerns in mobile networks; hence, at regis-
tration of the mobile the switch verifies that it has not been stolen. It
does so by sending the mobile identity to the equipment identity register
(EIR), which contains details of all stolen mobiles. The authentication
center (AuC) authenticates the mobile using the procedure described in
Section 2.4.3.
All calls into and out of the mobile radio network pass through the
gateway mobile switching center (GMSC). The GMSC acts as the point of
interface between the GSM network and the PSTN. The PSTN knows that
all calls for mobiles in that network should be routed to the GMSC, and
similarly, the mobile network knows that all calls destined outside
the network should be sent to the GMSC. In the case of an incoming call,
90 The Complete Wireless Communications Professional
The switching system
(SS)
EIR
HLR
AuC
VLR
GMSC MSC
Key:
AuC - Authentication center
HLR - Home location register
VLR - Visitors' location register
MSC - Mobile switching center
GMSC - Gateway MSC
EIR - Equipment identity register
Figure 3.3 The switching subsystem.
the GMSC interrogates the HLR to determine the location of the sub-
scriber and then routes the call on to the correct MSC (which may be in a
different network if the mobile has roamed).
3.2.2 Locating a subscriber and
starting calls
A basic problem for a cellular system is finding out where the subscriber is
located and forming a channel with that subscriber. The various stages of
this process are described in the following subsections.
Locating the subscriber To locate the subscriber, the HLR keeps a
record of the MSC area in which the subscriber last registered. The VLR, of
which there is one associated with each MSC, keeps a record of the loca-
tion area in which the subscriber last registered. A location area is a group
of neighboring cells that has been “placed” in the same location area by
the operator. Each cell in a particular location area broadcasts the same
location area code so that the mobile is able to determine when it has
moved into a new location area. If location areas were not used and the
mobile had to register whenever it moved into a new cell, then the regis-
tration traffic would be very high, resulting in a waste of radio spectrum.
The mobile is also instructed to periodically send a registration message,
even if it has not moved to a new location area, to overcome the cases that
the mobile moves out of coverage and so becomes uncontactable or that
the location databases crash and need to be rebuilt.
Paging and random access An incoming call for a mobile is routed to
the GMSC of the mobile’s home network using the first digits of the
mobile number to determine the home network. The GMSC interrogates
the HLR that provides the MSC area in which the mobile last registered.
This allows the call to be switched to the current MSC (which may be in a
different network). The MSC then arranges for paging messages to be sent
to all cells in the location area where the mobile last registered. The
mobiles listen on the paging channels for a message for their number. If
they receive such a message, they instigate a random access procedure
that is essentially the same procedure as used for random access in the
case that the mobile user presses the send button.
The random access procedure is as follows. The mobile transmits a
short message on the random access channel containing only a random
number and a brief guide as to the cause of the random access. The
Cellular radio technologies 91
message is kept as short as possible to reduce the risk of collision with a
random access message sent by another user. The network responds with
a message repeating the random number and providing a dedicated chan-
nel for subsequent communications. The mobile listens for this random
number and, if it hears the number it transmitted, moves to the dedicated
channel where it can relay details of the service it requires and the
number the user wants to call. If the mobile does not hear its random
number repeated, it assumes that the message collided with the random
access message from another user and, after a random time (so that the
two users who collided are unlikely to retransmit at the same time), it
retransmits its request. Once on the dedicated channel, the network
sends back to the mobile its own telephone number to overcome the
unlikely case that two mobiles were sent a random access message at the
same time and with the same random number. If a mobile hears the
wrong telephone number, it must leave this channel and retry to send a
random access message again. Once on a dedicated channel, if the ran-
dom access was in response to paging, then the mobile indicates this as the
reason for random access and the incoming call can be connected to the
mobile.
Handover Once in a call it must be possible to hand over the mobile to
neighboring cells. To provide the necessary input information to achieve
this, the mobile is instructed to continually provide measurements of the
signal strength from surrounding cells. It makes these measurements
during the TDMA bursts when it is not transmitting or receiving. The
MSC collects these measurements along with its knowledge of the quality
of the existing link. In the case that it decides that a handover is necessary,
it tells the new cell to prepare a channel, takes note of the channel it has
prepared, sends a message to the mobile telling it the channel to which to
move, checks that the mobile appears on this channel, and then deacti-
vates the old channel. The MSC may also decide to hand over mobiles due
to traffic congestion. If there is one highly congested cell (say because of a
football match just finishing), then mobiles in the cell who could also get
coverage from other neighboring cells might be instructed to hand over to
reduce the load on the congested cell.
Call routing The routing of a call in a cellular system was discussed
briefly previously. An incoming call (say from a fixed network) is routed
to the GMSC in the home network. The GMSC interrogates the HLR to
92 The Complete Wireless Communications Professional
determine to which MSC to route the call. The problem with this
approach occurs in the case that a subscriber has roamed to a different
country—say, a French subscriber roaming to Germany. A call from a
fixed phone in Germany would be routed to the GMSC in France, where
it would be routed back to the relevant MSC in Germany. Two interna-
tional calls have been generated when a national call would have been
sufficient. New developments in the GSM standard are underway to
overcome this “trombone” problem.
3.2.3 Transmission within GSM
Having considered briefly the GSM system, this section looks in more
detail at the transmission of information from the network to the user.
Hence, it is concerned only with the part of the system between the BTS
and the mobile. For a more detailed description of the GSM system, refer
to [1–4]. GSM adopts a TDMA transmission format as discussed in
Section 2.4.8. The remainder of this section examines in more detail the
manner in which this is divided among the different users.
3.2.3.1 Framing format for speech
GSM uses a TDMA framing format. This means that each radio channel is
split into slots and each user is given one of eight slots in which to trans-
mit. The slots are numbered 0,1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, …. The radio
channel is normally referred to as a carrier. A particular allocation of one
in every eight slots is referred to as a traffic channel. So each carrier con-
tains eight traffic channels, normally numbered from 0 to 7. Each user
who makes a call needs his or her own traffic channel. Each transmission
by a user is known as a burst. For the user given all the slots numbered 1,
the first burst would be in the first slot, the second burst in the ninth slot,
and so on.
There is a requirement on the mobile to send information concerning
the received signal strength from surrounding cells back to the network in
order for the network to be able to decide when the mobile should be
handed off to surrounding cells. Transmission of sufficient signaling
information to make a sufficiently rapid handoff decision requires a data
rate of around 400 bits per second after error correction. This is approxi-
mately 1/24 of the data rate provided within GSM. Hence, after every
24 bursts of speech information, one burst of signaling information is
sent. In GSM the 26th frame is left empty, for reasons associated with the
Cellular radio technologies 93
half-rate speech coding system and channel measurements that will be
explained later. The framing structure for the full-rate speech channel is
shown in Figure 3.4, where Thas been used for traffic, which could be
speech; Sfor signaling; and the 26th burst is kept free. As can be seen, the
basic structure is 12 traffic bursts, followed by a signaling burst, another
12 traffic bursts, and a free burst. The transmission then repeats on the
26 burst cycle.
If the half-rate speech coder is employed, then only half as many
bursts are required for speech. However, the same capacity is required to
transmit measurement information because handoff decisions still need
to be taken with the same speed. Users share a slot, as shown in
Figure 3.5. Burst 26 is now used to transmit signaling information from
the second mobile.
The transmission of signaling information as shown in Figures 3.4
and 3.5 is said to take place on the slow associated control channel (SACCH).
It is called associated because it is linked with the traffic taking place on
that burst and slow because the data rate is relatively slow.
3.2.3.2 Framing format for control purposes
Similarly to the traffic information, it is necessary to send a range of con-
trol information to the mobile. Most of this information is of relevance
when the mobile is in idle mode, although some is read by the mobile
when making measurements of surrounding cells. All the control infor-
mation is multiplexed together onto a number of control channels, typi-
cally one in cells with less than four carriers and two or more in cells with
more carriers than this.
The key functions of the control channel are:
◗To help the mobile locate the control channels;
◗To provide information as to when the speech and control chan-
nels’ repetition cycle starts;
◗To provide information on parameters in the cell;
◗To provide information on surrounding cells;
◗To provide paging information;
◗To allow random access attempts from the mobile.
94 The Complete Wireless Communications Professional
Cellular radio technologies 95
Slots 12 34567812345678123456781…
Bursts for user
allocated slot 1 1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526 1
TTTTTTTTTTTTSTTTTTTTTTTTT T
Figure 3.4 The traffic channel structure for full-rate coding.
96 The Complete Wireless Communications Professional
Slots 12 34567812345678123456781…
Bursts for user A
allocated slot 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 1
TTTTTTSTTTTTT T
Bursts for user B
allocated slot 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 1
TTTTTTTTTTTTS
Figure 3.5 The traffic channel structure for half-rate coding.
Helping the mobile find the control channels When a mobile is
turned on in a new location, it does not know where the control channels
are located. First the carriers being used in the vicinity are detected by
measuring the signal strength on each carrier frequency and identifying
the strongest carriers. To help the mobile identify the control channels,
the network periodically sends a pure sine wave on these frequencies.
The mobile listens to each carrier for a period equal to the repetition rate
of this sine wave burst and, if it is detected, selects the carrier as the con-
trol carrier.
The GSM specifications state that in the next burst on the same chan-
nel after the sine wave, synchronization information containing the
current position in the framing structure must be sent. The mobile can
therefore listen to the next burst and determine at what point the control
channel is within its current cycle. The specifications also state that the
third burst of the control channel must contain the broadcast control
channel (BCCH) information, which provides a full guide to the data
contained within the complete control channel. Hence, once the mobile
has listened to a synchronization burst, it will await the third cycle of the
control channel and then decode the position of the complete contents of
the channel.
The repetition period of the control channel is 51 cycles. The number
51 has been selected because it has no common multiples with the
26 burst cycle used for the speech frames. Indeed 51 =(2 ×26) −1, a delib-
erate selection that results in the control channel repeating exactly one
burst less than twice the repetition of the speech channels. This enables
the mobile to make measurements of the signal strength in neighboring
cells, as will be explained later.
Superframes and more The framing structure has a number of levels
as shown in Figure 3.6. At the bottom of the figure is the 8-TDMA frame
and then the 26 repetition and 51 repetition cycles of the voice and con-
trol channels, respectively, as already explained. A single superframe
occurs when the speech and control channel restart at the same time.
Because 26 and 51 have no common multiples, this means that the super-
frame occurs every 26 ×51 =1,326 bursts. This is a useful point for syn-
chronization purposes because it helps a mobile switching from a control
channel to a speech channel to understand better when to transmit. A
hyperframe is comprised of 2,048 superframes and only exists because
the hyperframe number is useful as part of the ciphering process.
Cellular radio technologies 97
Contents of a burst The structure of a typical burst is shown in
Figure 3.7. At either end of the burst is the provision for the mobile to
ramp up and ramp down its power levels in order to avoid an abrupt
change in transmitted power that would generate interference over
a wide frequency range. Also included is the sounding sequence, as
explained in Section 2.4.8, which is used to determine the ISI present in
the channel in order to train the equalizer correctly.
98 The Complete Wireless Communications Professional
12345678
TDMA frame 4.6 ms
1234
26 multiframe 120 ms
23 24 25 26 1234
51 multiframe 235 ms
48 49 50 51
1234
26 51
superframe 6.1 sec
×
48 49 50 51
Hyperframe 3 hr, 28 min
123 25 26
Figure 3.6 Frame hierarchy.
Tail
3Information
58 Sounding
26
Stealing bits
1
Information
58
Tail
3
0.577 ms
Content
N of bits
0
Figure 3.7 Burst structure.
The sounding sequence is placed in the middle of the band such that
the time difference between receipt of the sounding sequence and of any
of the data bits in the burst is reduced to a minimum. As a result, the
changes in the radio channel as a result of the movement of the mobile
between the point of receiving the sounding sequence and receiving the
data will be minimized. However, the implication is that the mobile needs
to store the first half of the burst until the sounding sequence is received
and then the burst can be decoded.
The stealing bits indicate whether the information is provided for sig-
naling or user data purposes. In most cases, this information is obvious as
signaling information is provided on the signaling channels and user data
on the traffic channels. However, in some cases, such as when a rapid
handover is required, it is necessary to send signaling relating to the user
more rapidly than is possible on the SACCH and a user data frame is “sto-
len” to make way for signaling. This means that the user data is not trans-
mitted, resulting in a slight break in voice. When signaling information is
sent in this manner it is said to be sent on the fast associated control channel
(FACCH).
Making measurements of adjacent cells As already mentioned, the
mobiles need to make measurements of the received signal strength from
surrounding cells in order to provide sufficient information for the net-
work to make handoff decisions. These measurements are performed
during the TDMA slots where the mobile is not doing anything else. The
mobile receives downlink information from the base station during one
slot (say slot 0) and transmits back on the uplink three slots later (slot 3). It
also requires a slot to tune its synthesizer to a different frequency. As a
result, slots 1, 2, 4, and 7 would need to be used for retuning were the
mobile to attempt to measure a different frequency. This leaves the
mobile slots 5 and 6 to measure surrounding cells. Since it is unlikely that
the slot structure in the surrounding cell is precisely aligned with that in
the current cell (propagation delay alone will ensure that alignment is
unlikely), the best that the mobile can expect during this time is to read
one whole burst from the surrounding cell.
The specifications state that the mobile must read the control channel
of the surrounding cells to confirm that it is measuring the cell that the
network thinks that it should be. (It is possible that, due to frequency
reuse, in some parts of the cell the mobile may receive a signal from a dif-
ferent neighboring cell than that expected by the network.) To do this, the
Cellular radio technologies 99
mobile needs to extract the base station identity code (BSIC) from the control
channels. There is little chance of doing this in the free slots discussed pre-
viously because, unless the control channel happens to be on slot 5 in the
neighboring cell, the mobile’s measurement period will not coincide with
the control channel—hence, the reason for a free burst during the 26th
burst of the traffic channel. This allows the mobile to listen to all eight
slots of one cycle of the TDMA signal, during which time it will be able to
receive one burst of the control channel.
The mobile first needs to decode the frequency correction burst and
then the synchronization burst in the neighboring cell in order to deter-
mine at what point the BSIC will be transmitted. There is onlya1in10
chance that the mobile will find a frequency correction burst the first time
it listens to the neighboring control channel. Hence, it needs to keep lis-
tening on every 26th burst in order to find the frequency correction chan-
nel. This is the why control channels have a different repetition cycle
from traffic channels—whenever the 26th burst on the traffic channel
repeats there will be a different burst on the control channel to which to
listen.
With the control channels repeating every 51 cycles, a mobile making
measurements in frame 26 would actually read frames 26, 1, 27, 2, 28, 3, ...
of the control channels. Hence, an FCCH will be found within 10 repeti-
tions of the 26 slot frame and an SCH will be found 2 repetitions later.
Finding the BCCH could take up to 51 repetitions of the 26 multiframe,
although on average it will take half of this, or around 3 sec. With an aver-
age of six neighboring cells, reading all the BCCH channels will take an
average of 18 sec and a maximum of 36 sec. Clearly, if the mobile is mov-
ing rapidly through small cells, then this may be problematic.
GSM numbering scheme Each mobile has at least three, sometimes
more, dedicated phone numbers. First, the mobile has the phone number
dialed in order to reach it; this is known as the mobile station integrated serv-
ices digital network number (MSISDN). However, if this were the only
number and this number were to change, then it would be necessary to
return all the SIM cards for reprogramming. The SIM card is a smart card
containing details of the subscriber identity, some memory to enable sub-
scribers to store phone numbers, and the encryption algorithm. Having
such an easily removable identity element has allowed GSM to bene-
fit from “SIM card roaming” whereby users traveling from Europe,
where GSM operates on 900 MHz and 1,800 MHz, to the United States,
100 The Complete Wireless Communications Professional
where GSM operates on 1,900 MHz, for example, can hire a mobile in the
United States but insert their own SIM card and hence still make and
receive calls using their European number and it is not necessary to recall
SIM cards.
In addition to the MSISDN, the user is given another number that is
not visible to them and is known as the international mobile subscriber iden-
tity (IMSI). During an incoming call, the HLR performs the translation
between MSISDN and IMSI. Now if a phone number is changed, this
database can be updated.
The IMSI is stored on the SIM card. Because the IMSI can be taken out
of a phone so easily, it is no good for tracing stolen mobiles. The phone
itself also needs a serial number. This number cannot be removed from the
mobile and is known as the international mobile equipment identity (IMEI).
Spectrum efficiency The spectrum efficiency of GSM can be calcu-
lated as follows. GSM uses TDMA. Each of these TDMA carriers is 200-kHz
wide and accommodates eight ongoing calls. So in each 2 ×1 MHz of radio
spectrum there can be 1,000/200 =5 carriers, giving 5 ×8=40 ongoing
calls. At least one channel is needed for control purposes, so only 39 or
perhaps even 38 ongoing calls can be handled, but the control channel
capacity is normally neglected in calculations because it is not greatly sig-
nificant. In a typical GSM network the cluster size is 12. So in each cell, in
each 2 ×1 MHz, 40/12 =3.3 simultaneous calls can be accommodated.
This is the spectrum efficiency of GSM, 3.3 calls per 2 ×1 MHz per cell. In
the case of the half-rate coder, this rises to 6.6.
With frequency hopping it is possible to reduce the cluster size to as
little as 6. However, the carrier with the control channel on it cannot be
frequency hopped because it needs to be transmitted on a fixed frequency
to allow mobiles in neighboring cells to make measurements of signal
strength. Taking the higher cluster size for these carriers into account, the
average cluster size might be between 7 to 9, increasing the capacity by
around 30%. Capacity enhancement is discussed in more detail in
Section 9.4.
3.3 cdmaOne
cdmaOne is also known as IS-95 and a detailed description can be found
in [6]. Here, an overview of the system is provided. cdmaOne is a cellular
Cellular radio technologies 101
system based around a similar network architecture to GSM. The key dif-
ference arises in the use of CDMA as the air interface technique rather
than the TDMA used in GSM. As a result, each user transmits on the same
frequency but is given a particular code to use by which their transmis-
sions can be distinguished from those of other users. The same frequency
is also used in neighboring cells since signals from each user can be dis-
criminated from interference through the use of their code. This results in
a cluster size of 1, maximizing the reuse of the frequencies and giving
cdmaOne a higher capacity than GSM.
The downlink transmission is shown in Figure 3.8 and consists of a
number of control channels and traffic channels. The control channels
include the pilot channel, synchronization channel, and paging channels.
These correspond loosely to the frequency control channel (FCCH), synchro-
nization channel (SCH), and paging channels (PCHs) in the GSM system.
Speech is encoded using a variable rate voice coder. This generates data
between 1.2 kbps and either 9.6 kbps or 13 kbps, depending on the coder
used. The data rate depends on whether the user is speaking. Essentially,
this is a form of discontinuous transmission where the bit rate falls when
the user has nothing to say. However, by varying the rate rather than just
having an “on or off” decision, the clipping of speech is reduced and the
overall quality is higher. The variable rate results in less interference to
other users when this user is not speaking. After the speech coding, error
correction coding is applied to generate a data rate of 19.2 kbps. The same
rate is generated regardless of the voice rate by duplicating data. This is
then interleaved before being scrambled for security and inserting power
control bits into the datastream to allow the mobile to regulate its power.
The signal is next spread by the allocated 64-bit Walsh codes, resulting in
a data rate of 19.2 kbps ×64 =1.228 Mbps. Where the voice rate is
low, erasure signals are generated so that parts of the signal are not trans-
mitted, reducing interference. The use of 64 Walsh codes allows a maxi-
mum of 64 channels; but in practice, if all these channels were used,
interference from other cells would be so great that it would not be possi-
ble to correctly decode the signals. Finally, the signal is multiplied by the I
and Q channel pilot sequences. These differ for different base stations and
remove most of the interference that would otherwise occur between
neighboring base stations since all use the same Walsh code family.
cdmaOne is unique amongst current cellular radio standards in
that transmission on the uplink is different from transmission on
102 The Complete Wireless Communications Professional
the downlink. The uplink transmission is shown in Figure 3.9. The
same variable rate speech coder is used along with more powerful
error correction coding, giving a bit stream of 28.8 kbps (as opposed to the
19.2 kbps used on the downlink). This signal is then spread using the
Walsh codes. However, instead of assigning a code to each user, each six
bits of data point to one of 64 Walsh codes and this leads to a data rate of
28.8 kbps ×64/6 =307 kbps. Hence, more than one user in the same cell
could be using the same Walsh code on the uplink at the same time. To
Cellular radio technologies 103
Pilot channel (all 0s) +
W0+
+
I-channel pilot PN
sequence
Sync
channel
1.2 kbps +
W32 +
+
Convolutional
encoder and
repetition
Block
interleaver
Repeat
4 times
Paging
channel +
WP+
+
Convolutional
encoder and
repetition
Block
interleaver
Paging channel
long code mask
Long code
generator
+
Traffic
channel
Traffic
channel
+
Wi+
+
User i long
code mask
User i long
code mask
M
U
X
+
Wj+
+
Power
control
bit
Power
control
bit
+
+
Q-channel pilot
PN sequence
M
U
X
Convolutional
encoder and
repetition
Convolutional
encoder and
repetition
Block
interleaver
Block
interleaver
Long code
generator
Long code
generator
Figure 3.8 cdmaOne downlink transmission.
generate the necessary orthogonality (or near-orthogonality in this case)
each mobile generates a unique code to complete the spreading. This code
is taken from the pseudorandom code set. Each user generates the same
pseudorandom code, termed a “long code” because of its long repetition
time. However, each user uses a different offset within this code, resulting
in the required near-orthogonality. This multiplication results in a data
rate of 307 kbps ×4=1.228 Mbps, the final transmitted rate. This is finally
multiplied by the pilot I and Q channel PN sequences for that particular
base station, again to reduce interference between different base stations.
The reason for the differences between the uplink and the downlink
transmissions is due to the fact that the downlink transmission is synchro-
nous whereas the uplink transmission is not. The downlink transmission
will be synchronous because all the channels follow the same path from
the base station to the user and hence experience the same delays. How-
ever, on the uplink, the signals arrive from mobiles that are located at dif-
ferent distances from the base station and hence have different delays
associated with them. Truly orthogonal codes, such as Walsh codes, pro-
vide the greatest capacity but only under conditions of synchronization. If
they are not synchronized, they rapidly lose their orthogonality and the
capacity of the system collapses. Nearly orthogonal codes such as PN
codes do not provide such high levels of capacity as orthogonal codes, but
their capacity does not change much when not synchronized—hence, the
greater reliance on Walsh codes for all the spreading on the downlink but
only part of the spreading on the uplink. The loss of capacity as a result of
104 The Complete Wireless Communications Professional
Data bits
9.6 kbps
4.8 kbps
2.4 kbps
or
1.2 kbps
Convolutional
encoder rate
1/3 and
repetition
Block
interleaver
Walsh code
64-ary
modulator
Long code mask Long code
generator
+
+
+
I-channel pilot PN
sequence
Q-channel pilot PN
sequence
I
Q
28.8
kbps
28.8
kbps 307.2
kbps
1.2288 MHz
1.2288
MHz
Figure 3.9 cdmaOne uplink transmission.
the use of lesser codes means that typically the capacity of cdmaOne is
limited by the uplink capacity.
cdmaOne capacity is best determined by examination of practical sys-
tems rather than analysis. In practice, systems have been able to obtain
around 15 mobiles per carrier for mobile systems and up to 30 “mobiles”
per carrier for fixed (WLL) systems. With 15 calls per 1.2288 MHz, the
capacity per cell per megahertz is given by approximately 12 voice calls
per cell per megahertz, which is substantially better than the capacity that
GSM is able to provide.
Soft handoff In GSM, when a handoff decision is made, the mobile
disconnects from one cell and then reconnects with another cell. Momen-
tarily it is out of contact with the network and during this time there is a
danger that a call may be dropped. cdmaOne overcomes this problem by
allowing a mobile to be in contact with more than one base station at the
same time. This is possible because the CDMA transmissions in each cell
are on the same frequency, and hence mobiles are able to receive trans-
missions from a number of cells at the same time using a single RF front-
end. Normally, the transmissions from other cells are not destined for the
mobile and, hence, form interference that is removed during the CDMA
decoding process. However, if the network determines that the mobile is
approaching a boundary between two cells, it can instruct the new cell to
send the same signal to the mobile as the old cell. The transmissions use
different codes, so the mobile requires two (or more) baseband receiver
units to decode the simultaneous transmission. It can then discard which-
ever transmission is weakest.
As it moves between the two base stations it will gradually change
from discarding most of the frames from the new base station to discard-
ing most of those from the old base station. Eventually, the network
decides to stop transmission from the old base station to the mobile. The
soft handoff process tends to result in better signal quality during the
handoff process with a reduced chance of call dropping.
The disadvantage of such an approach is that two (or more) channels
are used by a single mobile during handoff, reducing the overall system
capacity by as much as 40% depending on the degree of overlap between
cells (and hence the number of mobiles in soft handoff at any particular
time). Calculations have shown that the increase in voice quality out-
weighs the loss in capacity, and soft handover is a mandatory part of the
cdmaOne system.
Cellular radio technologies 105
3.4 Other systems
There are two other major digital cellular systems in the world today.
These are the IS-136 standard in the United States, often known simply as
TDMA, and the personal digital cellular (PDC) standard in Japan. IS-136
was designed to increase the capacity of the analog AMPS system by
allowing an increased number of voice channels in the 30-kHz bandwidth
of a single AMPS channel. To do this it uses TDMA in 30-kHz channels,
providing three timeslots. Using quadrature modulation this provides a
sufficient bit rate per user. IS-136 features a much simpler logical channel
structure than GSM, has field structures within the timeslots that fulfill
four logical tasks, and removes most of GSM’s complex framing struc-
tures. The modulation adopted is π/4DQPSK. The PDC system is similar to
the IS-136 system but lacks the complex interworking functions with a
legacy analog protocol.
References
[1] Mouly, M., and M.-B. Pautet, The GSM System for Global Mobile
Communications, Paris, published by the author, 1992.
[2] Tisal, J., GSM Cellular Radio, New York: John Wiley, 1997.
[3] Redl, S., M. Weber, and M. Oliphant, Introduction to GSM, Norwood, MA:
Artech House, 1995.
[4] Redl, S., M. Weber, and M. Oliphant, GSM and Personal Communications
Handbook, Norwood, MA: Artech House, 1998.
[5] Harte, L., IS-136 and IS-54 TDMA Technology, Economics and Services, Norwood,
MA: Artech House, 1998.
[6] Glisic, S., and B. Vucetic, Spread Spectrum CDMA Systems for Wireless
Communications, Norwood, MA: Artech House, 1997.
[7] Padgett, J., C. Gunther, and T. Hattori, “Overview of Wireless Personal
Communications,” IEEE Communications Magazine, Jan. 1995, pp. 28–41.
106 The Complete Wireless Communications Professional
Private mobile radio
systems
If I’d known I was going to live so long, I’d
have taken better care of myself.
Leon Eldred
4.1 Introduction
There is a wide range of users who own their
own radio systems. These systems are typi-
cally known as PMR, although in the United
States they are also known under the name
SMR and by some in the United Kingdom
under the acronym PBR. Strictly, the term
SMR applies only to the shared usage of a sys-
tem; that definition will be used throughout
this chapter. The complete wireless profes-
sional should know something about this
market and these technologies because:
◗Some mobile radio engineers will end up
working in this area;
107
Contents
4.1 Introduction
4.2 Simple private
radio systems
4.3 TETRA
4.4 Other systems
4
CHAPTER
◗As will be seen, many PMR users are migrating to cellular, influenc-
ing the design and usage of cellular radio systems;
◗Some of the design principles employed in PMR technologies and
networks are instructive for the designers of other networks.
In the early 1980s, a new type of shared PMR system was introduced
called SMR in the United States and public access mobile radio (PAMR)
within Europe. With an SMR system, the network is owned and operated
by an SMR operator such as Nextel, in just the same manner as a cellular
network is owned and operated by a cellular operator. However, the mar-
ket base for an SMR operator is typically PMR users who wish to transfer
to a shared system. Of course, these users could transfer to a cellular sys-
tem (and many do); the difference between SMR and cellular is that SMR
networks are intended to be more aligned with the needs of PMR users.
They typically allow group calls, have no interconnect to the PSTN, and
charge users a fixed monthly fee regardless of usage. For heavy PMR
users, these systems are often more cost effective than cellular. Life for
SMR operators in most countries is getting increasingly difficult as cellular
operators target their market and reduce their prices. However, in certain
situations, particularly in the United States, SMR operators are experi-
encing growth, often as a result of their roaming capabilities rather than
their group and broadcast calls.
The marketplace The PMR marketplace is varied, comprising a
wide range of users. The total PMR and PAMR market in Europe in
1996 (the last year for which figures were available but these numbers
only change slowly) comprised some 4.5M mobile radio terminals. By
comparison, the U.S. marketplace over the last few years is shown in
Figure 4.1.
The figure shows a market that has been growing steadily at around
8% per year, with SMR taking an increasing share of the market. In 1996,
the growth in SMR was around 10% while in PMR it was only around
2.2%. This growth in SMR in the United States is predicted to continue, as
shown in Figure 4.2.
The predictions about the U.S. SMR marketplace show an amazing
annual growth of 32% with all the growth coming from digital SMR serv-
ices. This is completely unlike any other country with SMR (or PAMR)
operations where subscriber numbers are, at best, rather static.
108 The Complete Wireless Communications Professional
The breakdown of the total number of PMR users within the major
European countries is shown in Table 4.1. In some countries the data
were not available to segment the user population; hence, only the total is
provided. Similar information was not available for the United States, but
it is likely that the percentage of users in each category will be similar
between the United States and Europe.
The data reveal a sizable European market of over 4M terminals.
However, compared to the cellular marketplace, the PMR and PAMR
market is perhaps only one tenth of the size. In total, the PMR market is
Private mobile radio systems 109
0
2
4
6
8
10
12
14
16
18
Installed units (millions)
Year
SMR
PMR
1986 1988 1990 1992 1994 1996
Figure 4.1 The PMR and SMR market in the United States (Source:
The Strategis Group, London).
0
2
4
6
8
10
1997 1998 1999
Year
2000 2001 2002
Digital SMR
Analog SMR
Installed untis (millions)
Figure 4.2 Predictions of the SMR marketplace in the United States
(Source: The Strategis Group, London).
110 The Complete Wireless Communications Professional
Table 4.1
European PMR and PAMR Market
Country Transport Utility Industry Government Public Safety Services Other Total
Austria 34,000 10,000 26,000 21,000 45,000 — 36,000 1,173,000
France 113,700 52,000 110,000 110,000 135,000 65,000 66,000 1,675,000
Germany ———— — ——1,230,000
Italy ———— — ——1,400,000
Spain 33,000 14,000 47,000 47,000 12,000 51,000 7,800 1,211,000
Sweden ———— — ——1,215,000
Switzerland 19,000 9,800 45,000 20,000 47,000 7,0300 3,600 1,144,000
United
Kingdom
180,000 41,000 90,000 97,000 95,000 70,000 277,000 1,850,000
Total* 4,440,000*
*Also includes data from Denmark, Finland, Hungary, Iceland, Lithuania, Norway, Portugal, Romania, and Turkey.
expected to grow by 3% a year.1This is around the level of GDP growth of
most countries and suggests that PMR growth is, at best, linked with eco-
nomic growth.
The total PMR market can be segmented into 10 distinct groups. This
segmentation allows the needs and economics of each group to be consid-
ered separately. Statistics for each group in the United Kingdom are pro-
vided in Table 4.2; the breakdown is similar for the other major countries.
In this table, the estimated average cost per terminal per annum to the
user includes both capital and revenue components associated with both
terminals and infrastructure. For users operating significant control
rooms they do not include the costs associated with control room
equipment.
The general market segment can be subdivided and summarized as in
Table 4.3.
The figures show a total market value of approximately $450M. The
public safety organizations provide some 20% of this market, with the
rest being divided among a number of smaller user communities.
The choice between cellular, SMR, and PMR Until the 1980s, the
only viable form of mobile communications available was through
self-provision of infrastructure and mobiles. PMR is the oldest form
of land mobile radio and has grown steadily over the last thirty or
forty years.
Despite its growth, however, PMR has its problems. These include:
◗Increasing congestion of the radio spectrum that has tended to
result in a deteriorating grade of service on many systems, particu-
larly in major cities;2
◗The need for users to construct and maintain the necessary infra-
structure even though mobile communications engineering may
have little to do with the core competencies of their organizations;
Private mobile radio systems 111
1. Actually, statistics on the PMR market are rarely gathered, and there are few good
predictions available. Some recent work [1] suggests that the PMR marketplace may
actually be in a state of decline.
2. Many techniques have been adopted to combat this congestion, including moving from
voice to data transmission. These will be discussed on more detail throughout this
chapter.
112 The Complete Wireless Communications Professional
Table 4.2
Summary of Market Segments
Emergency
Services Utilities Railways
Local
Government
National
Government
General
PMR
Back to
Back CBS
Includes Police, fire,
ambulance
Gas,
electricity,
water
Rail and rail
police
(excludes
underground
railways)
County,
metropolitan,
regional, and
district
councils
Defense,
police,
immigration
Taxis,
couriers,
delivery,
security,
industry,
etc.
Mainly
on-site users
including
security, etc.
Commercial
common
base station
services
Number of
terminals
95,000 41,000 30,000 82,000 15,000 360,000 170,000 50,000
Cost/user/
year
$800–$1,100 $1,100–$1,300 $1,100–$1,300 $500–$650 $800–$1,100 $250–$1,100 $120 $300–$500
Annual
value
$96M $50M $35M $50M $16M $160M $21M $20M
◗Being locked into long system replacement cycles (typically
10 years) that inhibit the ability to ensure that mobile communica-
tions are reactive to the changing needs of the organization.
Until 10 years ago these limitations were accepted as a fact of life
because there was no real alternative. The advent of public cellular serv-
ices did provide an alternative. However, there has been only limited
migration from PMR to cellular, for a number of reasons:
◗Cellular has been traditionally viewed as much more expensive
than PMR.
◗Cellular does not offer a number of facilities that PMR offers and
that are now central to the operational practices of many users.
These include group calls, fast call set up, direct mobile to mobile
calls, and various dispatcher facilities.
◗Cellular does not offer the degree of area coverage that a small
number of users require (for example, the electricity companies
require coverage along all pylon routes).
◗Many PMR users, particularly the major users, are extremely nerv-
ous about losing direct control over the provision of their mobile
communications, fearing that if a service provider does not perform
as they would wish, there would be little they could do to improve
matters.
Private mobile radio systems 113
Table 4.3
Summary of General Segment Subdivisions
Number of
Terminals Cost/User/Year
Annual
Value
Taxis/private car hire 142,000 $250–$500 $50M
Motorcycle/ pedal cycle dispatch 10,000 $250–$500 $4M
Bus and coach operators 17,000 $250–$500 $6M
Construction companies 5,500 $250–$500 $2M
Large stores 10,000 $250–$500 $4M
Car industry 2,900 $250–$500 $1M
National 60,000 $800–$1,100 $56M
Other large users 13,000 $250–$500 $5M
Other users 100,000 $250–$500 $35M
◗PMR handsets are available in specialized forms with special indica-
tors and displays and are more rugged than typical cellular
handsets.
With the success of cellular in the early to mid-1980s, it seemed likely
that there would be a similar market for shared provision of mobile radio
communications for users who were currently operating their own PMR
system. However, the SMR market has broadly failed to live up to expec-
tations with many operators merging and recording low growth. The rea-
sons for this are varied but essentially relate to the high costs of providing
a national network for a relatively small number of users compared to cel-
lular, resulting in cellular services being both better and cheaper for many
applications. It is against this background that operators are considering
launching new digital SMR networks, an investment plan that seems dif-
ficult to justify.3
The GSM operators are looking increasingly well placed to enter the
PMR market as the GSM standard continues to evolve. In particular, work
by the International Railways to provide the PMR services of group calls
and fast call setup within the GSM standard has resulted in the GSM stan-
dard containing most of the features required by PMR users.
A key issue in the choice between cellular, SMR, and PMR is the cost.
As the tables have shown, the cost of PMR for many users is only in the
region of $400 per year compared to around $1,000 per year for the aver-
age business user on cellular. Nevertheless, a steady migration away from
PMR and toward cellular and perhaps SMR systems seems inevitable in
the coming years.
4.2 Simple private radio
systems
PMR systems were the first operational type of radio system. Al-
though PMR technology has evolved dramatically over the years, some of
the PMR systems deployed are comparatively simple. The most basic PMR
systems consist of a simple open-channel transmission system. Here, the
114 The Complete Wireless Communications Professional
3. Indeed, at the time of writing, consolidation was taking place throughout Europe with the
number of PAMR operators considering digital networks being approximately halved.
base station is typically located in the building owned by the company.
The base station and the mobiles are all tuned to the same channel, typi-
cally around 200 MHz in Europe or 450 MHz and 820 MHz in the United
States and having a bandwidth of 25 kHz or 12.5 kHz. Whenever an ana-
log voice signal is transmitted it is heard by all the mobiles, which are just
functioning as receivers. There is no discrimination between transmis-
sions intended for individual mobiles nor is there discrimination between
more than one user of the radio channel. When a mobile wants to trans-
mit back it simply sends an analog voice signal on the uplink channel. If
more than one mobile transmits at the same time, then it is likely that nei-
ther of their messages will be heard. The coverage area is limited to a sin-
gle cell and the traffic levels are limited to what can be sent down a single
channel, allowing for message collisions.
Such systems are fine for many users. For example, a taxi dispatcher
would typically find this system satisfactory. However, problems are
caused by a lack of radio spectrum. Because there are more users who
would like to operate their own PMR systems than there is spectrum to
give them, some sort of sharing needs to take place. One simple means of
sharing is to give the same channel to more than one user in the same
area. If both users only transmit small amounts of voice, then they will
rarely collide and the utilization of the channel will be enhanced. How-
ever, problems now occur in that both sets of mobiles will hear all trans-
missions, despite the fact that only some of these transmissions have been
made from their base station by their controller. This is both annoying for
the user and can lead to some confidentiality problems (in the case, e.g.,
where two taxi companies share the same piece of radio spectrum). The
next level of complexity was a way of overcoming this problem.
There are a number of ways of ensuring more privacy. One is a con-
tinuous tone-controlled signaling system (CTCSS). In CTCSS, one of up to
32 subaudio tones is transmitted throughout the duration of the call.
These tones range from 67 Hz to 250 Hz. A tone decoder in the receiver
mutes the receiver unless the correct tone is present. By giving all mobiles
from the same company the same tone but all mobiles from a different
company a different tone, users will at least not hear conversations from a
different company (however, they will still not be able to use the channel
when other users are transmitting). The receiver will prevent a user
transmitting onto the channel when there is a signal already on the chan-
nel with a different CTCSS tone, which the user will be unable to hear.
Private mobile radio systems 115
A variation on CTCSS, more widely used in the United States, is digi-
tally controlled squelch (DCS).4Here, a 23-bit sequence is transmitted con-
tinuously at a subaudible bit rate. Because demodulation of this signal is
moderately difficult without synchronization information, the number of
sequences is restricted to 104 different codes. The receiver listens for a
particular code and only lifts the mute in the receiver if this code is
present.
One of these two techniques is generally used on shared channels to
differentiate between users. The users can take this sharing a stage further
by noting that since only one base station can transmit at any one time,
they might as well share the same base station and reduce costs. Such an
approach is known as common base station (CBS). The CBS is typically
owned by a third party and leased to all the different user groups. At the
CBS is equipment that ensures only one user can access the channel at
any particular point in time. Although seemingly sensible, CBSs have not
been particularly successful for a range of commercial reasons and a lack
of radio spectrum.
In the case where there are not sufficient CTCSS or DCS tones to dis-
tinguish between the different users, which might be the case where it is
required to address individual users rather than teams of users, selective
calling (SELCALL) can be used. In SELCALL, five sequential tones are sent
at the start of each transmission. Each tone is drawn from 1 of 10 codes,
allowing up to 10,000 users to be identified. The receiver will only lift the
mute if the tone sequence detected is the same as the sequence with
which it has been programmed. Group calling is also possible using a
wildcard character so that 1234G would call mobiles in the range 12340
to 12349. Because SELCALL takes place at the start of a call, a mobile
coming into the coverage area part way through the call would not be
able to detect who the call was for and so would not be able to join the call.
In principle, such systems can only work in a single cell since there is
no mechanism for changing to a different frequency when moving into a
neighboring cell. However, some users have found means to work
around this using quasi-synchronous transmission. In this arrangement,
116 The Complete Wireless Communications Professional
4. The “squelch” control in a simple radio is a knob that is turned to set the level at which
the speaker is turned on. This means that the user does not have to hear hiss when there
is no transmission on the channel but that they will hear voice when it is broadcast,
assuming that the noise is below the “squelch level” and the voice above it. Controlled
squelch allows the mobile to set the “level” on behalf of the user.
the same signal is sent from neighboring cells on the same frequency. If
this is not arranged very carefully, then the effect for a user on the bound-
ary between two cells is to receive a two copies of the same signal with a
delay between them. This is akin to receiving ISI and can result in the sig-
nal being unintelligible (especially in analog systems where it is not possi-
ble to deploy equalizers). The only way to make such an arrangement
successful is to ensure that the signals are transmitted from the different
base stations at exactly the same time and that even the modulating
waveforms are in cycle with each other at the different base stations. This
accurate timing can be very difficult to achieve when the signals all origi-
nate in the dispatcher office, are sent by landlines to the base stations, and
are then transmitted. If the landlines are of different lengths (which will
almost certainly be the case), then the signals will arrive at different times
at the base stations. It is then necessary to employ delay mechanisms and
very precise timing sources to ensure that the signals are all transmitted at
the same time. Even once this is done, there tend to be areas where the
signal cannot be well received and the system often needs fine adjust-
ments. It has been said that quasi-synchronous operation is more of a
black art than a science. However, with the advent of more advanced
radio systems, the need for quasi-synchronous operation is gradually
disappearing.
Such systems can also only work on one radio channel. Where the
capacity of the systems needs to be larger than that which can be offered
with a single channel, more complex systems must be employed. These
are generally known as trunked PMR systems due to the fact that a
number of radio channels are grouped, or trunked, together. As discussed
in Section 2.3, Erlang theory shows that trunking a number of radio
channels together actually provides much more efficient use of the radio
spectrum than the case where each user only has access to one channel.
As soon as the need to work on more than one channel is introduced, the
complexity of the mobile radio system rises very quickly toward the com-
plexity of a cellular system. Indeed, the distinction between cellular and
PMR systems starts to become unclear when PMR systems include
trunking.
The most widely used trunked PMR system in the world is MPT1327.
This unhelpful name comes from the U.K. telecommunications stan-
dard number 1327 that governs its behavior. Because the presence
of a standard facilitated competition, MPT1327 rapidly overtook
Private mobile radio systems 117
proprietary trunking systems such as Motorola’s Smartnet and Smart-
zone or Ericsson’s EDACS as the preferred option for users. The basic
design of an MPT1327 standard calls for a number of 12.5-kHz channels
in each cell. One of these channels is nominated as the control channel
and provides paging messages for users, telling them of the presence of an
incoming call and the channel on which this call will be provided. Most of
the principles are the same as for GSM but somewhat simplified.
MPT1327 is often known as an analog PMR system because voice calls are
carried in an analog form on 12.5-kHz dedicated channels. However, the
control channel carries digital information, encoded on the analog chan-
nel using fast frequency shift keying (FFSK)5at a data rate of 1.2 kbps. To find
a control channel, the mobile searches each of the known channels for
the presence of FFSK signaling and, when it is found, decodes synchro-
nizing messages on the channel for confirmation that it is a valid control
channel.
The control channel is divided into 106.7-ms-wide slots in which
128 bits can be transmitted. This is split into two 64-bit codewords:
◗The control channel system codeword (CCSC), which contains a 15-bit
code that identifies the relevant mobile or group of mobiles and
synchronization information to ensure that the mobiles know
when the slots start and stop;
◗The address codeword that contains the signaling message; if longer
than 64 bits, the next CCSC can be replaced by another address
message up to a maximum of four address messages.
When the mobiles transmit on the control channel they send a syn-
chronization code and an address codeword followed by their message.
There are a number of different message types:
◗Aloha messages control the random access messages sent by the
mobiles.
◗Requests are sent by the mobiles to request a call.
◗Ahoy messages demand a response from the radio to ascertain its
location.
118 The Complete Wireless Communications Professional
5. FSK is part of the frequency modulation family. FFSK refers to the use of rapid transitions
between different symbols using a particular optimal pulse-filtering technique.
◗Acknowledgments are sent to ensure handshaking of messages.
◗Go to channel messages send the mobile to the appropriate traffic
channel.
◗Single address messages are used in special cases where it is necessary
to send the radio serial number.
◗Short data messages allow the transmission of short bursts of data up
to 184 bits long between users.
◗Other includes, for example, network information.
More information about the MPT1327 standard can be found in the
MPT1327 specification, [2] or [3].
4.3 TETRA
4.3.1 Introduction
TETRA is intended to be one of the new generation of digital PMR
equipment that also includes APCO25 as the equivalent U.S. standard.
Standardization has taken place during the 1990s within ETSI, and in
1998 the first TETRA product was starting to appear. TETRA is designed to
be a multipurpose mobile radio system for a wide range of users including
emergency services, utilities, airports, and PAMR operators. Although
possible technically, it is thought unlikely that TETRA systems would be
deployed by small users such as taxi companies since this option would be
expensive. However, such users might become subscribers to a shared
TETRA system. The TETRA standard is complex and extremely compre-
hensive. A fully specified TETRA radio will be more advanced than a GSM
handset and able to perform a wider range of functions.
TETRA comes in two basic forms: the TETRA voice and data system
(TETRA V+D), which is designed for general purpose use and provides
voice and data circuit-switched connections, and the TETRA packet data
optimized (TETRA PDO) standard, which is designed for packet data appli-
cations. Both standards operate over the same physical TETRA network
but are designed to be optimized for different tasks. In order to describe
TETRA in more detail this section will concentrate on the V+D standard.
Private mobile radio systems 119
This also includes a direct mode capability whereby one terminal can talk
directly to another without the need for infrastructure.
In order to fully understand the capabilities and design of a TETRA
network, it is important to know that much of the standardization work
was driven by the police forces throughout Europe. As a result, TETRA has
a range of facilities designed primarily for public safety applications. Some
have questioned whether this very high level of specification has left
TETRA over-specified for commercial applications. This remains to be seen.
An overview of a TETRA network is shown in Figure 4.3. As can be
seen, much of the architecture is similar to that of GSM, although there is
the additional mobile to mobile mode shown at the bottom of the figure
that is not available within GSM. Given that TETRA has many of the func-
tions of a cellular network, this similarity should not be surprising.
4.3.2 System operation
The operation of the TETRA system is similar to the operation of GSM. On
power-up, the radio searches for a control channel and registers itself
120 The Complete Wireless Communications Professional
Mobile
switching
center
Location
register
Base
transceiver
station
Network
management
Operations and
maintenance
Subscriber
management
Gateways to
other networks
PSTN, ISDN, PDN, etc.
Inter-system
interface to
other
TETRA
networks
Mobile
station
Direct mode
communication
Mobile
switching
center
Location
register
Mobile
station
Figure 4.3 Overview of a TETRA network.
onto the network. The coverage area is divided into a number of location
areas, the mobile station only being paged in those cells in its current loca-
tion area. Mobiles need to reregister upon moving into a new location
area. Unlike GSM, TETRA does not have a handoff procedure. Instead it
makes use of a fast call reestablishment procedure such that when it
moves to another cell, the call can be rapidly reestablished in the new cell.
The break in communications can be made to be virtually as short as for a
handoff in GSM.
TETRA has a very high level of security, commensurate with its
deployment in emergency services. It allows both air interface encryp-
tion and end-to-end encryption of information. The actual encryption
process, including the use of a temporary identity, is very similar to that
used in GSM where a random number is sent to the user that they com-
bine with their secret number and return the result; however, the GSM
system cannot provide end-to-end encryption.
The random access process at the start of a call is also similar to GSM.
The base station sends information as to when random access is allowed
that is monitored by the mobile. The base station can allow different
access classes of mobile access at different times. There are four access
classes, A to D, and the mobiles are assigned one of these four access
classes in a manner that can be defined by the operator. The access classes
can also be linked with message priorities so that at any point the lower
priority messages can be blocked. Once a particular access class is allowed,
a mobile picks a random number of slots after the first allowed access and
makes an access attempt using a slotted-Aloha protocol. A successful
access is acknowledged with an ACCESS-ASSIGN message from the base
station that contains details of the reserved channel that the mobile
should use for further communications. Unlike GSM, the initial random
access contains a substantial amount of information. Although this
increases the probability of random access collisions, it means that for a
successful message the call setup time can be reduced because less signal-
ing is required at the start of the call. Rapid call setup has been judged to
be essential for public safety use. After the ACCESS-ASSIGN message, the
mobile is given a short transmission resource to allow it to linearize its
power amplifier by transmitting a short burst. It can then move directly to
transmitting voice frames.
Once in a call, TETRA offers a range of handoff mechanisms. There
are five types of cell reselection depending on:
Private mobile radio systems 121
◗Whether a call is currently in progress and if so whether it is a group
call or individual call and whether the mobile concerned is the
transmit mobile or the receive mobile (i.e., listening to a group call);
◗Whether the mobile had sufficient time to gain information on the
new cell;
◗The grade of call reestablishment supported by the infrastructure.
The categories of call reestablishment are:
◗Undeclared, where the mobile is not currently in a call and simply
makes an idle mode reselection decision;
◗Unannounced, where the mobile is currently engaged in a circuit
mode call but does not have the opportunity to inform the infra-
structure that it is changing cell; in this case, it must make a random
access in the new cell and detail its situation, and the break in com-
munications could last for more than 1 sec;
◗Announced type 3, the same as unannounced;6
◗Announced type 2, where a mobile engaged in a circuit mode call
informs the present cell of its intention to find service on a new cell
and then negotiates directly with the new cell on its main control
channel (MCCH);
◗Announced type 1, where a mobile engaged in a circuit mode call
informs the current cell of its intention to find service on a new cell
and of its preferred cell; negotiations for access to the new cell are
performed via the present serving cell, channel allocations on the
new cell are issued by the present serving cell, and this process
amounts to seamless handover.
In order to provide the greatest flexibility, the TETRA specification
offers a number of modes of service. Some of the key modes follow.
Normal mode The normal mode is intended to cope with the major-
ity of installations where there are typically four or five carriers in use
on each site. Here, the first timeslot on the main carrier is set aside to
122 The Complete Wireless Communications Professional
6. It is not clear why there are two seemingly identical categories. This is probably a historic
“accident” of standardization.
form the control channel. All mobiles not in a call listen to this control
channel. The base station transmits on all downlink slots of the main car-
rier in order to allow mobiles in neighboring cells to measure signal
strength.
Extended mode In larger installations, more than one control chan-
nel may be required. A common secondary control channel with the
same functionality as the main control channel is transmitted but is only
used by a subset of the users.
Minimum mode The minimum mode is used in low-traffic density
areas where there is typically only a single carrier deployed. In this mode,
all the timeslots on the main carrier can be set aside for traffic. Hence, only
the control channel frame, frame 18, is available for control channel pur-
poses. Mobiles must be aware of when the base station has entered mini-
mum mode and not attempt to decode traffic information.
Time sharing mode In the time sharing mode, a carrier is shared
between a number of base stations by only being used for some of the
time. This is only suitable for very low traffic density areas.
4.3.3 Technical parameters
TETRA operates in a TDMA frequency division duplex mode. Each carrier
is 25-kHz wide and provides 4-TDMA frames. The signal is modulated
using π/4 differential quadrature PSK (D-QPSK) modulation7that allows
the encoding of 2 bits/Hz. After allowing for guard bands, this results in an
overall transmission rate of 36 kbps per carrier or 9 kbps per user. How-
ever, it is possible to assign more than one slot to one particular user,
allowing them to increase their data rate to 32 kbps. Transmission and
reception slots are staggered by 2 time slots so that mobiles do not need to
transmit and receive at the same time. Further, uplink and downlink slots
need not be paired but can be assigned to different users. The basic TETRA
framing structure is shown in Figure 4.4.
Private mobile radio systems 123
7. QPSK transmits 2 bits per symbol using a constellation of four points of equal amplitude.
D-QPSK uses the difference between transmitted symbols rather than the absolute value
to encode the information. π/4 D-QPSK changes the constellation by 45 degrees each
symbol period, resulting in a continually changing waveform that helps clock recovery at
the receiver.
Unlike GSM, there are no additional control channel structures to
complicate the framing structure. The control channel forms the 18th
frame of every multiframe, allowing control messages to be sent along
with the voice call information. This is called the SACCH and is equivalent
to the SACCH in GSM. The normal burst structure involves a short period
for ramping up in power, the first half of the user data, the training
sequence, and the second half of the user data. After allowing for the error
correction information, the user can send up to 408 bits per time slot,
allowing a maximum data rate of 7.2 kbps. One frequency pair per site is
designated to carry the MCCH. Normally slot 1 on this channel is used for
control purposes.
TETRA offers a number of area coverage techniques.
◗Single-site wide area coverage: This is a straightforward single base sta-
tion on a high site providing good coverage but poor spectrum effi-
ciency as a result of the large cell size.
124 The Complete Wireless Communications Professional
1234
1 time slot 510 modulating bit periods 14.167 ms==
123 4
1 TDMA frame 4 timeslots 56.67 ms==
1 multiframe 18 TDMA frames 1.02 sec==
509 510
123 4
1 hyperframe 60 multiframes 61.2 sec==
17 18
123 4 59 60
Figure 4.4 The TETRA framing structure.
◗Cellular channel reuse: Normally used in a medium- to high-traffic
density networks, a cellular-type deployment is adopted with a
clustered arrangement of frequencies as introduced in Section 2.3.
◗Quasi-synchronous transmission: Used in areas that cannot be covered
by one site and where a limited number of radio channels are avail-
able, special synchronization techniques are necessary for the base
station and the technique by which the control center is connected
to each of the base stations. A special class of mobile may also be
required with a complex equalizer.
◗Time sharing transmission: This is the same as the time sharing mode
discussed previously where a carrier is only deployed in a given cell
for some of the time and is rotated around a number of cells.
As can be seen, with the introduction of TETRA, the differences
between cellular systems and PMR systems have become very small
indeed. The implications of this will be discussed further in Section 14.2.
4.4 Other systems
There are two other key digital systems under development. One is the
APCO25 system being developed in the United States for public safety
purposes, which uses FDMA but otherwise provides very similar func-
tionality to TETRA. The other is Motorola’s iDEN, which is a proprietary
system used by Nextel to provide PAMR service across the United States.
Because of their similarity to TETRA, they are not described further here.
References
[1] MPT1327, MPT1327 Specification. Available from the Radiocommunications
Agency; see www.open.gov.uk/radiocom/rahome.
[2] Holbeche, R. J., ed., Land Mobile Radio Systems, London: Peter Peregrinus,
1985.
[3] NERA, Smith, Review and Update of 1995 Economic Impact Study,
available from the U.K. Radiocommunications Agency, 1997; see
www.open.gov.uk/radiocom/rahome.
Private mobile radio systems 125
Other mobile radio
systems
I find that a great part of the information I
have was acquired by looking up something
and finding something else on the way.
Franklin P. Adams
5.1 Introduction
Although cellular and PMR make up the two
types of mobile radio system that the com-
plete wireless professional needs to under-
stand, there are a number of other types of
mobile radio system of which the communi-
cations professional should also be aware.
These include cordless systems, WLL systems,
video distribution systems such as the local
multipoint distribution system (LMDS), and sat-
ellite systems, and are introduced in this
chapter.
The key issues discussed in this chapter
are as follow.
◗Cordless phones are designed for indoor
and office applications and do not transfer
127
Contents
5.1 Introduction
5.2 Cordless systems
5.3 Wireless local
loop systems
5.4 Satellite systems
for telephony
5.5 TV, radio, and
other systems
5
CHAPTER
well to outdoor, cellular-type systems. They are typically much sim-
pler than cellular phones using lower power transmission and
higher bit-rate speech coders.
◗WLL systems are designed for fixed communications in situations
where it is easier, cheaper, or more advantageous than wireline
connections and are often based on cellular or cordless technolo-
gies. There is a wide range of different environments into which
WLL can be deployed and hence the need for a range of different
technologies. WLL systems need better voice quality and a wider
bandwidth than cellular and cordless systems.
◗Video distribution services provide an alternative TV distribution
mechanism to satellite or terrestrial broadcast but typically need
to work at high frequency bands above 20 GHz in order to
find sufficient spectrum and normally only provide one-way
communications.
◗Satellite systems are the only way to provide global coverage. In
order to provide acceptable quality, low Earth orbits (LEOs) are
required but result in the need for numerous satellites and hence
expensive systems. Whether there is a sufficient market for such a
system remains to be seen.
5.2 Cordless systems
5.2.1 Overview of cordless telephony
Considerable confusion exists about cordless telephones because they
have been used in a wide range of different roles. To understand cordless
properly, it is necessary to look at each of the different roles. We discuss
three roles here, but its role as a WLL technology in more detail in
Section 5.3.
Mobile use within the home The initial application of cordless
phones was as an extension to the fixed line in a home. The cordless base
station is plugged into the home phone socket and provides a radio link to
the handset. For such a deployment to be successful the phone needs to
be inexpensive and able to operate autonomously. The cost is kept down
by simple design and by a restriction in range to around 200m while
128 The Complete Wireless Communications Professional
autonomous operation is provided by the base station performing
dynamic channel allocation whereby it seeks the radio channel with the
lowest interference and uses that for its operation.
Mobile use within the office An obvious extension to using cord-
less phones as a way of providing mobility in the home is to do the same
thing in the office. Most offices have a private branch exchange (PBX) that
connects wires from each user’s fixed telephone. The cordless system
removes these wires, replacing them with a single connection to the cord-
less office system. This then connects to a number of base stations around
the office. To some extent this is like a minicellular system within the
office; however, the system is typically much simpler, with automatic fre-
quency allocation, typically little in the way of location updating for a
user, and a much shorter range. Nevertheless, handovers and other cellu-
lar features are provided and the user gains the benefit of mobility within
the office. To take a cordless home phone design and translate it to a cord-
less office design requires the addition of handover, the ability to control a
number of base stations, and the capability to dial internal extensions that
can be routed through the PBX. However, the basic parameters of the sys-
tem remain unchanged.
As a limited mobility cellular system The terminology here might
appear slightly strange since cellular systems have limited mobility, typi-
cally not providing coverage across all parts of the country. However,
“limited mobility” has come to be used to describe a system offering less
mobility than cellular systems. The use of cordless phones to provide a
pseudocellular system is often known as telepoint. Telepoint is the
deployment of cordless base stations in streets and public areas to provide
a low-cost service that, at first, appears similar to cellular. The key differ-
ence is that the base station range is so low that coverage can only be pro-
vided in high density areas, unlike cellular where more ubiquitous
coverage is provided. In early systems there was also the disadvantage
that incoming calls could not be received. Given that this reduction in
range is a major disadvantage, it should not be surprising that telepoint
systems have broadly failed. The United Kingdom launched four net-
works that failed, as did networks in France, Germany, and a variety of
other countries. Typically, the lack of coverage compared to cellular
makes the service unattractive. Telepoint has been successful in a very
limited number of places, namely Singapore, Hong Kong, and more
recently Tokyo. These are all very high density cities where the populace
rarely leaves the city areas. In such cities, widespread deployment of
Other mobile radio systems 129
cordless base stations can be worthwhile because of the high user density
and relatively good coverage that can be provided. The high capacity that
results from using very small cells allows many more users onto the net-
work than is possible for a traditional cellular system,1allowing call
charges to be lower than cellular, making the service an attractive propo-
sition. It is unlikely that there are many other cities in the world where
cordless will be successful in a telepoint application and its main sales will
remain as home and office phones.
The key cordless technologies of DECT and personal handiphone system
(PHS, the Japanese cordless standard) are now described in more detail.
5.2.2 Digital enhanced cordless
telephone
5.2.2.1 Introduction
The DECT specification was developed by ETSI to provide an air interface
for cordless telephony that is able to support a wide range of services.
DECT standardization began in 1988 and was still ongoing in 1998, as
new modes, such as WLL, were added into the DECT standard. DECT is
now able to support residential cordless applications, business cordless
applications, radio local area networks (LANs), and WLL systems. In order
to support this wide range of applications, DECT was designed with the
following basic features:
◗A very high voice call capacity of up to 10,000 Erlangs/km2per floor
in indoor environments with a speech quality similar to wired net-
works;2
◗High data rates with several megabits per second overall network
capacity;
◗High-capacity base stations but allowing the use of simple radios;
130 The Complete Wireless Communications Professional
1. Although not with cellular systems that deploy microcells—these can provide greater
capacity than cordless systems.
2. Although DECT can accurately claim to be able to support such high-traffic densities, this
is not primarily achieved by a highly spectrum-efficient radio system but by the capability
to install a large number of cells in proximity. Indeed, on a typical measure of spectrum
efficiency such as channels/MHz, DECT performs poorly compared to cellular
technologies.
◗A system design that is capable of avoiding the need for frequency
planning;
◗Support of ISDN services.
The DECT system can be represented by a layered model conforming
to the OSI seven-layer model. In such a representation, the lowest layer is
the physical layer. Above this sits the medium access control, and above
that the data link control. The highest level in the DECT specifications is
the network layer, conforming to the OSI layer four. Each of these layers
is discussed in the following subsections.
5.2.2.2 Physical layer
DECT divides its spectrum allocation of 1,880 MHz to 1,900 MHz into
10 discrete frequency bands, each 2-MHz wide. Each of these frequencies
is then accessed using TDMA. A diagram of the TDMA structure used by
DECT is shown in Figure 5.1.
This figure shows that the TDMA frame of 10 ms is divided into
24 slots, of which nominally 12 are used for the base station to mobile
direction and 12 for the mobile to base station direction. However, it is
possible to reverse the use of some of these slots in a dynamic fashion if
Other mobile radio systems 131
0123 11 12 13 14 20 21 22 23
Base station transmits Mobile transmits
10 ms frame period
SDZ
32 388 4
368.1 µs or 424 bit periods
Figure 5.1 The framing structure used within DECT.
the traffic to be carried is asymmetric. Each burst contains three fields.
The S-field contains synchronization information in the form of a Gold
code that aligns the timing and ensures that mobiles are aware of the cur-
rent position within the burst structure. The D-field contains the user
data, while the Z-field just repeats the last four bits of the D-field. This
allows early detection of a collision that may occur where more than one
DECT system is trying to share the spectrum in the same area.
Data is modulated using two-level FSK with a BT product of 0.5 and a
modulating data rate of 1,152 kbps. This scheme permits the use of a sim-
ple receiver with noncoherent detection and without the need for an
equalizer.
5.2.2.3 Medium access control
The medium access control (MAC) layer has three functions:
1. To allocate and release physical resources according to the
requests of the upper layers;
2. To multiplex the signaling and user information channels onto
the physical timeslots;
3. To ensure secure transmission through the use of error correc-
tion coding.
Allocation of the physical resources One of the key features of
DECT is the use of dynamic channel allocation (DCA) whereby any base
station can select any of the 10 radio channels to use at a particular
instance and with no control from the switch. This is essential in cordless
systems where users may own both the base station and the mobile and
hence no single body has control of all the base stations using the same
frequencies. Channels are selected based on the measured interference
levels, with the base station choosing the channel with the lowest
observed interference at any point in time. Regardless of whether there
are any users, each base station must always transmit on one carrier,
known as the beacon frequency. This allows mobiles to scan for the chan-
nel from the closest base station and to lock onto this channel. The chan-
nel is then used for paging messages. The beacon frequency is also used
for any ongoing calls, so it is not necessary to reserve a frequency solely
for beacon transmissions. Its function is very similar to the BCCH channel
in the GSM system.
132 The Complete Wireless Communications Professional
Multiplexing of the logical channels There are a number of differ-
ent channels in the DECT system, as shown in Table 5.1.
Many of these channels are analogous to those in GSM; for example,
the I channels are equivalent to GSM TCHs, the C channels are equivalent
to the SACCH and the FACCH, the P to the PCH, and the Q to the BCCH.
A standard MAC packet uses the 388 bits available in the TDMA burst
in the manner shown in Table 5.2.
It can be seen from this table that the paging information can be sent
as part of a frame destined for a particular user. Because this paging infor-
mation can be sent to any mobile, in a divergence from GSM, a burst can
have a dual purpose and so mobiles need to listen to all downlink bursts,
regardless of whether the remainder of the frame is destined for them.
Since each frame repeats every 10 ms, the M, N, P, Q, and C channels have
a data rate of 4.8 kbps, while the user data is transported at 32 kbps.
Other mobile radio systems 133
Table 5.1
The Different Channels in the DECT System
Name of Channel Description
I Information: This can be carrier in either a nonprotected or a
protected mode.
C Control channel for signaling, which can be slow signaling sent
concurrently with the data or fast signaling sent by stealing data
frames
M MAC internal control channels
N Identity channels
P Paging channels
Q System information broadcast channels
Table 5.2
The Usage of the 388 Bits Within the Burst
Number of Bits Usage
48 Used for either the M, N, P, Q, or C channels
16 Error correction bits (termed CRC)
320 User information or fast control channel signaling
4 Error control bits (termed X)
Error control If C, P, or Q transmissions are sent, they are protected
with a 16-bit cyclic redundancy code (CRC), a form of block coding. How-
ever, the coding is only used to detect errors, not to correct them. If P or Q
transmissions are detected to be in error they are ignored; however, if C
channels are in error they will be requested to be retransmitted. The 4 X
bits are used to detect errors in the user information. They are far too few
bits to provide any strong error protection but can indicate whether there
has been large scale interference with the burst.
5.2.2.4 The data link control and network layer
The data link control (DLC) provides higher levels of error correction for
the user data and ensures that handover is performed correctly. The net-
work (NWK) layer handles the routing of incoming calls by tracking the
location of the users in a similar manner to the GSM location registers.
More information about the DECT system can be found in [1, 2].
5.2.3 Personal handiphone system
PHS is a cordless standard developed initially for use in Japan, but which
has also found application in a number of other Asia-Pacific countries.
The standard was developed by the Japanese standardization body in
conjunction with Japanese industry.
Radio system PHS uses π/4 shifted QPSK with a roll-off factor of 0.5.
This provides similar simplicity as for DECT and equally means that
equalizers are not required. Like DECT, the multiple access method is
TDMA but using only four timeslots per carrier. TDD is also used. Carriers
are spaced at 300 kHz apart and provide a bit rate of 384 kbps. By the time
allowance is made for additional information, and for the TDD duplex,
resulting in a one-way data rate of only half of the total rate, each user is
left with a 32-kbps data rate allowing ADPCM speech coding. Antenna
diversity is employed at the base station, and by selecting the best
antenna during the base station receive mode and retransmitting on
this antenna during the base station transmit mode, diversity gains can be
achieved in both directions.
The frequency band assigned in Japan is 1,895 MHz to 1,918 MHz, of
which 11 MHz is allowed for both public (i.e., telepoint) and private
(i.e., residential cordless) use, while the remaining 12 MHz is set aside for
purely public use. In total, 77 channels are available, of which 6 are set
134 The Complete Wireless Communications Professional
aside for control channel purposes. Handover capabilities are provided. A
form of dynamic channel allocation is used, although different tech-
niques need to be adopted for control channels compared to traffic
channels. For the control channels a form of quasi-static autonomous
assignment algorithm is used, whereas for the traffic channels a standard
DCA is adopted.
Radio channel types There is a similar set of radio channel types as in
DECT and GSM. Control channels (CCHs) include the associated control
channel, common control channel, and broadcast channel that provide
system information. PCHs provide paging information while specific cell
channels (SCCHs) provide information related to call setup. User packet
channels (UPCHs) provide packet data transmission, and traffic channels
(TCHs) carry the user information.
More details about PHS can be found in [1].
5.3 Wireless local loop
systems
5.3.1 Introduction to wireless
local loop
WLL is the provision of a cellular-like phone without mobility. This may
seem a strange concept given that one of the key benefits of a cellular
phone is mobility. To understand why a mobile phone would be provided
without mobility it is necessary to separate the two cases of developing
and developed countries.
In developing countries, very few people have a telephone. In African
countries, less than 2% of the population has access to a phone. This low
level of penetration is typically because the users cannot afford to have a
phone installed in their house. Much of the cost of installation of a stan-
dard phone is associated with the cost of installing the copper cable
required to link the home to the switch—a process that has taken
100 years in developed countries. Wireless systems offer an opportunity
to provide a phone connection more quickly and at lower cost. By
restricting the position of the receiver to being mounted near an appropri-
ate window in the house, the range of the cell can be extended since there
Other mobile radio systems 135
is less blocking between the phone and the base station than would be the
case with a mobile phone. This allows fewer base stations to be used and
hence the system to be deployed more cheaply than would be the case
with a mobile system. There is also no need for the added complexity of
handover.
In developed countries the situation is quite different, with most
homes having phones. However, some countries are interested in offer-
ing a phone service in competition to the PTO and see wireless as the least
expensive means of providing the service. In these countries the user
could afford cellular systems; however, there are a number of other prob-
lems with cellular when compared to landline:
◗The voice quality is typically inferior.
◗The data rates provided are typically lower.
◗The call costs are typically more expensive.
An operator wishing to deploy a wireless service has to make use of a
technology that overcomes these problems. The first is overcome using a
higher voice coding rate, and the second using technologies providing
higher data rates. Overcoming the third is broadly achieved by only pro-
viding coverage in city areas and hence requiring many fewer base sta-
tions than would be required for a cellular system.
In principle, then, a WLL system is one employing a cellular-like tech-
nology but where the subscriber unit is fixed, providing an equivalent of a
wireline telephone, replacing the “local loop” segment between the
exchange and the subscriber’s home with a wireless link.
In recent years, some of the WLL systems being deployed have pro-
vided a combination of both fixed and mobile services and it is worth
examining in more detail why this should be the case. In principle, the
operator of a cellular network could provide a WLL service as well by sim-
ply providing users fixed versions of their mobile phones. This seems
somewhat pointless since they could equally be supplied with mobile
phones, allowing them to gain the benefit of mobility. However, the user
will only accept a replacement home phone if their call costs are as low as
a wireline phone whereas cellular calls are typically more expensive. To
overcome this, the mobile operator needs to use WLL as a means of pro-
viding the user with a lower tariff. Again, this seems pointless since the
cost to the mobile radio operator of carrying the call is the same regardless
136 The Complete Wireless Communications Professional
of whether the call comes from a fixed or a mobile phone. What is actually
happening here is that the mobile radio operator could carry all the calls
from mobile and fixed phones at the wireline rate but to do so would dra-
matically reduce their profit. By maintaining a high price for mobile calls
and a lower price for fixed calls they retain high margins on the mobile
calls while increasing the overall traffic volumes on their network.
So in summary, WLL is the use of radio technology to provide a fixed
connection to the home. There are many different technologies that can
be used, and these are discussed in the remainder of this section. Before
looking at the different wireless technologies, the different access tech-
nologies including copper, cable, and fiber optic are considered so that the
overall access marketplace can be better understood.
5.3.2 Access technologies: radio
and cable
The cellular systems discussed in previous chapters have no competition
from other modes of information delivery—if communications on the
move is required, then cellular systems have to be used. This is not the
case with WLL, despite the fact that WLL systems are based on cellular
principles. There are numerous other means of making connections from
the home to the PSTN and this set of connections is generically called the
access network. Although there are a number of different WLL technolo-
gies, which compete with each other, many perceive that the key compe-
tition to WLL comes from copper cable. Hence, it is important to
understand a little about the world of access technologies for fixed appli-
cations even though they are clearly not wireless. This section provides a
brief overview of the available technologies.
The number of access technologies is continually increasing and
includes copper cable, cable TV systems, cellular, cordless, satellite, and
even information sent over power cables as has been recently suggested.
Driving the increase in the number of access technologies is the concept of
convergence. Although meaning different things to different people,
broadly convergence predicts that a range of different media, including
voice, computer data, and video, will be transmitted along the same path,
possibly in an integrated form. What is now happening is that the delivery
channels used by each of these three applications are being expanded so
that they can become the preferred channel for converged data. This has
Other mobile radio systems 137
resulted in competition between channels that previously had little in
common—for example, between the copper laid by the PTOs and the
coax used for cable television. The complexity of the situation has been
exacerbated by liberalization of telecommunications and by tariffs that do
not reflect costs—for example, international calls cost little more to
deliver than local calls but are charged at a much higher rate.
The main contending access networks are shown in Figure 5.2. This is
a figure full of acronyms and buzz words that will be explained in the
remainder of this section. The figure itself is confusing and full, which
well reflects the confusing situation currently facing providers of access
networks. The figure shows approximately as many access networks
moving from left to right (i.e., from voice toward computing and televi-
sion) as are moving in the opposite direction.
Each of these access mechanisms is now described. At the end of each
description a brief prediction is made about the role that the mechanism
will play in the future of telecommunications.
The copper infrastructure The copper infrastructure, comprising
twisted-pair copper cables installed and owned by the state
telephone company (the PTO), has formed the traditional access
infrastructure for almost 100 years. Until recently it was ill-suited to
138 The Complete Wireless Communications Professional
Voice Computer Television
PTO High speed
Internet VoD
XDSL?
WLL Broadband WLL?
Cable TV
Cable modem
Cable
telephony
Digital TV
Broadcast
Internet
PTO/WLL
Return
channel
MVDS
Return channel
Mobile
Mobile
computing Videophone?
UMTS
Teledesic
satellite
Fixed/mobile
integration
Internet
telephony
Competition
on this plane
Figure 5.2 Different access technologies and convergence.
anything other than voice due to its low bandwidth (only around 3 kHz).
However, a number of recent advances have started to change this. Voice-
band modems can now achieve rates of up to 56 kbps, which provide slow
but viable computer access. ISDN provides rates of up to 128 kbps, offer-
ing the potential of video, albeit of a low quality. The role that this copper
will play in the future, though, will be dominated by the success or failure
of digital subscriber line (DSL) technology, which promises a massive
increase in the data rate passed through copper wire.
A whole host of different approaches to DSL systems have been pro-
posed with names such as asynchronous digital subscriber line (ADSL), high-
speed digital subscriber line (HDSL), very high-speed digital subscriber line
(VDSL), and doubtless more to come. The acronym xDSL refers to all these
approaches.
ADSL is a complicated means of getting much higher data rates down
telephone lines—being a wire-based technology, it falls outside the scope
of this book. Such a high-speed technology would allow the national tele-
communications company to deliver services such as video on demand
through existing connections. ADSL is currently under development, and
it is still not clear whether it will be successful.
Internet telephony Internet telephony is currently an application
that is concerning many existing operators. The concept is to use
advanced speech coders to compress and segment the voice and then send
the packets over the Internet. The advent of this technology is mostly arti-
ficial due to the fact that all Internet calls are charged at local rates despite
the fact that many result in international flows of data. This, in fact,
reflects the true cost of telephony provision, where the local loop section
represents the vast majority of the cost, and the national and inter-
national trunk contribution is almost insignificant. However, fixed
operators persist in inflating international prices in order to increase
profitability and in some cases subsidize the local loop. If Internet tele-
phony works (and it is unlikely to for long, even if it does work at first, as
the network simply becomes swamped by voice as well as the current
heavy data load), the net result will simply be that fixed operators will
rebalance their tariffs so that Internet telephony is no longer worthwhile.
The only advantage then will be the ability to link voice with exploring a
site so that a user could contact the operator of the site they are surfing for
help if required.
In the longer term, packet-based systems may gradually replace
circuit-switched systems, which will improve the efficiency of use of the
Other mobile radio systems 139
access networks but not necessarily change the role of any network.
Finally, it should be remembered that all Internet telephony calls take
place over existing access networks, typically the copper infrastructure.
All that changes is who gets paid and how much.
Wireless local loop WLL provides a similar level of service to wireline
systems at similar or lower data rates. However, it brings a number of key
advantages.
◗It is typically less expensive to install wireless than wireline systems.
◗Installation is more rapid.
◗Installation can be delayed until the moment when the subscriber
requires service.
◗The economics of WLL remain similar even in low-density areas,
whereas the cost per subscriber for wireline systems increases as the
distance between the subscribers increases.
As a result, WLL is being considered as an alternative to deploying
wireline systems in many countries; and some analysts have predicted
that, by the year 2005, there will be more wireless lines than wired lines
being installed. More details about WLL can be found in [3].
Cable TV Cable TV systems use buried coaxial cables to provide a
broadband service to their customers. These systems were initially one-
way TV distribution systems that provided around 50 TV channels using
analog modulation. At the receiver end, all that was required was to
change the frequency of the signal on the cable to one that was within the
bandwidth of the TV receiver. Subsequently, cable operators decided to
increase their revenue by offering telephony. This caused major problems
for many of the older networks because one-way amplifiers were in use,
which meant that the signal could not be easily carried back from the sub-
scriber. Some of these operators even added a second, telephony net-
work, using separate twisted pairs alongside their coaxial network.
Newer cable networks have overcome these problems by deploying two-
way amplifiers and carrying voice traffic over a low-frequency carrier
within the coaxial cable. Once this form of connectivity is in place, the
transmission of computer information is relatively straightforward, mak-
ing use of a modem. Because of the high bandwidth provided by a coaxial
cable, bandwidths of 30 Mbps per user can be supported, making cable
140 The Complete Wireless Communications Professional
one of the most versatile and converged networks. However, cable suffers
from a high build cost due to the cost of digging up the road and will typi-
cally only be deployed in urban areas where the user density is high.
Digital TV The advent of digital television will allow the delivery of
broadcast data in relatively large volumes. This could speed Internet
access to some of the most popular pages and provide information such as
newspapers online. Digital TV systems could offer shopping malls where
the contents of the shops are regularly broadcast and stored locally. The
key deficiency with TV is the lack of a return channel, but for applications
such as home shopping only a low-capacity channel is required, which
might be supplied by the copper of the PTOs or a WLL operator. The key
advantage of TV is the familiarity that people have with TV and teletext-
type services.
Video distribution systems Video distribution systems are broadly
the equivalent of WLL versus copper telephony but in the world of
cable systems. They attempt to provide a similar service to cable TV distri-
bution systems but using radio. There are three key types of video
distribution systems: the microwave video distribution system (MVDS), the
microwave multipoint distribution system (MMDS), and the LMDS. Just
like cable, these systems started as analog TV distribution systems, with
the first offering being the MMDS system operating at around 2 GHz and
providing around 20 TV channels. However, as time progressed, these
systems also started looking for a return path to allow telephony and
possibly computer data transmission. As with cable, the provision of a
return path is not simple, and it is the digital variants, LMDS operating at
28 GHz in the United States and MVDS operating at 40 MHz in Europe,
that will be the first to provide a return channel. However, at these high
frequencies, subscriber equipment is relatively expensive, propagation is
restricted, and hence it is not clear how cost effective the provision of such
services will be.
LMDS provided some interest in the United States in 1998 when fre-
quencies were auctioned across the country in the 28-GHz band. How-
ever, the money raised by the government was only around a quarter of
that expected and many of the licenses have gone to startup companies
where it is not clear that all will be able to find the capital required to
deploy the system. Some will deploy a one-way video distribution sys-
tem, whereas others will put in place a two-way broadband data system.
The latter will compete directly with broadband WLL systems operating at
Other mobile radio systems 141
lower frequency bands; this issue is discussed in more detail in the follow-
ing sections.
Cellular and cordless radio Cellular and cordless systems have
already been discussed in Chapters 3 to 5. As access technologies for
delivering fixed service, they have a number of shortcomings, including
relatively poor voice quality (although this is improving all the time and is
expected to be as good as wireline by 1999), lower availability, higher
cost, and lower data rates. Against this is the benefit of mobility when
within the house, using a single number that will reach the user wherever
he or she is.
A number of operators have attempted to attack the fixed line market
using cellular but generally find that they are unable to compete on price
with the fixed operator. Recently, a number of interesting initiatives have
been announced that may start to change this. The home base station
concept within GSM allows a miniature base station to be connected to
the phone socket, providing GSM coverage within the house. The wire-
less office concept deploys picocells within an office to provide excellent
coverage and capacity coupled with mobility and a single number. If these
sorts of initiatives can be provided in a cost-effective manner, then cellu-
lar systems may start to have more impact on the access market. Their key
strength is that they integrate fixed and mobile communications into one
terminal; this is discussed in more detail in Chapter 6.
Satellite systems This is the most speculative of all channels. Tele-
desic proposed a satellite network allowing high-speed access from any-
where in the world. However, a few calculations show that this network
could only handle a very small percentage of the world’s traffic and will
make no significant impact on other access networks.
Table 5.3 provides a summary of the key access technologies.
It is clear that WLL has a range of competitors, some that are less
expensive and others that can provide higher data rates. The attraction of
WLL when compared to these competitors is discussed in the following
section.
5.3.3 WLL and cellular: the
differences
Put simply, WLL networks are simplified cellular networks. They use the
same basic architecture and the same principles of radio transmission.
142 The Complete Wireless Communications Professional
However, since the subscribers do not move, they do not need location
registers, means of handing over subscribers to different cells, means of
allowing subscribers to roam to different networks, and strong means for
combating fraud, for example.
WLL networks do have to provide a better quality of voice than cellu-
lar networks since they are designed to replace wired networks. They
need to support data transmission at the rates that can be achieved
through wired networks, they need to be extremely reliable, and they
need to offer communications for a lower cost than mobile radio. These
requirements result in different design decisions between cellular and
WLL in terms of the way the radio channels are divided and the type of
antennas used, for example.
Other mobile radio systems 143
Table 5.3
Comparison of the Different Access Technologies
Access
Technology Data Rates Cost Market Share
Ordinary telephone
lines
<56 kbps Low where already
installed, high
where not installed
Around 60 to 80% in
developed
countries
ADSL Up to around
<6 Mbps to the
user, <1 Mbps to
the network
Probably less than
$1,000 where a
copper line is
already available
None at present, but
may gradually gain
a small share
Cable lines Up to 30 Mbps As with ordinary
telephone lines
Varies, but typically
20 to 90% in
developed
countries
Mobile radio <10 kbps Moderate, higher
than maintaining
existing cables,
lower than installing
new ones
Rapidly gaining
share, typically over
10% in developed
countries
Telephony WLL Typically <128 kbps,
although
broadband WLL
systems are offering
around 2 Mbps
Similar to mobile
radio, may be
slightly lower
Very little to date,
but predictions that
this could be more
than 20% by 2005
Video distribution
systems such as
LMDS or MVDS
Mbps to the user,
kbps to the network
Higher than WLL,
but true cost not
really known yet
Virtually none to
date, future impact
unclear
5.3.4 Technologies for WLL and
LMDS/MVDS
The ideal WLL product The ideal WLL product depends somewhat
upon the environment in which it is to be deployed. For emerging
countries, the ideal system would provide generally reliable voice of
understandable quality at a very low price. Products based on modified
analog cellular systems provide these facilities, but whether the price is
low enough depends on the GDP of the country. However, in developed
countries the requirements are much more stringent. To be worth
deploying a WLL system must provide:
◗Voice quality equal to the fixed network;
◗Data rates of at least 32 kbps and preferably 64 kbps;
◗Fax and voiceband modem support;
◗A second telephone line.
However, the ideal system would go well beyond this to provide:
◗Data rates equal to corporate LANs, that is, around 10 Mbps;
◗Packet data facilities to allow efficient use of bandwidth;
◗Bandwidth on demand and multiple lines to allow simultaneous
data, Internet, voice, and video transmission.
Of course, all of these facilities should be provided at a cost lower than
the revenue that can be received from the users.
Constraints on WLL systems Technically, achieving all these
requirements is relatively straightforward. Radio systems with sufficient
bandwidth and processing power are perfectly possible using standard
technology. The problems come when they are deployed. For a design
that is technically perfect, an assignment of radio spectrum at least
10 times the bandwidth offered to a user is required for the system to be
economically viable. This means that the 10-Mbps system suggested pre-
viously would need a spectrum assignment of 100 Mbps before it could be
viable, and therein lies the problem. Assignments of this size are typically
only available above frequencies of 10 GHz. However, at these frequen-
cies there can be problems with rain fading; a short communica-
tions range; and because there are no standard frequency bands,
144 The Complete Wireless Communications Professional
manufacturers are currently unable to achieve economies of scale. In an
effort to reach a compromise between cost and capacity, manufacturers
have developed a wide range of systems with varying bandwidths and
costs, offering operators a choice between an expensive but near-ideal
system or a less expensive but less ideal system.
The current range of WLL products There is a bewildering range
of WLL products, as shown in Table 5.4, with little standardization
between them. In this section some of the key systems are considered,
more details can be found in [3]. WLL technologies are generally divided
into those based on cordless standards, those based on cellular standards,
and those custom designed for WLL. The custom category can be further
divided into narrowband and broadband, with the dividing line perhaps
at around 1 Mbps per user.
The progress and strengths of each of these technologies is assessed
briefly in Table 5.5, noting that the products are changing rapidly and
hence, the strengths and weaknesses may change, and that this overview
must inevitably be somewhat superficial.
The narrowband custom technologies such as Nortel and Tadiran are
now relatively well established. Both the Nortel system and the Tadiran
system have been deployed in a number of commercial WLL networks,
such as Ionica in the United Kingdom and networks in Colombia, while
the DSC and Lucent systems have been widely trailed and were now
entering commercial deployment during 1998. Equipment prices for
most of these custom systems are still typically quite high, with subscriber
units often costing nearly $1,000 each. There seems no reason why these
prices should not fall dramatically in the next few years.
At the time of writing (1998), the broadband systems such as those
from Ericsson, Floware, and Telescicom were still mostly in the test and
development stage. Although there were several ongoing trials, it did not
appear that any of these systems had yet entered large-scale commercial
deployment. Much was unclear about these systems and the services that
they offer. Propagation characteristics at the frequencies at which they
operate are less well known than lower frequencies, the realistic system
capacity under load was not clear, deployment rules were yet to be estab-
lished, and the protocols and services to be offered were not standardized.
It seems likely that trials and early deployments might take some time
with these innovative new systems and that the technology will not be
fully mature for a number of years to come.
Other mobile radio systems 145
An intriguing possibility is the use of wireless LANs as the basis for a
WLL technology. Wireless LANs are designed to connect computers into
office networks over a range of a few tens of meters but are relatively
mature and inexpensive. By placing a directional antenna on the sub-
scriber device and increasing the transmitter power, the technologies
could be deployed for WLL systems with a range of many kilometers.
Most systems will require some modifications to compensate for the
increased signal delay and increased delay spread. Perhaps the greatest
146 The Complete Wireless Communications Professional
Table 5.4
Comparison of Different WLL Technologies
Technology
Voice
Quality
Frequency
Band
Maximum
Data Rate
Multiple
Lines
Cordless
DECT Good 2 GHz 552 kbps Up to 12
PHS Good 2 GHz 32 kbps In future
CT-2 Good 900 MHz 32 kbps No
Cellular
TACS Poor 900 MHz No No
GSM Medium 1–2 GHz 9.6 kbps No
cdmaOne Medium 1–2 GHz 9.6 kbps No
Custom
Nortel Good 3 GHz 64 kbps Yes
Tadiran Good 2–3 GHz 32 kbps Yes
DSC Good 2–3 GHz 144 kbps Yes
Lucent Good 3 GHz 128 kbps Yes
Broadband
Ericsson
AirLine
Good 10–28 GHz 2 Mbps Yes
Floware Good 3–10 GHz 4 Mbps Yes
Telescicom N/A 2–5 GHz 4 Mbps Yes
Wireless
LANs
N/A 2–10 GHz Mbps N/A
LMDS/ MVDS Not
known
28–40 GHz 10 Mbps to
home, 10 kbps
to network
No
concern is that these systems will be relatively inefficient of spectrum and
will be difficult to deploy in a cellular configuration where interference
from neighboring cells might be experienced.
The final category of systems is the video distribution technologies.
These are generally not classified as WLL systems since their primary role
is video broadcasting rather than point-to-point communications. How-
ever, their architecture is nearly identical to WLL systems, and recently
they have been acquiring return channels to enable two-way communi-
cations. These systems are known by a number of names—the early sys-
tems deployed mainly in the United States were termed MMDS and
worked at 2 GHz, the digital replacement in the United States is known as
LMDS and works at 28 GHz, while the European version is known as
MVDS and works at 40 GHz. At present LMDS and MVDS deployments
are mostly still at the trial phase. The video distribution systems are typi-
cally highly asymmetric with large downlink bandwidths of the order of
hundreds of megabits per second in order to provide tens of video
Other mobile radio systems 147
Table 5.5
Strengths and Limitations of the Key WLL Technologies
Product Strengths Limitations
DECT Standardized product with a
relatively high data rate
Small spectrum assignment
makes deployment difficult
PHS and CT-2 Standardized product Relatively low data rate and
limited spectrum
TACS Standardized and
inexpensive
Lack of spectrum, low voice
quality, very low data rate
GSM and cdmaOne Standardized and
inexpensive
Lack of spectrum, moderate
voice quality, very low data
rate
Nortel and Tadiran Mature and available Relatively low data rate of
around 32 kbps
DSC and Lucent Higher data rate of around
128 kbps, ISDN compatible
Not yet widely deployed
Ericsson AirLine, Floware,
Telescicom and others
Very high data rates of
2 Mbps
Generally not yet
commercially ready, operates
in higher frequency bands
Wireless LANs Available and relatively
inexpensive, high data rates
Not proven in a WLL
deployment
LMDS/ MVDS Provides video distribution
as well as telephony
Highly asymmetric and in a
very high frequency band
channels. Where return paths are provided, they tend to be limited to tens
of kilobits per second and are generally intended to allow video on
demand films to be selected and provide limited interaction.
Comparing reality with the ideal The ideal WLL system could be
realized by a technology based around packet transmission with a maxi-
mum bandwidth per user of 10 Mbps operating in a spectrum assignment
of 100 Mbps. Some of the new broadband technologies start to approach
this ideal in terms of data rates although few use packet data. However, at
present, they all fall short of the ideal because they need to be deployed at
high frequencies (in order to achieve a sufficient spectrum assignment),
because they are still somewhat immature, and because there is little
standardization of product, suggesting that the terminals might be expen-
sive and difficult to multisource. Although the maturity will improve
with time, it is difficult to see any change in the other areas.
Likely progress of WLL technologies The wide range of rapidly
changing WLL products leads to a number of questions such as:
◗Will the existing narrowband custom-designed technology rapidly
be outdated by the emerging broadband technologies?
◗Will broadband WLL systems be based on custom-designed
approaches or on wireless LANs?
◗Will the video distribution systems develop to the extent that they
become the preferred WLL technology, offering both broadband
data services and video distribution?
◗Will any standard for WLL systems emerge in the coming years to
stabilize the market?
The answers to these questions are far from clear. However, it seems
likely that the higher frequency of operation of the broadband systems
will demand a price premium both in equipment cost and in a higher
number of cells for some time to come. As a result, there will be a number
of niches in the market, as shown in Table 5.6.
The (relatively) narrowband systems are already being deployed by
operators wishing to compete with the PTO. These systems offer broadly
equivalent services to the fixed line but at a lower price and will become
increasingly ubiquitous as the equipment costs fall and the technology
becomes more mature. The broadband systems will be aimed at home
148 The Complete Wireless Communications Professional
teleworkers and small- and medium-sized enterprises (SMEs) who require
interconnection to LANs, intersite communications, or simply a cost-
effective alternative provision of a number of voice circuits. The combina-
tion of a difficulty in gaining radio spectrum and the current immaturity
of the broadband products means that such systems will probably start to
be deployed during 1998 and 1999, but will not become commonplace
until the year 2000 or later.
It is probably of little relevance (except for the manufacturers)
whether the broadband systems are based on wireless LANs or custom-
designed technologies. At present, most are custom-designed, but some
wireless LAN-based products will probably emerge in direct competition
during 1999.
Whether the video distribution systems will enter this market is diffi-
cult to predict. At the moment, the increased cost of operating at very
high frequencies coupled with a design aimed mainly at video distribu-
tion suggests that these systems will serve yet another marketplace—that
of video distribution. But as the broadband WLL products rise in frequen-
cies toward those used by the video distribution systems, they will start to
share components and may increasingly tend to be variants on the same
platform.
5.4 Satellite systems for
telephony
5.4.1 Introduction
For some time, cartoon characters such as Dick Tracy had wristwatch
communicators that magically beamed their signals to satellites overhead
Other mobile radio systems 149
Table 5.6
Possible Market Segments for WLL Technologies
System Data Rates Cost Role
Modified cellular <10 kbps Low Emerging countries
Narrowband
custom
<500 kbps Medium Consumer market in developed
countries
Broadband <2 Mbps Probably high,
to be seen
Home workers and SMEs in
developed countries
so that the characters could stay in communication wherever they were.
This seemed like a different world from today’s mobile phones. For users
within Europe, using GSM, the situation is not too bad, with relatively
good coverage across Western Europe and simple roaming arrangements
between different countries. However, for people in the United States,
the situation is quite different. Coverage is patchy and often only exists in
cities. Different standards and different companies operate across the
country with the result that roaming from state to state is often impossible
or at best very expensive. The U.S. standards are not widely used outside
the United States, with the result that when U.S. citizens leave the
country they can no longer use their cellular phones. Perhaps it is not
surprising that the impetus for a global satellite system providing world-
wide communications came from the United States.
The basic idea is simple. In order to cover large areas, large cells are
required. Large cells need transmitters sited high up. The best position is
somewhere in the sky, hence the use of satellites to provide coverage over
wide areas. The implementation is much more difficult. Just launching
the satellites is a high-cost and high-risk undertaking. Then there is a
requirement for a global spectrum assignment, something that is rarely
achieved. Finally, there is the standards minefield to negotiate. In this sec-
tion the concept and progress of global satellite systems is briefly exam-
ined. More complete information can be found in [4].
5.4.2 Concept
The concept of a satellite system is relatively straightforward—the system
is broadly similar to a cellular system, but with the base stations placed in
space rather than located on the ground. Satellite systems are not new,
and satellites have been used for fixed communications for over thirty
years. These types of satellite systems typically used large satellites placed
in geostationary orbits above strategic parts of the world, often across
major oceans. Large Earth stations with dishes some 30m across, placed
on either side of the ocean, communicate with the satellite. International
fixed calls are routed by the PSTN to these Earth stations in order to pass
over the satellite link to their destination. Because of the size of these
dishes, such a use of satellites is clearly not appropriate for personal
communications.
150 The Complete Wireless Communications Professional
In the 1980s, a limited form of mobile communications via satellite
became possible using the Inmarsat series of satellites. These too were
geostationary; however, advances in satellite technology enabled rela-
tively small dishes only a meter or so across to be used. Such small dishes
are known as very small aperture terminals (VSATs). This allows shipping
vessels to send signals via satellite and eventually for travelers to remote
areas to take a briefcase, with an unfolding antenna, that could be aligned
with the satellite to provide a voice link, or a low-speed data link.
News reports from remote regions are typically still sent back using this
approach.
VSATs represent the smallest and most efficient satellite terminals
deployed up until 1998. However, they are a long way from the Dick
Tracy ideal, or indeed from anything that a typical U.S. citizen would like
to carry around with them, let alone with the need to orient the antenna.
The reason why VSAT terminals have not become smaller is broadly due
to the distance that the satellite is from the Earth. To be in a geostationary
orbit, the satellite needs to be 36,000 km above the Earth’s surface. This
requires substantial transmit power and receive sensitivity and can typi-
cally only be achieved via the use of a directional antenna. It is the size
and deployment of the antenna that makes VSATs inappropriate as a con-
sumer product. VSATs also suffer from noticeable speech delay of around
one-fourth of a second due to the time it takes radio waves to travel to the
satellite and back; and finally, VSAT systems typically comprise less than
10 satellites, each with limited capacity.
The obvious solution to this problem is to bring the satellites closer to
the Earth by placing them in low Earth orbits (LEOs) between 500 km and
1,000 km above the Earth. The shorter propagation distance reduces the
delay and the power consumption to levels at which handheld terminals
without highly directional antennas can easily transmit and receive sig-
nals. These lower orbits also have smaller cell sizes, and hence the total
system capacity can be higher. A LEO system requires about 60 to 70 sat-
ellites for global coverage.
The concept of bringing the satellites closer to the Earth is not one that
requires inspired thinking; the reasons why low orbits have not been con-
sidered before are because the satellites are not stationary in space. In a
LEO, a satellite can pass overhead in less than six minutes. This requires
more complex tracking of the satellites at the Earth stations and means
Other mobile radio systems 151
that handover is required between different satellites. In practice, this
handover is simpler than in a cellular network where the network has to
deduce to which cell the mobile should be handed over. In the satellite
system, the system knows which is the next satellite coming along to
cover that area, so it knows exactly where the calls need to be handed.
Another problem with low orbits is that the satellites do not stay in
orbit for very long. They are expected to have a lifetime of only around
5 years. In order to keep a system of 70 satellites in space, that implies that
14 satellites per year will need to be launched just to replace those that
are falling out of the sky.
The means whereby the call is routed to its destination, once it
reaches the satellite, is worth further investigation. Some of the proposed
satellite systems use “switching in space,” whereas others use a “bent
pipe” design. Space switching means that the first satellite to receive the
call determines the destination of the call and sends the call via neighbor-
ing satellites until it is over a point on the Earth close to the destination. At
this point the signal is sent down to an Earth station and interconnected
with the PSTN or PLMN as appropriate. In a bent pipe system the satellite
just sends back to Earth the signal it receives from the mobile. The Earth
station near the mobile then uses the international fixed telephone net-
work to route the call to the called destination. Space switching has the
advantage of a reduction in cost because international calls are not
required, an increase in reliability because only one network is involved,
and a reduction in the number of Earth stations because it is not necessary
for each satellite to be able to see an Earth station. It has the disadvantage
of additional complexity in the satellite network that now has to be able to
provide a switching function and call routing to neighbor satellites. The
Iridium system uses switching in space. The bent pipe system has the
advantage of simplicity, resulting in relatively cheap and reliable satel-
lites, but the disadvantage that more Earth stations and international calls
are required. The Globalstar system is a bent pipe system.
There is a further issue to do with economics that has recently caused
the space switching systems much difficulty. Many PTOs, especially in
developing countries, make large profits from international calls that are
priced much higher than local calls despite the fact that the cost of provid-
ing them is only slightly greater.3Many of these international calls are
152 The Complete Wireless Communications Professional
3. For a further discussion of the issues of international call costs and subsidization, see [3].
generated by visiting businessmen. These countries are concerned that
the space switching systems will “steal” most of their international calls,
reducing their revenue. As a result, they have decided not to allow the
space switching operators access to the radio spectrum in their countries.
The bent pipe systems do not have this problem, since as long as there is
an Earth station in the country, the calls will be routed into the PSTN
locally, enabling the international calling rates to be achieved. This prob-
lem has caused the space switching operators to deploy more base stations
than is strictly required in order to cause more of the traffic to be routed
on the fixed networks, removing many of the advantages of space
switching.
This is an interesting lesson for the complete wireless professional.
The technical arguments proved to be irrelevant in the case of a distorted
pricing regime and the concerns of developing countries.
5.4.3 Economics of satellite systems
At the time of writing, in 1998, all the Iridium satellites were in place and
service was expected to start later in the year. The owners of Iridium have
spent an estimated $4B in putting their system into orbit and now need to
recover that cost. Opinion is still divided over whether satellite systems
can be profitable. Clearly the owners of Iridium have satisfied themselves
that their money is invested wisely. The basic selling proposition is that
users of Iridium or other satellite systems will be prepared to pay substan-
tially more for calls made from remote areas than cellular and wireline
phone users pay for their calls because there are no other options and
because the users will wish to stay in contact. Iridium may charge up to
$3 per minute to make a call on its phone. The question is whether there
are enough people in the world who regularly travel to places where their
cellular phones do not work and who would pay $3 per minute in order to
keep in communications.
Iridium claims that they only need around 700,000 customers each
paying an average of $3 a minute for their calls to repay the cost of the
system within three years. Given that the system cost is estimated to
lie between $4B and $8B, this would mean that revenues in excess of
$2,000 per subscriber per year would be required. This is not an unrea-
sonable expectation for senior management within companies. Iridium
will be targeting their system very much at global executive travelers
Other mobile radio systems 153
who require to stay in contact wherever they travel. With the launch of
Iridium services expected in September 1998, it will not be long before it
becomes clear whether this is a viable service capable of making signifi-
cant revenue.
5.5 TV, radio, and other
systems
TV and radio Television and radio do not obviously fit into the cate-
gory of mobile radio, although, stretching a point, the mobile reception of
TV and radio is widespread. However, the complete wireless professional
needs to know a little about this area because:
◗The advent of digital television will change the manner in which TV
and radio make use of radio spectrum;
◗Digital radio will allow the transmission of data to individual users;
◗TV and radio face the same propagation difficulties as mobile radio;
◗Many of the technical designs used for digital TV and radio are also
being proposed for cellular systems.
Current analog television systems work in a similar way to cellular
systems as far as the network design is concerned. Transmitters exist in a
cluster arrangement with a typical cluster size of 11. Given that transmis-
sion of an analog TV channel requires approximately 8 MHz of band-
width, to transmit a single channel nationwide requires 88 MHz of
bandwidth. Most countries typically deploy around four national chan-
nels in the UHF frequency band, between around 400 MHz and 800 MHz,
typically mostly filling this band when a few channels are set aside for
outside broadcast purposes and difficult coverage areas. The actual signal
transmitted is a complex composite analog signal containing luminance,
color, and sound information that is not discussed further here.
Television broadcasting is due to change in the next few years with
the introduction of digital TV. Digital takes advantage of the compression
that is possible on a TV picture in much the same manner that speech cod-
ers can compress voice signals. With TV, the current frame is almost
always nearly identical to the previous frame and, hence, if the difference
154 The Complete Wireless Communications Professional
between frames is transmitted rather than the actual frames, this allows a
dramatic reduction in the bandwidth required. However, like voice cod-
ing, the greater the compression, typically the lower the quality of the
final picture. Digital TV standards allow for a range of different coding
rates from around 1 to 8 Mbps. The lower rates are envisaged for lower
quality critical programs such as game shows whereas the higher bit rates
would be used for films and sporting events. As a result, the number of
channels available to the viewer to watch could change during the day as
the program content changes.
One of the key design decisions in both digital radio and digital televi-
sion has been the capability to deploy single frequency networks (SFNs). At
present, it could be argued that much spectrum is being wasted by analog
TV, which broadcasts the same signal in neighboring cells but needs 11
frequencies to do so.4Since the same information is broadcast in each cell,
in principle only one frequency should be required. However, to achieve
this with analog TV transmission would require careful design of quasi-
synchronous networks as discussed in Section 4.2 and even then would
typically result in significant “ghosting” for viewers. With the capability of
digital systems to process signals before they are placed on the screen, it is
possible to deploy SFNs.
The approach adopted to achieve this has been to transmit a short
pause after each bit is transmitted. This is shown in Figure 5.3.
In this figure, the first trace shows the signal from the nearest cell and
the second and third traces from neighboring cells that result in signals
with an increased delay (because they are further away) and a lower
power. The resulting signal seen by the receiver is shown in the bottom
trace. As can be seen, because all the echoes arrive before the next bit
from the nearest transmitter, they do not interfere with each other.
Indeed, by adding all the signals from each of the transmitters a stronger
overall signal is received, one that is less vulnerable to interference
because of the diversity of reception (from a number of transmitters).
However, the down side is obvious, the bandwidth required by the origi-
nal signal has increased significantly as a result of sending shorter pulses.
In the preceding example, where the pulse width was only one-fourth
Other mobile radio systems 155
4. This is not the case in the United States, where typically cities are sufficiently far apart
that the same frequencies can be deployed in each city without any interference. In
Europe, the population is more evenly spread and better geographical coverage is
required with the result that interference can become problematic.
of the total possible pulse width, the bandwidth requirement would
be increased by a factor of 4. Nevertheless, if this removed the need
for a cluster size of 11, the net gain in spectrum efficiency would be
11/4 =2.75 times.
156 The Complete Wireless Communications Professional
(a)
(b)
(c)
(d)
Figure 5.3 The signal received in an SFN: (a) the signal from the
closest transmitter, (b) the signal from the second closest transmitter,
(c) the signal from the third closest transmitter, and (d) the composite
signal as seen by the receiver.
Some simple calculations reveal further problems with this arrange-
ment. If it is assumed that interfering base stations might be up to, say,
50 km away, then the delay on receiving a signal from these base stations
will be around 0.2 ms. If there needs to be a delay of 0.2 ms after the trans-
mission of each pulse, then even if the pulse length is negligible this limits
the data rate to 6k baud. Even with the proposed 16- and 64-level quadra-
ture modulation, allowing four or six bits per symbol, respectively, this
still only allows a maximum data rate of around 24 or 36 kbps, far too low
for the transmission of digital video.
The solution to this problem has been to split the data to be transmit-
ted into a large number of streams and to encode and transmit each of
these streams separately. Using up to 8,000 separate streams, the data rate
on each stream can be brought well within the limits calculated previ-
ously. Such an approach is well known from mobile radio research as
orthogonal frequency division multiplexing (OFDM), even if it has never been
deployed in a commercial mobile radio system. In a practical arrange-
ment, OFDM works by passing the incoming data through a Fourier
transform (which has the same effect as splitting it into a number of
streams), transmitting the resulting data, and then performing an inverse
Fourier transform on the received data in order to arrive back at the origi-
nal information. OFDM is a complex topic that is discussed in more detail
in [5]. In summary, the key differences between digital radio and TV
transmission and cellular are the use of OFDM and the use of QAM.
Mobile radio systems do not need OFDM because there is no possibil-
ity of an SFN since different information is transmitted in each cell. They
tend not to use quadrature modulation because the quality of the mobile
radio channel is so poor that it is not possible to accurately distinguish
between a number of different modulation levels. For a more detailed dis-
cussion of the issues surrounding the use of QAM, see [5].
Despite the fact that, in principle, the introduction of digital TV should
result in a dramatic improvement in the spectrum efficiency and hence
the possibility that some spectrum could be returned to the regulator and
then possibly assigned to cellular operations, it is still far from clear
whether this will be the case. The arguments are complex and beyond the
scope of the discussions here, but some of the key points include:
◗More spectrum than at present will be needed during the transition
from analog to digital when simultaneous broadcasting on both
Other mobile radio systems 157
formats will be required and this transition could take as long as
15 years.
◗Digital TV will need to offer many more channels than the current
analog TV in order to persuade viewers to buy a new TV set.
◗Digital TV enables new facilities such as home shopping, which may
require additional bandwidth.
◗SFNs may not be suitable for all channels because they do not allow
regional variations such as local news and different advertisements
in different regions as are currently transmitted.
Other users of the radio spectrum There are many other users of
the radio spectrum with which the complete wireless professional only
needs a passing familiarity.
◗Aeronautical radio and radar for civil aviation purposes—in par-
ticular, the aeronautical radar and instrument landing systems take
up a large amount of spectrum below 2 GHz;
◗Military usage, which tends to be confidential but uses a large per-
centage of the spectrum under 2 GHz;
◗Fixed link usage (fixed links are discussed in Section 7.1.5), which
can be used to support mobile radio networks; fixed link bands
extend from 2 GHz upward;5
◗Amateur and research users, which have small assignments
throughout the mobile spectrum band;
◗Industrial, scientific, and medical (ISM) uses, which include, for exam-
ple, the use of radio to dry leather hides and heat certain products;
this band is unlicensed and recently a number of WLL operators
started using the band for communications, using frequency hop-
ping and CDMA technology to overcome the unknown and time-
varying interference.
158 The Complete Wireless Communications Professional
5. In some cases, mobile radio engineers may have to interwork with fixed links. For
example, in the U.S. PCS bands, the spectrum was sold to the mobile radio operators with
fixed links already in the bands. The operators had to decide whether they would work
around the fixed links or pay the fixed links operators to move to a different band. This
legacy use of the band continues to cause interference problems.
For more details about the use of the radio spectrum in any particu-
lar country, the national spectrum manager can normally provide
the required information. For example, complete details of all spec-
trum allocations in the United Kingdom can be found from the U.K.
Radiocommunications Agency [6] while details of U.S. allocations can be
found from the FCC [7].
References
[1] Tuttlebee, W., ed., Cordless Telecommunications Worldwide, Berlin:
Springer-Verlag, 1997.
[2] Phillips, J. A., and G. Mac Namee, Personal Wireless Communications with DECT
and PWT, Norwood, MA: Artech House, 1998.
[3] Webb, W., Introduction to Wireless Local Loop, Norwood, MA: Artech House,
1998.
[4] Jamalipour, A., Low Earth Orbital Satellites for Personal Communication Networks,
Norwood, MA: Artech House, 1997.
[5] Webb, W., and L. Hanzo, Modern Quadrature Amplitude Modulation, New York:
John Wiley, 1994.
[6] Information can be found at
http://www.open.gov.uk/radiocom/rahome.htm, which also
contains links to most other spectrum managers around the world.
[7] The FCC website can be found at http://www.fcc.gov.
Other mobile radio systems 159
Interfacing with
fixed networks
Co-existence: what the farmer does with the
turkey—until Thanksgiving.
John Berry
6.1 The need for fixed
networks
The complete wireless professional needs to
know all about fixed networks. At a mini-
mum, the mobile radio network will typically
need to be connected to a fixed network at
some point. Further, interconnection of dif-
ferent parts of the mobile radio system may be
via fixed networks. Fixed networks are com-
plex topics and a good introduction to them
can be found in [1, 2].
Important points to understand about
fixed networks are:
◗The outline architecture of a fixed network;
161
Contents
6.1 The need for fixed
networks
6.2 Fixed network
architectures
6.3 Fixed network
protocols
6.4 Fixed mobile
convergence
6
CHAPTER
◗The concept of intelligent networks since future cellular system
design will need to incorporate intelligent network philosophies;
◗How numbering and addressing schemes are devised since mobile
radio systems need to be part of these;
◗The basic interconnection mechanism using E1 or T1 links;1
◗The many different protocols that are in use on the fixed net-
works and the most appropriate protocols to use in any particular
situation;
◗The convergence of fixed and mobile networks expected to occur
over the coming years.
6.2 Fixed network
architectures
Outline In outline, a fixed network consists of one or more switches, a
number of distribution points, and wires to each of the subscribers’ prem-
ises. The distribution points are used to gather a number of subscriber
connections into a larger bundle of cables that can then be more easily
routed back to the switch. Each switch is likely to be connected to a
number of other switches using diverse routing that allows an alternative
to be found in the case of failure of a single link.
Modern networks are constructed either on a circuit-switched or a
packet-switched principle. In circuit switching, a dedicated circuit is
established between the two users for the duration of the call. In a
packet-switched system, packets are sent whenever there is information
to be conveyed and these are routed along a shared resource by the net-
work. The PSTN is a good example of a circuit-switched network, whereas
the Internet is a good example of a packet-switched network. Both will be
discussed in this section.
Switch design Switch design is complex and a detailed description
is beyond the scope of this book. Simplistically, in the case of circuit
switching, the switch works by overlaying all the incoming lines over all
162 The Complete Wireless Communications Professional
1. The decision as to whether to use the T1 or E1 standard is typically made on a regional
basis, with T1 being used in the Americas and E1 in Europe.
the outgoing lines in a grid structure and pulling together the lines at the
crossover point when a connection is required. However, such a simple
switch rapidly becomes unmanageable as the number of cross-points
increases by the square of the number of incoming lines. Switches were
only designed in this manner until around the middle of this century. The
next generation of switches used the principle of fan-in and fan-out
where the incoming lines were switched onto a smaller number of inter-
nal lines when a call was taking place. This smaller number of internal
lines was then switched across the outgoing lines. For example, in the
case of 10,000 incoming and outgoing lines, in a simple exchange
100,000,000 cross-points would be required. For 10,000 incoming
lines with a typical traffic level the Erlang formula predicts that about
560 lines will be required to produce acceptably low levels of blocking. At
the fan-in point the 10,000 lines cross with the 560 lines, and at the
fan-out point the same number of cross-points are required. The total
number of cross-points needed is 2 ×560 ×10,000 =11,200,000, only
around 10% of the number of cross-points required in the first case. All
these types of switching are referred to as space switching because a
switch taking up a certain amount of space connects and disconnects
physical resources.
Modern switches use digital switching in a time-space-time format.
This takes into account the fact that the incoming lines are typically E1s
on which the calls are encoded using TDMA. A modern switch needs to be
able to take the incoming signal on, say, timeslot 6 of a particular E1 link
and to pass it to, say, timeslot 18 of a particular outgoing link. Hence the
need to switch first in time, second in space, and third back in time again.
A simplified diagram of a time-space-time switch is shown in Figure 6.1.
In this switch, an incoming call on timeslot 3 of incoming line 1 is first
switched in time to timeslot 30. Then the entire E1 on the left side of the
switch is mapped onto the E1 on the right of the switch corresponding to
outgoing line 2. Timeslot 30 is then mapped onto the final timeslot used,
timeslot 1, on the outgoing line. In practice, such an arrangement would
not work since it might be required to switch timeslot 3 onto outgoing line
2 but timeslot 4 onto outgoing line 1. Hence, the space switching part can
switch 32 times within a frame so that incoming line 1 is connected to
outgoing line 2 during the 8 bits corresponding to timeslot 3 but then con-
nected to outgoing line 1 during timeslot 4. Such a switch has a similar
advantage to the fan-in fan-out switch in that the number of cross-points
are significantly reduced. Most modern digital switches are designed
along this principle.
Interfacing with fixed networks 163
164 The Complete Wireless Communications Professional
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
0
1
2
3
31
Time
switch
Time
switch
Time
switch
Time
switch
Time
switch
Time
switch
Incoming
line 1
Incoming
line 2
Incoming
line 3
Outgoing
line 1
Outgoing
line 2
Outgoing
line 3
Space switching part
Figure 6.1 A simplified time-space-time switch.
In the case of a packet switch, a somewhat different arrangement is
required. A packet switch receives incoming packets and stores them in
an input buffer. It then reads packets out of the buffer, examining the
address on the front of each packet. Based on the address, the packet is
then sent out on the most appropriate output line. Because of the ability
to tolerate a short delay, and hence the need to process only one packet at
any particular point in time, packet switches can be considerably simpler
than circuit switches.
Intelligent networks Modern fixed networks are constructed
around an intelligent network (IN) philosophy, and increasingly mobile
radio networks are also starting to be designed around the same philoso-
phy. INs are intended to allow the easy introduction of new services with-
out the need to replace or upgrade switches. Essentially, an IN separates
out the hardware and the software in a network, allowing new software
to be written when new services are required. To work effectively, INs
need a standardized software language, a basic “operating system,” and a
means of introducing new software onto the network. The IN standards
cover these areas. The benefits of intelligent networks are intended to be:
◗The rapid introduction of new services with minimal impact on the
existing architecture through the downloading of new service script
software;
◗The reduced cost of introducing and enhancing new services;
◗The ability to rapidly reconfigure services to meet market needs;
◗The ability to give limited control to selected customers so they can
make authorized changes specific to their own network—an exam-
ple of this might be a company subscribing to a centrex service and
making some changes to the manner in which certain numbers are
processed.
The conceptual model of the IN as envisaged by current standards
bodies has four planes, each representing different levels of IN abstraction
as shown diagrammatically in Figure 6.2.
The service plane represents a service-oriented view of the IN and does
not contain any information regarding the implementation of the net-
work services. This would contain a list of all the services available, along
with an associated list of all the functions that they must call. For
Interfacing with fixed networks 165
example, there would be an entry for call redirection alongside its access
code, say, *50. Such a function might require an announcement and a call
translation.
The global functional plane resides below the service plane and pro-
vides a view of different functional entities of an IN network. The plane
contains the call-processing model and service-independent building blocks
(SIBs). Example SIBs are: announcement, a feature that may be required
by a wide range of services; information input through the numeric key-
pad, again a widely used function; and charging procedures, for example.
The SIBs are defined independently of any physical consideration. SIBs
are used as building blocks in the creation of services.
The distributed functional plane resides below the global functional
plane and is used to define the functional entities (FEs), their actions
(FEAs), and their relationships and information flows. The functional
entities translate the non-network specific SIBs into physical commands
that can be sent into the network to accomplish tasks. It is within this
plane that the details of alternative networks start to differ.
Finally, the physical plane identifies the different types of physical enti-
ties and their information flows. It contains all the peripherals and control
166 The Complete Wireless Communications Professional
Service plane
Global functional
plane
Distributed
functional plane
Physical plane
List of all
available
service
Call re-
direction
Call
processing
model and
SIBs
Announcement
Functional
entities and
actions
Physical
entities
Speech
synthesizer Tone
generator
Keypad
input
Translate standard
announcement messages to
actual network commands
On-line
billing
information
Figure 6.2 Conceptual model of the IN services.
nodes that form the structure of the network and are used to carry and
process the information.
A functional model of an IN is given in Figure 6.3. Calls are routed
from user to user through the service switching point (SSP), effectively the
standard network switch upgraded to IN functionality. This unit has the
capability to detect a requirement, or trigger, for an IN service. Requests
for IN functions are then formulated and passed either to the service control
point (SCP), services node, or adjunct, depending on network implemen-
tation. These requests are sent using CCITT7 signaling using special parts
designed for IN called the signaling connection and control part (SCCP), the
transaction capability application part (TCAP), and the intelligent network
Interfacing with fixed networks 167
Operations
systems
Service
control
point
Service
switching
point
Adjunct
End
office
Intelligent
peripheral
User User
User
Legend:
Transport
Operations
Signaling
Figure 6.3 Functional model of an IN.
application part (INAP). SCPs are connected through common channel sig-
naling (CCS) networks that allow a number of SCPs to be interconnected.
This is used when accessing centralized databases or for person locator
services. Interaction with users is provided through the intelligent periph-
eral (IP), which can issue voice messages to the user and accept key pad or
conceivably voice inputs. The IP receives instructions from the SSP and
relays received responses back to the SSP.
For mobile communications, all the functions of the IN described pre-
viously are still applicable. In addition, there may be a need for IN func-
tions to allow mobility and call management. These include location
information retrieval and updating on call routing, handover, charging,
and maintenance. These additional service features could result in dra-
matic increases in service traffic, especially as cell sizes reduce and mobile
densities increase, causing frequent location updating for a large number
of users. Current mobile systems incorporate the functions mentioned
previously into their own pseudointelligent networks, leading to the pos-
sibility of two INs, one in the mobile system and one in the PSTN to which
it is connected. It is the view of the fixed link community that these
should be integrated into one IN in the future. For this to happen,
more integration between fixed and mobile standards authorities will be
required.
Telecommunications management network The telecommunications
management network (TMN) is intended to be a means to allow the effec-
tive management of networks. Network management is discussed for
mobile radio networks in Section 9.2. TMN is the equivalent for the fixed
network. The basic problem with existing fixed networks has been that
the various parts of the network often come from different suppliers; for
example, the switch may be manufactured by someone different from the
synchronous digital hierarchy (SDH) link. Each manufacturer will provide a
network management system for their part of the network, but these will
typically not interwork. The result is a proliferation of different manage-
ment systems; and because they do not interwork, a fault in one part of
the network can result in alarms appearing on a number of different net-
work management systems, taking the manager of the network some
time to determine where the fault actually lies. TMN presents a standard-
ized interface to which all the manufacturers can pass information
concerning their part of the network. This allows a single network
168 The Complete Wireless Communications Professional
management system to be used. TMN relies on an interface defined as the
Q3 interface, the common management information protocol (CMIP), and
managed objects (MOs).
Numbering and addressing plans All telephones, including mobile
phones, need a unique number. The administration of a numbering plan
is important for the continued operation of the world’s telephone net-
works. The most relevant addressing scheme for mobile radio is the ITU-T
E.164 recommendation. This recommends the 00 international prefix,
the 0 prefix for trunked calls, and a maximum length, excluding interna-
tional prefix of 15 digits. The structure of an E.164 number is shown in
Figure 6.4.
E.164 allows a number of key features.
◗Direct dial in allows the last few digits at the end of an ISDN number
to be transferred to a customer’s PABX, enabling the call to be fur-
ther routed inside the company without a switchboard operator.
◗Subaddressing allows up to 40 additional digits to be added on top
of the ISDN number to allow further routing on the customer
premises.
Interfacing with fixed networks 169
International
prefix 00 Country code
CC
National significant number (NSN)
(trunk area code plus subscriber code)
Maximum 15 digits
Trunk prefix
0
National significant number (NSN)
(trunk area code plus subscriber code)
Structure of an international telephone number
Structure of a national telephone number
Figure 6.4 Structure of national and international telephone
numbers.
6.3 Fixed network protocols
The mobile radio engineer will not typically be concerned with the proto-
cols that are used between the fixed phone and the switch because this is a
topic for the fixed telecommunications engineer. However, a knowledge
of the protocols running between the switches is important since this is
the manner in which the mobile radio network will be interconnected
into the PSTN. This section provides an overview of the protocols in use.
The basic framing structure On fixed lines, voice is typically carried
at 64 kbps using PCM coding. Lines between switches are used to carry a
number of voice channels. The European standardized rates for these
links are:
2.048 Mbps termed an E1 link
8.448 Mbps termed an E2 link
34.368 Mbps termed an E3 link
139.264 Mbps termed an E4 link
564.992 Mbps termed an E5 link
In the United States there is a different nomenclature:
1.544 Mbps termed a T1 or DS1 link
6.312 Mbps termed a T2 or DS2 link
44.736 Mbps termed a T3 or DS3 link
139.264 Mbps termed a DS4 link
These two systems are incompatible at all levels, but protocol convert-
ers now exist that allow one system to be connected to the other. How-
ever, in the connection process, channels typically have to be wasted; for
example, when connecting an E1 to a T1, two T1s are required, providing
a total bandwidth of 3 Mbps, of which 1 Mbps remains unused.
Higher rate links are assembled by multiplexing from lower rate links.
For example, an E2 is obtained by multiplexing four E1s together and an
E3 by multiplexing four E2s. Hence, for the higher rate links, there may
be a significant hierarchy of multiplexers and demultiplexers required to
extricate the data for one particular user. For the remainder of this chap-
ter, the European E1 system is used for further discussion. However, the
U.S. system is very similar in design, and most of the points apply equally
to the U.S. system.
170 The Complete Wireless Communications Professional
The E1 carrier has a strict framing format. It consists of a framing
structure, similar to the TDMA framing structure of GSM, as described in
Chapter 3, which repeats every 125 µs. This frame is divided in 32 times-
lots marked timeslots 0 to 31. Within each timeslot, eight bits from each
user are transmitted. Of these 32 timeslots, only 30 can be used to carry
user data. Timeslot 0 contains a flag used to signal the start of a new frame
while timeslot 15 is used for signaling purposes. The signaling informa-
tion is used to set up a call on any of the other timeslots within the E1 and
will contain information about the destination of the call and the timeslot
on which it will be carried. Timeslot 0 is also used for synchronization
purposes. The two switches interconnected by the E1 link will often be
using different clocks. Although every effort is made for the clocks to
be running at the same speed, they are not actually synchronized and
are often termed plesiochronous to indicate that they are unsynchro-
nized but adjusted to run as closely to each other as possible. In the case
that the clock in the transmitting exchange is running faster than
the clock in the receiving exchange, more bits are sent than can be
received. To overcome this, the receiving exchange can simply remove
some of the bits in timeslot 0. In the opposite case, the receiving
exchange can add some extra bits into timeslot 0 to make up the rate. An
E1 system of this form is said to belong to the plesiochronous digital
hierarchy (PDH).
More modern systems are designed using fully synchronous net-
works and are referred to as being part of the SDH or synchronous optical
network (SONET). In these systems all the different exchanges must use
the same clock. Typically, in any country there will be a master clock. This
master is transmitted via wire to each of the exchanges directly below it in
the hierarchy. Each of these exchanges then further distributes the clock.
They also typically have their own clock that is tied to the master clock
but, in the case of loss of master clock, can continue to run so that the tele-
phone system can continue to work. Different countries can choose to
link their master clocks if required so that they are synchronized. More
recently, another option has been to use the timing reference transmitted
by the GPS as the clock source at each of the exchanges. SDH has a major
advantage over PDH in that single channels can be inserted into and
removed from the stream without the need to demultiplex back to an E1
prior to removal or insertion. Demultiplexing is necessary in PDH in order
to remove the additional framing bits according to the difference in clock
Interfacing with fixed networks 171
rates at each of the various level but is not required in SDH. Because of
this advantage, most modern systems are synchronous.
Interexchange signaling It was mentioned previously that timeslot
15 on the E1 link is reserved for signaling associated with setting up calls.
An agreed protocol is required for this signaling such that different
exchanges can interwork. There are a number of different protocols that
can be used for this purpose. Some of the key ones are:
◗CCITT6: A common channel signaling system for use between ana-
log exchanges with a signaling speed of 2.4 kbps;
◗CCITT7: A complex and multipurpose common channel signaling
system for use between digital exchanges with a signaling speed of
64 kbps;
◗CCITT R1: A regional signaling system formally used for trunk sig-
naling in North America;
◗CCITT R2: A regional signaling system used within Europe.
Some of the key signaling protocols are described in more detail.
The R2 signaling system R2 is a form of channel-associated signal-
ing that means all the signaling that is relevant to a particular channel
passes down that channel itself. This differs from the E1 arrangement
described previously where there is a separate signaling channel for the
30 connections carried on the link. Before digital exchanges were wide-
spread, associated channel signaling was the only possible way of trans-
mitting signaling information, but it has the disadvantage that a separate
signaling “reader” is required on every single line, whereas with common
channel signaling the number of readers is considerably reduced (by a
factor of 30 in the case of the E1 arrangement)—hence, the trend in mod-
ern systems toward common channel signaling. R2 line signaling is car-
ried out of band in tones at 3,825 Hz that are filtered out in the receiving
device that only allows voice signals in the band 300 Hz to 3.4 kHz to pass.
By being out of band, the signaling does not disturb the voice traffic but is
restricted to a low data rate. The signaling used is relatively simple, mov-
ing a state machine through six different states as shown in Table 6.1.
R2 works by sending a signal (setting the tone on or off) until a sig-
nal is received from the other end. The received signal both acts as a
172 The Complete Wireless Communications Professional
confirmation and allows the state machine to be moved to the next state.
This acknowledgment process is known as compelled signaling.
There is also a multiple frequency version of R2 where the signaling is
carried in band during the set up of the call and can be used to carry the
dialed number. This signaling system is known as R2 MFC. R2 is only of
interest when needing to interface with older exchanges; modern digital
exchanges will typically make use of CCITT7 signaling.
Integrated services digital network The integrated services digital
network (ISDN) is a network providing end-to-end digital connectivity to
the user [3], unlike most fixed connections at the moment that are analog
and require modems to transmit digital data. ISDN provides the services
of voice, 64-kbps data, facsimile, telephony, and video-telephony as well
as a range of supplementary services. ISDN standards are set worldwide
by the telecommunications division of the International Telecommunica-
tions Union (ITU-T) and contain two types of customer-to-network inter-
faces: the basic rate access (BRA) and the primary rate access (PRA). Both
consist of a number of bearer (B) channels at 64 kbps and a data (D) chan-
nel at either 16 or 64 kbps, which is not actually used to carry user
data but only to carry signaling relating to the call. BRA consists of
2B +D channels, using a 16-kbps D channel; whereas PRA consists
of 30B +D channels, using a 64-kbps D channel. In order to install BRA
ISDN at a user’s premises, the bandwidth of the subscriber connection must
be increased to allow 144 kbps. This is achieved by removing loading coils
on the circuit but may not be possible for all installed lines; hence, it may
not be possible to universally install ISDN to all subscribers. PRA, at 2 Mbps
typically requires a special connection, although with the advent of new
Interfacing with fixed networks 173
Table 6.1
The Use of Tone Signaling in R2
State Outgoing Tone Incoming Tone Meaning Moves to State
1 On On Circuit idle 2 or 6
2 Off On Seized 3 or 5
3 Off Off Answered 4 or 5
4 Off On Clear 3 or 5
5 On Any state Release 1
6 On Off Blocked 1
digital subscriber line technologies (see Section 5.3.2), it is becoming
increasingly possible to carry these rates across some standard telephone
lines. ISDN has the advantage that a BRA can be used to send two simulta-
neous messages; for example, one of the B channels could be used for
voice and the other for data. However, when only one line is in use, the
two available channels can be combined to achieve a higher data rate
than would have been possible on one channel alone.
In order to support ISDN a digital switch is required. The switch must
use 64-kbps digital voice channel switching and support common chan-
nel signaling between exchanges. Typically, the interswitch protocol
adopted is CCITT7 along with the specific part of the standard required for
ISDN, the integrated services user part (ISUP).
Signaling system No. 7 CCITT7 is also widely known as SS7 (and
C7). Most digital telephone networks around the world make use of SS7.
It is essentially a common channel signaling system that enables two digi-
tal exchanges to communicate directly and interact in a manner that
allows digital transmission. SS7 is designed in a layered and modular
manner and can support a range of applications including:
◗ISDN;
◗Intelligent networks;
◗Mobile services;
◗Network operation and management.
New user parts can be written to support new applications (e.g., dur-
ing the standardization of GSM, the mobile application part (MAP) was
written to allow MSCs to interconnect using SS7). The existing user parts
include:
MTP message transfer part
SCCP signaling connection and control part
TUP telephone user part
DUP data user part
ISUP integrated services user part
TCAP transaction capabilities application part
OMAP operations and maintenance application part
INAP intelligent network application part
MAP mobile application part
174 The Complete Wireless Communications Professional
The MTP and the SCCP are the basic parts of the system allowing mes-
sage sending. The other parts tend to use MTP and SCCP to carry their
higher level messages. Between two SS7 switches there will be a signaling
network and a traffic carrying network. In most cases these will be inte-
grated within the same E1 connection, but this need not be the case and
the signaling network can be quite separate from the traffic network.
Worthy of a short mention is MAP, the signaling system in use by
newer digital mobile radio networks. It is used between a mobile tele-
phone network exchange (normally known as an MSC) and an intelli-
gent network database (the HLR, VLR, or EIR). MAP allows interrogation
of these databases and responses returned in an appropriate format.
X25 X25 is a protocol for packet switching networks and controls the
manner in which computers producing packet information interwork
with the packet network. Some aspects of X25 are used within the GSM
network when sending signaling information related to, for example, call
setup between the switch and the BSS. X25 is a connection-oriented pro-
tocol. At the start of a session a virtual circuit is established before data are
transmitted. Packets of data may be anything between 3 and 4,100 bytes,
allowing up to 4,096 ASCII characters to be sent in one packet. A basic
packet consists of an 8-bit flag (with bit pattern 01111110), an 8-bit
address, 8 bits of control information, the user data, and a 16-bit frame
check sequence that detects whether there have been errors in the
received data. The address field is only used to determine whether the
information is a command or a response, the address details of the user
already having been established at the time that the virtual channel was
set up. X25 is probably the most widely used packet switching protocol
to date.
The strength of X25 networks is their high reliability in transporting
data accurately across lines even with high error rates, whereas their
weaknesses lie in the high delays that can be incurred on data transmis-
sion, which is becoming increasingly problematic on computer data
exchange.
Frame relay Frame relay has come about due to the shortcomings in
X25, as mentioned previously. X25 was developed at a time when signal-
ing rates were around 9.6 kbps and errors on lines were frequent. X25 is
less suited for today’s high-speed, high-reliability lines. Packet transmis-
sion on high-quality lines does not require the acknowledgment and win-
dowing provided by X25. Frame relay leaves the task of error correction
Interfacing with fixed networks 175
and acknowledgment to the higher layers, concentrating only on rapid
transfer of the raw information. Because it does not need to wait for
acknowledgment or check for errors, transmission can be much more
rapid. Frame relay is well suited to data rates of between 64 kbps and
2 Mbps and in applications such as LANs and wide-area computer net-
works. Above 2 Mbps, ATM is more appropriate. Frame relay includes
network management to cope with information overload in the cases that
there is a sudden increase in the information being sent from the comput-
ers linked to the network. Frame relay makes use of a committed informa-
tion rate (CIR) that is agreed upon between the network and the users at
the time that the connection is set up and guarantees a minimum rate.
The network also agrees on an excess information rate (EIR), higher than the
CIR, at which information can be transmitted when there is capacity on
the network. As the network becomes heavily loaded, explicit congestion
messages (ECMs) are sent to the users, who should reduce their transmis-
sion rate to the CIR.
The frame format for frame relay is very similar to the format used in
X25. There is a flag, address, control field, information field, and frame
check sequence. The information field can be up to 65,536 bytes in
length.
TCP/IP The transport control protocol/Internet protocol (TCP/IP) [4] was
developed from the UNIX-based computers used by government and aca-
demic institutions at the time that the Internet started to emerge. Unlike
the other packet protocols discussed briefly here, TCP/IP is a connection-
less protocol, so each packet is treated as a completely separate entity by
the network. The Internet protocol is the equivalent of an OSI layer 3 pro-
tocol, where the 7-layer OSI stack is shown in Figure 6.5, while TCP pro-
vides the layer 4 functionality. An Internet data message is quite complex.
The framing format includes the header length, the type of service, the
total length, the identification, flags, a field describing how long the mes-
sage should be held before being deleted in the case of delivery being
problematic, protocol details, a header checksum, source and destination
addresses, options padding, and finally the user data. Addresses are pro-
vided as 32-bit information in the form 123.234.200.134, where the four
numbers can each have values up to 255.
Asynchronous transfer mode ATM is a connection-oriented packet
switching protocol designed for the rapid transmission of data in broad-
band networks [5, 6]. ATM was designed to allow:
176 The Complete Wireless Communications Professional
◗The simultaneous transmission of different telecommunications
services;
◗A contract established at connection setup that allows the end user
to specify the required bit rate and connection quality including
details as to the maximum permissible delay;
◗The ability of the network to determine when new connections
cannot be granted because the load on the network is such that con-
tracts might not be met if new loads were accepted;
◗The ability to carry delay-sensitive voice and video traffic with a
minimal delay;
◗A high efficiency in the use of bandwidth.
Interfacing with fixed networks 177
Application
Presentation
Session
Transport
Network
Data link
Physical
OSI layer
number
1
7
6
5
4
3
2
Application
Presentation
Session
Transport
Network
Data link
Physical
Peer-to-peer
communications
Actual communications
Imaginary communications
(relying on lower layers)
Figure 6.5 OSI standard layered model of a telecommunications
network.
Unlike the other packet protocols discussed, ATM uses packets of a
fixed size. These contain a 5-byte header and 48 bytes of user data. The
small size of the packets requires that most information is broken up for
transmission but ensures that high-priority frames do not have to wait for
the passage of a large frame before they can be transmitted, thus allowing
guaranteed low delays for some traffic. ATM is the most appropriate
packet protocol to use for transmission rates above 2 Mbps. Because of its
low delay, it can carry information that would normally have been passed
down a circuit-switched protocol and so can replace both packet- and
circuit-switched protocols on high speed lines.
6.4 Fixed mobile convergence
6.4.1 Introduction
Fixed mobile convergence (FMC) is a much talked about, although often con-
fused, topic, relating to the concept that instead of fixed and mobile net-
works being separate entities, as is the case now, they will converge over
the coming years. This section provides an overview of the possible means
by which FMC might be achieved, their advantages and disadvantages,
and their likely progress over the coming years. The section starts with a
definition of fixed mobile convergence and then moves on to examine the
currently identified solutions of:
◗Network overlay solutions to give the appearance of FMC;
◗Network integration solutions that put some of the mobile and
fixed functionality on a joint platform;
◗Solutions that integrate cordless and mobile technologies to pro-
vide a single phone;
◗Substitution solutions that attempt to carry all the traffic on the
mobile network.
The section then concludes with some predictions as to how the FMC
market will develop over the coming years.
178 The Complete Wireless Communications Professional
6.4.2 Defining fixed-mobile
convergence
FMC is the interworking of fixed and mobile telecommunications. At
present, FMC is mostly concerned with voice, and the simplest FMC con-
cept is that an individual has a single phone number that people can dial
and result in his or her fixed or mobile phone ringing as is appropriate.
This concept is readily extended to fax and data calls, with these calls
being routed to appropriate computers or fax machines depending on the
location of the called party. Finally, the convergence should allow for
there to be one voicemail box that can be accessed from both the fixed and
the mobile phone.
Complexity arises from the use of FMC by different parties. For the
fixed provider, FMC is a tool by which they can prevent traffic migrating
onto mobile networks by providing enhanced functionality that will
encourage the user to use the fixed phone whenever possible. For mobile
providers, FMC is a tool they can use to steal traffic from fixed networks
by offering the equivalent of a fixed service on the mobile phones. For the
fixed provider, FMC is the bringing together of fixed and mobile commu-
nications on the same platform, whereas for mobile providers it is the
avoidance of making or receiving calls on the fixed platform.
Despite this difficulty, the overriding concept is that the functionality
that the user experiences should be as if they only had one phone, regard-
less of how this is achieved.
6.4.3 Possible solutions
There are a number of different possible solutions to FMC. In this section,
the following four solutions are examined that cover the range of differ-
ent possible means to achieve FMC:
◗Network overlay solutions to give the appearance of FMC;
◗Network integration solutions that put some of the mobile and
fixed functionality on a joint platform;
◗Solutions that integrate cordless and mobile technologies to pro-
vide a single phone;
Interfacing with fixed networks 179
◗Substitution solutions that attempt to carry all the traffic on the
mobile network.
In many cases, these solutions can be used in combination as well as
in isolation; for example, network overlay solutions can be coupled with
the network integration solutions.
6.4.3.1 Network overlay solutions—the personal assistant
Definition The overlay solution or personal assistant is an IN function
that resides typically in the fixed network. A user has a single number that
directs the call to the personal assistant. Once it arrives there, it can
be redirected to the fixed line, mobile, voicemail box, fax machine, or
appropriate computer. The redirection is typically performed based on
information provided by the user such as their likely movements and a
knowledge of whether the mobile is contactable. In some cases, the call is
first directed to the fixed line and, if not answered, is redirected to the
mobile. A very simple way to achieve almost the same functionality is to
forward the fixed phone to the mobile phone when leaving the office.
◗Cost: This capability is relatively inexpensive to provide, requiring
only an IN platform. In the case of calls that terminate on the fixed
network, virtually no additional routing is required. For calls that
terminate on the mobile network, some additional routing into the
mobile network may be required.
◗Call billing: Since it is not known to the caller whether the call will
terminate on a fixed or mobile phone, either all calls to personal
assistants must be made more expensive or the called party must
pay an additional fee for incoming calls that were redirected to the
mobile phone. In the case of call-forwarding from the fixed to the
mobile phone, the called party pays for a mobile call for all incoming
calls.
◗Supplier capability: This service can either be provided by the fixed
network operator or a third party supplier of value-added services.
In a liberalized environment there is the possibility of competition
in the provision of personal assistants.
◗Revenue potential for operator: In principle, the personal assistance
might result in fewer calls, since fewer messages are now left on
180 The Complete Wireless Communications Professional
voicemail. However, by charging calls at a premium rate there is
potential for the service provider to make increased revenue.
◗User needs: This service provides the primary requirement of a single
telephone number. However, the user needs to interact with the
call redirection system to ensure that calls are directed appropri-
ately depending on time of day and location. There is typically a
delay in call setup that can be annoying for callers while the assis-
tant determines the type of call and appropriate destination.
◗Regulatory barriers: There are few regulatory barriers. It is helpful to
have the ready availability of personal numbers and to have a liber-
alized environment where service providers can interact with the
fixed network operator in able to ensure competition.
Advantages This service can be provided with little change to the net-
work and at a relatively low cost. It meets the fundamental requirement
of FMC and can be provided in a competitive manner.
Disadvantages The service is typically more costly than the status
quo. The need for intelligent call redirection can be tiresome for the user
and result in call setup delays.
6.4.3.2 Network integration solutions—joint platforms
Definition An operator who owns both a fixed and a mobile network
integrates as many of the functions of the networks as possible onto joint
platforms. Typically, the first function that is integrated is billing, result-
ing in a single bill for both fixed and mobile usage. Following from this,
voicemail and IN services can be integrated. Finally, it may be possible to
integrate some of the operations and maintenance and switch functional-
ity. Since this form of FMC does not allow for a single number for fixed
and mobile services, it does not strictly meet the definition of an FMC
service. However, it can, of course, be linked with an overlay-type IN
solution providing the functionality described previously.
◗Cost: The cost to the operator is in the procurement of platforms able
to handle fixed and mobile services. However, in the long term the
consolidation of platforms is likely to result in a cost reduction for
the operator.
Interfacing with fixed networks 181
◗Call billing: Billing for incoming calls is unaffected since this form of
FMC does not provide a single number.
◗Supplier capability: This can only be provided by the PTO in a country
and only then if they also have a mobile network. Since only a sub-
set of the mobile subscribers in the country will be using that par-
ticular mobile network, this will only be available to a minority of
the population.
◗Revenue potential for operator: There is little potential for increased
revenue. The only possibility is reduced churn from the mobile
users as a result of the enhanced service that they are being
provided.
◗User needs: Few of the user’s needs are met. The only distinguishing
feature for many users is the delivery of a single bill. This is gener-
ally thought to provide little added value.
◗Regulatory barriers: There are no barriers for the PTO. Unless there is
liberalization that has resulted in a significant competitor to the
PTO, there will be no other company able to provide the service.
Advantages This provides potential cost savings for the operator and
the advantage of a single bill for the user.
Disadvantages This solution does not provide a single number and,
hence, does not meet the requirements of FMC.
6.4.3.3 Advanced network convergence—DECT/GSM
integration
Definition This is a solution proposed by BT under the name
“OnePhone.” The concept is that DECT cordless base stations are installed
within the office and are connected to the existing fixed lines into the
office. The DECT system is then connected into the GSM switch of a
mobile operator so that location information relating to the user can be
passed between the systems. Finally, the user is given a dual-mode phone
capable of working on the DECT or GSM network. The phone scans for
DECT carriers and, if one is found, registers itself onto the DECT network.
When there is an incoming call it passes first to the DECT system, which
checks to see if the user is registered. If he or she is, then the call is termi-
nated on the DECT network (and hence is carried over the fixed network).
182 The Complete Wireless Communications Professional
If he or she is not, the call is passed to the GSM network for termination
on the mobile network. Outgoing calls are, by preference, made on the
DECT network.
◗Cost: In order to provide the system, DECT base stations must be
installed throughout the place of work. Although not disclosed, it is
thought that the cost of this could be in excess of $1,000 per user
depending on the difficulty in providing coverage in the building.
◗Call billing: Billing for incoming calls is complicated by the fact that
the calling party does not know over what network the call will ter-
minate. As with the personal assistance, typically all incoming calls
are more expensive than normal fixed line calls and, in addition,
the called party may have to pay for incoming calls terminated on
the mobile network.
◗Supplier capability: This can only be provided by a PTO who either
owns a mobile network or has entered into partnership with a
mobile network provider.
◗Revenue potential for operator: By charging a premium for this service,
the operator can achieve increased revenue. It is also thought that
users of such phones would make more calls as a result of the
increased utility that they have from their phone.
◗User needs: The user needs are broadly met by such a service. The
only problem may be that the dual-mode phones are less attractive
than normal mobile phones.
◗Regulatory barriers: The only regulatory barrier is the ability of a
company or the PTO to deploy cordless base stations within their
offices.
Advantages The advantage of this solution is that the user truly has a
single phone on which all his or her calls arrive and from which he or she
makes all calls. The user also gains mobility within the office. For the PTO,
there is the advantage that mobile calls made in the office are routed over
the fixed network and all incoming calls pass to them first.
Disadvantages The key disadvantages are the cost to the corpo-
rate of installing a DECT system and of equipping the users with
dual-mode phones. There is also the potential disadvantage of higher
Interfacing with fixed networks 183
telecommunications cost as a result of having to pay toward the termina-
tion cost of some incoming calls.
6.4.3.4 Mobile substitution—the wireless office
Definition This is similar in concept to the dual-mode phone except
that the coverage in the office is provided by the mobile operator using an
indoor variant of their base stations. Users can then continue to use their
mobile phone wherever they are, with calls being routed to the office base
stations whenever the user is in the office. Compared to the dual-mode
phone, the calling party will typically experience less delay on setup and
the user will have a more seamless offering that allows handover when
leaving the office. The key difference is that in this scenario, the traffic
that was previously carried by the fixed network is “stolen” onto the
mobile network. This solution requires special in-building GSM base sta-
tions and cost-saving solutions such as backhaul compression provided,
for example, as part of the Motorola Wireless Enterprise solution.
◗Cost: The cost is in the provision of the in-building base station. This
cost will typically be borne by the mobile operator rather than the
corporate. There will be little additional cost for handsets, and the
corporate will be able to remove their PBX, resulting in a saving in
this area.
◗Call billing: Call billing is similarly problematic as for the dual-mode
solution because for incoming calls, the calling party has no knowl-
edge of whether they will terminate in the office or on the mobile.
As a result, the called party may have to pay an additional fee to ter-
minate calls when out of the office.
◗Supplier capability: This can be provided by any cellular operator
and, hence, is open to more competition than almost any of the
other option.
◗Revenue potential for operator: This can result in a substantial revenue
increase for the mobile radio operator because (1) they carry addi-
tional call traffic from within the office that should be profitable,
although at a much lower level than normal mobile phone traffic;
(2) they reduce churn in the corporate marketplace because most
offices will only have one in-building system, locking the corporate
in to the operator; (3) in the case where the corporate users were on
a different operator, more valuable corporate users are added to the
184 The Complete Wireless Communications Professional
network who will make additional calls outside the office. For the
fixed operator, the story is completely different as they will lose all,
or most, revenue from this corporate. However, most fixed opera-
tors also have a mobile operation and, by transferring traffic to this
mobile network, can ensure that the traffic is not lost from the
group.
◗User needs: This solution best meets the user needs because the user
truly has one phone with a seamless and consistent service regard-
less of whether he or she is in the office or roaming. The phone can
be more easily personalized, and there is no delay on incoming calls
or problems with redirection.
◗Regulatory barriers: There are no real regulatory barriers, except that
only operators with a cellular license can provide this service.
Advantages This solution is highly advantageous to the mobile opera-
tor who captures more traffic and profit. It is advantageous to the user
who has a truly integrated phone service in that the user only has a single
phone and a single number. Of all the FMC solutions, it probably best
meets the user’s needs, although it is not strictly FMC but substitution
onto the mobile phone.
Disadvantages The key disadvantages are for the fixed line operator
who will lose valuable corporate traffic. Other disadvantages are the need
to provide additional GSM infrastructure within the building. However, it
would appear that this infrastructure soon pays for itself.
Summary A summary of all the different solutions is provided in
Table 6.2.
6.4.4 The future of the FMC
marketplace
The FMC marketplace is currently exhibiting a range of solutions and
opinions as to the most appropriate way ahead. This is partly due to
maturing technology and partly due to the fact that both fixed and mobile
operators are competing for the same (fixed) traffic. Because of this com-
petition, at least two options will remain in place for some time, one, such
Interfacing with fixed networks 185
as BTs OnePhone, put forward by the fixed operator, and the other, such
as Motorola’s Wireless Enterprise, put in place for the mobile operator.
There are also elements in all the solutions that are likely to exist well
into the future. Personal assistants have value even when there is only
one phone by seamlessly handling voice, data, and fax and combining this
with a powerful mailbox capability. Integrated billing and operations
platforms will be appropriate for operators with more than one network
in the same country regardless of whether the users have more than one
phone.
Looking into the future, initiatives such as the universal mobile telecom-
munications service (UMTS) aim to provide one phone for all situations.
Given the benefits of mobility and the advantages of a single phone it
seems likely that FMC in the future will involve some element of mobility
in the office coupled with the use of dual-mode phones if necessary. Both
186 The Complete Wireless Communications Professional
Table 6.2
Summary of the Different FMC Solutions
Degree of
FMC
Fixed
Operator
Advantages
Mobile
Operator
Advantages
User
Advantages Overall
Personal
assistant
Partial,
requires
complex
call
forwarding
Slight
increase in
revenue,
capture some
mobile traffic
None Single
mailbox and
increased
contactability
Acceptable
in the short
term, but not
a long term
solution
Network
integration
Limited,
mainly
billing
Reduces
overall costs
Reduces
overall costs
if part of a
PTO
Limited Does not
provide full
FMC
Dual-mode
phones
Full Retain traffic
that might
have become
mobile
None Single phone
and mobility
in the office
Interesting
solution but
lacking
support
Mobile
substitution
Full None, fixed
operator is
bypassed
(but traffic
may be
carried on
associated
mobile
operator)
Mobile
operator
captures
fixed traffic
and reduces
churn
Single phone
and mobility
in the office
Emerging
solution
likely to be
favored by
many
the dual-mode phone and the wireless enterprise solutions offer the user
similar levels of functionality and can probably be offered for similar lev-
els of cost. These two solutions are likely to play the key role in FMC in the
future, especially in large organizations where wireless PBXs are a practi-
cal proposition. For the SoHo and home worker, solutions might include
the DECT or GSM home base stations or home billing capabilities (the
Home Zone) concept provided by mobile operators.
The FMC marketplace will become a battle of two systems, both
offering the user one phone. The PTO will be keen to use dual-mode
cordless/cellular systems while the cellular operators will be deploying
single-mode wireless enterprise solutions. There is room in the market-
place for both solutions to exist, but at present the wireless enterprise
solution seems more widely supported by the manufacturers and more in
tune with future telecommunications trends. Although both solutions
will probably exist for some time to come, it seems likely to expect that the
wireless enterprise solution will become the eventual answer to FMC,
providing the user with a single phone and a seamless mobility service
wherever they may be.
This brings us back to the quote at the start of this chapter. It may be
that mobile networks coexist with fixed networks at the moment while it
suits them to do so but will increasingly take over the functions of mobile
networks in the future.
References
[]1 Clarke, M., Networks and Telecommunications: Design and Operation, New York:
John Wiley, 1997.
[2] Freeman, R. L., Telecommunications System Engineering: Analogue and Digital
Network Design, New York: John Wiley, 1996.
[3] Griffiths, J., ISDN Explained, New York: John Wiley, 1996.
[4] Wilder, F., A Guide to the TCP/IP Protocol Suite, Norwood, MA: Artech House,
1998.
[5] Clarke, M., ATM Networks and Principles, New York: John Wiley, 1996.
[6] Rahman, M., Guide to ATM Systems and Technology, Norwood, MA: Artech
House, 1998.
Interfacing with fixed networks 187
The mobile network
operator
This part moves away from a consideration
of the underlying technology and looks at
the application of that technology to build
and operate complete radio systems. Design-
ing a network is a complicated task, requiring
an understanding of cell deployment, linking
of cells back into the network, and traffic the-
ory. To get to the stage of building a network
the operator needs to gain a license. The net-
work design and operation is heavily con-
strained by economics, and this part describes
how a business case can be put together and
how the complete wireless professional can
understand financial statements. Operating a
network requires different skills that are also
discussed in this part. Being a network opera-
tor is a skilled task, and one that should not be
undertaken lightly by the complete wireless
professional.
III
PART
Designing a mobile
radio network
Artists can color the sky red because they
know that it is blue. Those of us who aren’t
artists must color things the way they are or
people might think we’re stupid.
Jules Feiffer
7.1 Technical design
7.1.1 Introduction
Most engineers working for mobile radio
operators will at some point be involved in
the network design process. Good design of
the network is essential in order to provide a
high-quality but cost-effective network. This
section looks at some of the major design
issues that encompass all types of mobile and
fixed radio networks.
An overview of the process of setting up
the network is provided in Figure 7.1.
191
Contents
7.1 Technical design
7.2 Applying for a
license
7.3 The mobile
radio equipment
manufacturer
7
CHAPTER
192 The Complete Wireless Communications Professional
Determine
market size,
service area,
and service
offering
Network
planning
Radio
planning
O&M
system
planning
Supplier
selection
Site
acquisition
Site
develop-
ment
Equipment
and facilities
development
System
integration
tests
O&M
system
delivery
O&M
integration
tests
Deployment of network
monitoring tools
Network
operational
Figure 7.1 The network roll-out process.
Each of the key steps in this block diagram are now described, starting
with selecting the number of cells, moving to choosing the cell sites, con-
necting the cells back into the network, and interfacing with switching
and backbone systems.
7.1.2 Network planning
The engineer must not forget that the only purpose of building a mobile
radio network is for the owner of the network to make money. A skillful
network design is one that maximizes the profitability for the owner of
the network. Understanding exactly how to do this requires the engineers
to work in conjunction with the marketing staff over issues such as the
areas for which coverage is required and the features and facilities that are
to be offered. Once these have been decided, the network designer must
try to design a network that achieves these requirements for the lowest
possible cost.
A detailed analysis of almost any sizable mobile radio system shows
that the largest element of the cost is typically related to the number of
base stations, both due to the direct cost of the equipment and the indirect
cost associated with the interconnection of the base stations to the switch
and the site rental charges. Hence, the objective of the engineer should be
to minimize the number of base stations while still meeting the network
coverage and capacity requirements.
To determine the number of cells required in any given area it is nec-
essary to assess how many cells are required for capacity and how many
for coverage and then take the larger of these numbers. Put another way,
there must be at least sufficient cells to provide the required coverage; if
this does not provide sufficient capacity, then more cells will be needed.
The manner in which the number required for coverage and for capacity
are calculated is discussed in more detail, but fundamentally:
◗The number of cells required for coverage is found from the size of
the total area to be covered divided by the area of a cell given the
topographical constraints in that part of the country.
◗The number of cells required for capacity is given by the total
traffic generated divided by the capacity of a cell, where the
total traffic generated is the number of users in the area multiplied
by the traffic generated per user.
Designing a mobile radio network 193
As might be expected, this calculation will differ for different parts of
the country, with city centers presenting a much higher traffic load than
rural areas; hence, the calculation needs to be performed for each part of
the country where these data might differ. The difficulty here is not in
performing the calculation but in obtaining the input information. Topo-
graphic and demographic information is typically readily obtained from
mapping sources or from a census in most developed countries. However,
in developing countries there may be little idea as to the total population,
resulting in the need to use estimates. Determining the expected penetra-
tion is more difficult. By examining other, similar countries, where cellu-
lar is in a more advanced state, it can be possible to make comparisons as
to the expected rise in penetration. Surveys in a range of different areas
can indicate the willingness of the consumers to have mobile radio sys-
tems (although note that survey design is an entire discipline in its own
right, see, e.g., [1]). Traffic levels can be estimated from comparison with
other countries, from looking at the fixed line traffic and fixed line tariffs,
and finally from the survey process. However, it is unlikely that such an
approach would have been able to predict the extremely high penetration
and usage in Hong Kong, due more to social patterns rather than other
indicators, and the engineer must accept that any estimates fed to him by
marketing and research staff are likely to be highly approximate. It is
especially worth remembering the dramatic errors made in the early days
of cellular networks; for example, Vodafone in the United Kingdom pre-
dicted that their TACS network might have a total subscriber base of
100,000 at maturity. It finally peaked at over 2 million.1
The number of cells required for coverage in a particular area is
given by ()
#cells = size of area km2
πrI
2⋅(7.1)
where ris the expected cell radius in kilometers, Iis a factor representing
the inefficiency of tessellating cells due to the need for overlap, and the
symbol # is used as shorthand for “number of.”
The expected radius can be obtained from the base station manufac-
turer or from trial results. For deployment of systems such as GSM, the
194 The Complete Wireless Communications Professional
1. Clearly this was in the early days of cellular, with little experience to go by; predicting
cellular subscriber numbers has become much more accurate. However, for new types of
networks, such as WLL, similar levels of uncertainty might exist.
cell radius in different environments is well known from the large
number of deployments. For newer, or more unusual, deployments a dif-
ferent approach may be required. The basic calculation of cell radius starts
with a link budget of the simplified form indicated in Table 7.1.
The key to the link budget is the receiver sensitivity. This is the signal
level required at the receiver for adequate reception. For example, if an
SNR of 9 dB is required to achieve sufficient voice quality and the noise
floor is −111 dBm, then the minimum signal, or sensitivity, for good
reception is −102 dBm. The sensitivity is typically supplied by manufac-
turers, and minimum acceptable levels can be found in the specifica-
tions.2There is little advantage in having an unbalanced link budget, that
is, having the uplink or the downlink able to tolerate a greater path loss.
When unbalanced it would be possible to reach a situation where the
downlink was of adequate quality and the uplink inadequate. However,
link budgets tend to be slightly unbalanced because the base station has a
directional antenna unlike the mobile and because the base station can
employ lower noise amplifiers that result in a lower noise threshold and
increased sensitivity. In the preceding example there is a 5-dB mismatch
Designing a mobile radio network 195
Table 7.1
A Simplified Link Budget Calculation*
Parameter Downlink Uplink
Transmitter power +43 dBm +30 dBm
Cable and splitter losses −3dB 0dB
Antenna gain +8dB +2dB
TOTAL TRANSMIT POWER +48 dBm +32 dBm
Receiver sensitivity −102 dBm −110 dBm
Receiver antenna gain +2dB +8dB
Cable losses 0 dB −3dB
MINIMUM SIGNAL −104 dBm −115 dBm
MAXIMUM PATH LOSS 152 dB 147 dB
*The increased sensitivity on the uplink compared to the downlink is
a result of better receiver units at the base station than in the mobile
and is also due to the use of diversity reception at the base station.
2. For example, see GSM specification 05.05.
between downlink and uplink. Using the Hata model as an example, the
typical propagation distance associated with this link budget can be
calculated.
The Hata model is an empirically derived model of radio propagation.
It predicts that the signal loss is given by
() ( )
[] []
()
Lfh
ah
dB MHz
cb
m
=+ −
−+−
6955 2616 1382
44 9 655
. . log . log
..lo
[]
[]
()
gloghR
bkm (7.2)
where fcis the carrier frequency (MHz); hbthe base station height (m); hm
the mobile height (m); Rthe distance from BS (km); and a(hm) the mobile
antenna height correction, which differs depending on the environment.
For example, for a medium-sized city
() ()
[]
()
[]
ah f h f
mcmc
=−− −11 0 7 156 08.log . . log . (7.3)
Other mobile antenna height correction elements exist for different types
of terrain. Setting L=147 dB, fc=900 MHz, hb=20m, and hm=2m, the
previous Hata equation can be solved in terms of Rto yield a range of
around 1.5 km.
The number of cells required for capacity is given by
#cells = traffic channels required
traffic channels per cell (7.4)
The number of traffic channels required is given by
()
#channels = E # subs penetration % busy hour Erlangs pe⋅⋅
[]
rsub
(7.5)
where E[x] represents the conversion from Erlangs to traffic channels
using the Erlang formula given in Section 2.3.
7.1.3 Radio planning
It is not sufficient simply to determine how many cells are required;
appropriate cell sites must also be found. If the cell sites are not optimal,
then the coverage from a particular cell may be less than expected or the
196 The Complete Wireless Communications Professional
overlap with a neighboring cell more than expected, resulting in the need
for an increased number of cells. Given a minimum number of cells, the
art of radio planning is to find the cell sites that allow this minimal
number to be realized. There are two key constraints in finding cell sites,
topographical constraint and financial constraints.
◗Topography: In the case where it is desired to maximize coverage it is
important to site cells on high spots since, as shown in Section 7.1.2,
the antenna height has a key bearing on the range achieved. High
sites might either be hills or the tops of tall buildings. However, in
the cases where cells are being installed for capacity and not cover-
age, the converse is true and it is important to limit the range so as to
minimize the interference to neighboring cells. In these cases, it will
be necessary to assess how high a site is required to achieve the
desired cell radius and then to search for a site meeting these
criteria.
◗Financial: In almost all cases the potential sites will be owned by
individuals or corporations who will charge a rental fee for placing
the base station on the land or rooftop space. In some cases, the fee
charged may be unreasonable and it may be less expensive to use a
different cell site that is less optimal but also less expensive.
The problem of siting cells optimally is mathematically intractable
given the complexities of terrain and the difficulties with rental. Instead
of attempting a theoretical solution, the most appropriate way forward is
to make use of a software propagation modeling tool. Such tools take digi-
tal maps of the terrain as inputs and allow the user to place a hypothetical
base station at any point. Using formulas such as the Hata formula, the
model then makes a prediction of the signal strength that would be expe-
rienced. The user can then adjust the position and other parameters of the
base station such as the antenna downtilt until the coverage is as
required. The next base station can then be placed such that the coverage
overlaps to the required degree with the first base station, again using trial
and error until the best position is found. By this method, complete base
station plans can be constructed surprisingly quickly.
Suitable planning tools can be purchased from a number of compa-
nies; for example, MSI in the United Kingdom makes one of the most
widely used planning tools called Planet, while LCC in the United States is
Designing a mobile radio network 197
also a large vendor of planning tools. Most manufacturers also have plan-
ning tools that they can provide to users, although these are often
rebadged versions of tools from companies such as MSI.
Having selected the preferred sites, a site visit is required. This deter-
mines whether it is possible to find space to site the base station and
whether the site owner is agreeable to having the equipment installed. In
many cases there will be problems and it will be necessary to return to the
tool in order to find a different site. In some problematic cases, it may be
that the lack of availability of a site forces a redesign of numerous sur-
rounding sites; hence, it is important that no equipment is actually
installed until all the required sites in an area have been finalized.
7.1.4 Microcells and picocells
The capacity of a cell is independent of its size. Therefore, small cells con-
centrate the same capacity into a smaller area. If a city is covered with
numerous small cells rather than a few large cells the result will be a mas-
sive increase in capacity. Small city cells are referred to as microcells. The
definition of a microcell is that the base station antenna is mounted below
the rooftop level of the surrounding buildings. This results in the signal
being constrained to the streets around the antenna. Typically a microcell
will cover around 200m each side of the transmitter and up to 50m down
side streets that connect onto the main street. A number of software pack-
ages are available to plan microcell networks such as NP Workplace from
Multiple Access Communications in the United Kingdom or modules
available within MSI’s Planet tool. The prediction of microcells is rela-
tively straightforward, the difficulty often resides in obtaining detailed
digital maps of the city showing each of the buildings in the city to an
accuracy of approximately 2m. Over time, such mapping data will
become universally available, possibly through advances in satellite
imagery, but in the short term, planning microcells can be problematic.
In some cases, cells are placed inside buildings. This is typically either
to increase the network capacity by providing yet more cells or to increase
the coverage inside buildings into which the signal is not propagating well
from outside. In-building cells are typically known as picocells due
to their very small size. The size of these cells is constrained very
much by the building. Planning tools exist for picocells from Multiple
Access Communications in the United Kingdom and from a number of
198 The Complete Wireless Communications Professional
manufacturers including Motorola in the United States. These tend to
assume that the signal suffers a loss each time it passes through a wall, a
floor, or a window. The tool needs to know of what each of the walls
within the building are made in order to be able to apply appropriate path
loss criteria. As with microcells, the availability of maps, or in this case
building plans, is the key difficulty. Very few building occupants have
digital plans of their buildings and even fewer know the composition of
the walls and the floors.
To some extent, these problems are being overcome by the increasing
availability of a cheap microcell product that does not require an optimal
placement, since the penalty for using additional microcells to cover
unexpected holes is not severe. Similarly, in buildings, the stage will
eventually be reached where picocells will simply be placed in each corri-
dor and in large rooms and the need for complex planning tools will be
overcome.
7.1.5 Interconnection
One of the key cost elements for the base station is the connection of the
base station back to the BSC and on to the switch. The cost of this connec-
tion will typically be composed of two elements: an initial cost to establish
the connection and an ongoing cost to maintain the connection. The
complete wireless professional must consider the sum of these two costs
in determining the most appropriate means to connect the base station
back to the switch. The most appropriate means to make the connection is
likely to vary in different parts of the country. The key parameters that
have an impact upon the choice of connection method are:
◗The distance between the base station and the base station control-
ler because some interconnection methods have a cost that is rela-
tively distance independent whereas the cost of others is highly
related to distance;
◗The number of carriers deployed at the base station that will affect
the capacity required from the link since some interconnect meth-
ods have a maximum capacity;
◗The presence of available cabling because if there are not copper or
fibber optic cables already in the vicinity, the cost of providing the
cabling will typically be high;
Designing a mobile radio network 199
◗The availability of radio spectrum because without radio spectrum,
techniques based upon radio transmission cannot be adopted.
As with the calculation of the number of base stations required, these
parameters will typically vary from area to area. Often, the highest capac-
ity will be required in city areas, which will be where fiber optic cables are
readily available; whereas low capacities will be required in rural areas,
where cable is not available.
There are two other factors that may impinge upon the selection
of the interconnect method. The first is the desire to use the same type of
interconnect as far as possible throughout the network. This is advanta-
geous in that it reduces the need for staff training in multiple intercon-
nect types, it reduces the need for spares holding, and it simplifies
the operations and maintenance system. Deciding upon whether this
is an appropriate strategy is solely a financial calculation, comparing the
additional cost of using nonoptimal interconnect methods in
some areas with the savings resulting from using a single interconnect
method. As can be appreciated, making this calculation is often diffi-
cult, especially since it is strictly necessary to predict forward to deter-
mine the total number of “inappropriate” links over the lifetime of the
network.
The second factor relates to competitive issues and is even more diffi-
cult to quantify. In some cases, especially for WLL operators, the company
supplying the cabled link, typically the PTO, will be a direct competitor.
The WLL company may have concerns that if they lease a service from the
PTO they may experience poor service on the lines, with higher than
expected outages and higher costs. There will typically be little evidence
that this might be the case and hence little on which to build a financial
analysis of the problem. There may also be the possibility of redress from
the regulator if it is actually found that the service is not meeting the
requirements. Because of these difficulties, such a decision tends to be
more of a “gut feeling” than a financial decision. The complete wireless
professional should try to avoid unquantifiable decisions such as this and
instead seek to demonstrate the cost if the link availability proved poor
and thus be able to determine the break point at which using a different
interconnect methodology would be more appropriate.
The key means of interconnecting the base station sites with the base
station controller use:
200 The Complete Wireless Communications Professional
◗A link leased from the PTO;
◗A microwave point-to-point link;
◗A point-to-multipoint overlay network;
◗A satellite link.
Leased link In this case, the operator obtains a link from another
operator. Often the PTO, but increasingly other companies, such as rail-
way operators, are laying cable that can be used to provide a leased-line
service. The operator specifies the two end points and the data rate to be
provided by the link and the rest is done by the leased-line provider. They
may decide to use satellite or microwave links rather than cable to provide
the link, but this will be invisible to the operator. In return, the operator
pays an annual fee for use of the link. This fee is normally related to the
distance over which the link runs and the capacity required from the link.
There may also be an initial connection fee to link the base station to the
nearest access point in the leased-link network.
In early cellular licenses in some countries, the cellular operators
were required to use the PTO for all their interconnection requirements.
However, this practice is now generally seen as anticompetitive and is
rarely encountered.
Microwave links These are point-to-point radio devices used to pro-
vide a connection that is similar to that provided by a cable [2]. A radio
transmitter and directional antenna are required at each end of the link
with a LOS path between them. Because of their LOS nature, microwave
links are able to operate in higher frequency bands than mobile radio sys-
tems; however, the range does decrease as the frequency increases, as
shown in Figure 7.2.
Designing a mobile radio network 201
0 50 100 150
4
Frequency (GHz)
7.5
13
23
38
58
Distance (km)
Figure 7.2 Microwave link range variation with frequency.
Broadly, a LOS path is required between the transmitter and the
receiver for a microwave link to work; hence, most links tend to be com-
posed of transmitters and receivers on tall masts or in elevated locations.
Microwave links differ in their coding and modulation scheme from
mobile radio systems. Typically, because of their directionality, micro-
wave links generate little cochannel interference to other microwave
links and, hence, high SNR and SIR values can be achieved. As a result,
fixed links tend to use high-level modulation schemes such as 64-level
QAM, linked with trellis code modulation [3]. Links are typically pro-
vided with “standard” data rates ranging from 2 to 34 to 155 Mbps.
The cost of a fixed link is the equipment and masts required. Hence, as
long as the required link distance does not exceed the range of the equip-
ment, the cost is unrelated to distance. Although higher capacity link
equipment is more expensive, the difference compared to a lower capac-
ity link is relatively small, so link cost is only slightly related to link dis-
tance. A comparison of the through life cost of a 2-Mbps fixed link with a
leased line is provided in Figure 7.3. This figure will vary from country to
country depending on the cost of the leased line charged by the PTO and
on the availability of spectrum for fixed links.
Point-to-multipoint overlay networks This is a relatively new con-
cept that is undergoing trials at the moment. It is similar to the point-to-
point microwave links except that, instead of having a separate dish at the
base station controller for each base station, a single antenna is used to
gather all the signals (in the same manner that a single antenna is used
at a cellular base station to gather the signals from all the subscribers).
If fact, such an overlay network is a form of WLL system, since each of
the base stations looks like a fixed subscriber. Such systems are less
202 The Complete Wireless Communications Professional
0
50,000
100,000
150,000
200,000
250,000
Distance (km)
Fixed link
Leased line
Throughout life cost ($)
5 101520253035404550
Figure 7.3 Fixed link versus leased line costs for a 2-Mbps link.
expensive than point-to-point systems since dedicated antennas and cir-
cuitry are not required for each link at the base station controller. How-
ever, they typically have a lower range both as a result of not using a
directional antenna at the base station controller and because the system
capacity may not be as high. This low cost but low range makes them par-
ticularly suitable for providing backhaul for microcells within a city area,
and indeed some of the first applications suggested were for the backhaul
of cordless base stations. The WLL system needs to provide a high capacity
per base station with systems such as Ericsson’s AirLine (see Section 5.3)
with its 2 Mbps per user being appropriate. These are termed overlay net-
works because they can be considered to be radio systems sitting on top of
other radio systems or overlaying them. It is likely that an increasing
number of these sorts of systems will be deployed in the future, both as
the technology becomes less expensive and as the number of microcells
and picocells increases.
Satellite links If the distance from the base station to the switch is
greater than around 100 km and there is no existing infrastructure, then
satellite systems may be the most appropriate means to provide the link.
Satellite systems have the advantage that they are truly distance inde-
pendent and can operate immediately in most parts of the world. Using
VSATs, data rates of up to 2 Mbps can be provided. Even in the case that
distance is not a problem, satellite systems are sometimes deployed. Dur-
ing the roll-out of the U.K. National Lottery, BT was unable to respond
sufficiently rapidly to provide leased lines into each of the shops selling
tickets and so around 2,000 were connected using satellite links. How-
ever, in this case, the cost was relatively low since the amount of data
being transferred from each terminal was only a few tens of bits per
second.
Satellite systems have the disadvantage of adding an extra delay to
the signal and of a relatively high cost if significant bandwidth is required.
For example, the cost of renting a 2-Mbps leased line is approximately
$500,000 per year, which is normally much more expensive than the
other options described previously.
7.1.6 Operations and maintenance
planning
The operations and maintenance (O&M) system typically requires little in
the way of planning. It will be necessary to understand the size of the
Designing a mobile radio network 203
network in terms of number of cells in order to be able to order an O&M
with adequate capacity. Another important point will be to determine
how many network control rooms are required, whether they will be
located close together, and whether some will be shut down during off-
peak periods in order to reduce staffing numbers. It might also be neces-
sary to consider future network upgrade plans, such as a plan to add
packet data transmission at a later date. Clearly, it will need to be possible
to reconfigure the O&M system in order to add the capabilities.
7.1.7 Supplier selection
Supplier selection is a time-consuming and complex area that covers both
technical and financial matters. A textbook supplier selection process
would cover the following stages.
1. Detailed understanding of the requirements of the equipment
based upon preliminary network design, prediction of future
requirements, and an understanding of all the services that are to
be offered.
2. Development of a request for quotations (RFQ), which is a formal
document setting out the requirements on the equipment. Each
requirement is listed, along with an indication of whether it is
mandatory or optional. The writing of such a document is highly
time consuming because it must cover everything from lightning
protection and earthing requirements, to equipment size, to all
aspects of equipment function.
3. The RFQ is sent to a short list of preferred suppliers.
4. The quotations received from the suppliers are formally evalu-
ated. Each quotation may be scored against the number of
requirements that it is able to meet. Then there follows the
difficult process of comparing the prices offered against the func-
tionality “score.” Often the highest functionality will have the
highest price associated with it.
5. Contract negotiations commence with the preferred supplier.
6. Once the contract has been signed, the equipment manufacture
and delivery can commence.
204 The Complete Wireless Communications Professional
It is often tempting to shorten these procedures, especially when pro-
curing commodity items such as GSM base stations. Less formal systems
can save substantial amounts of time but can lead to problems at a later
stage. Many operators make use of consultants during the supplier selec-
tion process in order to provide the necessary man-power and expertise.
Selecting a consultant who already has a template RFQ can save substan-
tial time and effort.
7.1.8 Network deployment
The deployment of a cellular network, once the sites have been selected
and the equipment has been procured, is essentially a large-scale project
management task. The operator might be rolling out one site a day in
order to meet coverage requirements. Each site requires a survey, civil
works to erect the mast, the provision of power and communications, the
delivery of the base station to the site, the erection of the mast, the instal-
lation of the antennas, and the commissioning of the base station. This
will require a wide range of contractors from civil engineers to antenna
riggers. Ensuring that each person turns up to the site when required is a
major logistics exercise. Increasingly cellular operators have been turning
to large civil engineering companies to provide the project management
skills required for such a venture. Such companies will have project man-
agement experts, a range of project planning tools, and the required
experience. The difficulties of network deployment should not be under-
estimated, but this is a task that the complete wireless professional can
delegate to those with more appropriate skills, only becoming involved
during commissioning and test and when unexpected problems arise.
7.2 Applying for a license
A license application is generally required before an operator is provided
with radio spectrum and a license to run a telecommunication service.
General factors to include within the license application are:
◗Introduction;
◗Overview of the operator including ownership and turnover;
◗Details of the service proposed;
Designing a mobile radio network 205
◗A technical description of how the network will be realized;
◗A marketing plan showing the services that will be offered and any
new and innovative means for provision of the mobile radio service
(e.g., the use of prepayment mechanisms);
◗A demonstration that the radio spectrum required is being used
efficiently;
◗Simplified business plans showing the justification for building the
network;
◗A network build plan showing the speed with which the network
will be built;
◗A summary of the advantages to the country;
◗Appendixes including coverage maps, detailed technical informa-
tion, details of the frequencies required, and interference assess-
ments with other users of the radio spectrum where required.
The most important fact to understand is what the regulator or gov-
ernment wishes to get from the license award. Possible government
objectives will include:
◗Increasing the competition for telephony in the country;
◗Increasing the wealth of the country through enhanced provision
of communications;
◗Providing telephony to rural regions;
◗Stimulating local industry and improving local skills;
◗Gaining a cash injection through the sale of radio spectrum;
◗Providing higher bandwidth services, allowing further economic
development.
It is a little realized fact that the best license applications are often pro-
duced by small operators with apparently limited resources while the
worst license applications are often produced by the large multinational
partnerships who, it would seem, should have both more experience and
greater resource than the smaller companies. There are many reasons for
206 The Complete Wireless Communications Professional
this, but key is the quality and number of staff responsible for writing the
bid. In the same manner that books written by one or two authors typi-
cally have more continuity than edited books where each author has
written a different chapter, license applications written by small closely
knit teams are typically better than those written by very large teams from
a range of different organizations with different cultures and values. The
large companies also are often rather arrogant about their power and per-
haps do not assign the quality of staff required to the process. The best
way to write a license application seems to be to assemble a small team of
half a dozen highly skilled individuals, experts in their own fields and
with good writing skills, and to provide them with whatever support they
desire (such as technical staff to produce some coverage plans).
A good license application should read like a good book, with clear
logical flow and lack of repetition. It should avoid providing information
well-known to the assessors, like the architecture of the GSM system, and
concentrate on describing the novel and advanced features that will be
offered in the network. A common trait in license applications is to start
sections with “Company x will provide a network of the highest quality
with exceptional coverage and capacity,” but then not to substantiate this
statement in any way. A good license application would then go on to
explain how microcells will be widely deployed, showing that the cost
and coverage area of a microcell was fully understood, then developing
some traffic models, and showing how the network capacity would be
well in excess of these traffic models.
It is becoming increasingly true that licenses are won not on technical
capability but on the new services that will be offered by the network
and on the new means of marketing and providing good customer
support. Most assessors now assume that any large organization can
muster the technical skill to assemble what is becoming a commodity—a
GSM network. Licenses have been won based on a commitment in
the license application to reimburse customers for any calls that were
dropped—something that requires little technical skill but an under-
standing of the cost of such a commitment. The importance of engineers
in writing the license application is therefore diminishing for all but the
new and unusual networks (such as WLL deployments or dual-mode
systems). Engineers should realize this and ensure that they have all
the marketing and sales support that is required.
Designing a mobile radio network 207
7.3 The mobile radio
equipment manufacturer
Many engineers will work for manufacturers rather than operators in a
range of roles including equipment design and manufacturers, research
and development, antenna design, test equipment design, software tools
for mobile radio system, and RF component design, for example. The
basic role of the manufacturer is to provide the equipment required by the
operator for them to provide a profitable service. However, this is far from
simple as the operators often do not know exactly what they want nor
what is possible. Design cycles are often four years or more long; hence,
the manufacturer will need to develop products well before they are
required by the operators. This is evidenced in standards forum where the
vast majority of contributors are the manufacturers. The only operators to
attend are typically those that are also PTOs and have a large research
facility.
In a world that is increasingly dominated by standards, the manufac-
turer will seek to work in the following manner. First, they will conduct
research around the areas on which standardization is required and will
seek patents on any key breakthroughs. They will then try to drive the
standard in the direction of their patent so that they hold as much of the
key IPR as possible around the standard. This ensures that they will not
have problems with other manufacturers charging high levels of payment
to use their patents and raises the potential that the first manufacturer
will themselves be able to benefit from royalty payments. For these rea-
sons, the standards forums can become quite heated, as explained in
more detail in Chapter 13.
Once the standard has been completed, the manufacturer will work
as quickly as possible to bring the product to market. They will also be
looking for ways to differentiate their product from the competitors while
still conforming to the standard. In the area of handsets, this might be by
making them smaller, with longer battery life than the competitors. In
the case of the network, this might involve lower power consumption,
greater sensitivity, and requirements for less communication resources,
for example. In the world of GSM infrastructure there are hundreds of
ways in which products from different manufacturers are differentiated.
208 The Complete Wireless Communications Professional
Manufacturers will also seek to prime markets. A good example of
this is in the area of in-building coverage. This is an area that the manu-
facturers would very much like to develop since it would allow them to
sell increased volumes of infrastructure for installation in office buildings
around the world. The manufacturers cannot sell this product until the
operators are convinced of its benefits. Hence, the manufacturers need
to perform the business case and the trials in order to demonstrate
the viability to the operators. Once the market has been “seeded,” the
manufacturer can take a less dominant role since the “pull” from the
operator will become sufficient to develop and sell product.
Some manufacturers are increasingly taking on a role as operators. In
most cases, this is somewhat unwillingly because historically manufac-
turers have tended not to be successful as operators due to the different
skills required. However, today’s operators are expecting vendor financ-
ing (see Section 8.2.5) and for the manufacturer to build, operate, and
transfer (BOT) the network to them. The result is the manufacturer per-
forming the network design and initial network operation and maintain-
ing a position on the board of the operator so that they can see that their
investment is being safeguarded. It is not clear where this trend will lead
in the future, and indeed it may be unhealthy for competitive supply if
manufacturers take too large a stake in operators.
Manufacturers are starting to see the cellular marketplace changing.
Until recently, cellular remained a complicated and knowledge-intensive
industry where only those manufacturers with background expertise in
communications and an excellent research and development capability
could flourish. These manufacturers were able to charge a premium price
as a result of their expertise. Now, with the increasingly widespread avail-
ability of chipsets for most of the major wireless standards, it is compara-
tively simple to become an equipment provider and many electronics
companies are entering this field. Just like radios and televisions, cellular
is now becoming a commodity product with the effect that manufacturers
are continually reducing prices. The manufacturers are trying to differen-
tiate themselves by having better specifications or wider features lists and
by opening new markets such as WLL and in-building where their supe-
rior technical expertise will allow them to charge higher prices in the
short to medium term.
Designing a mobile radio network 209
References
[1] Crimp, M., The Market Research Process, New York: Prentice-Hall, 1990.
[2] Freeman, R., Radio System Design for Telecommunications (1-100GHz), New York:
John Wiley, 1987.
[3] Webb, W., and L. Hanzo, Modern Quadrature Amplitude Modulation, New York:
John Wiley, 1994.
210 The Complete Wireless Communications Professional
Economics of a
mobile radio
network
Money is what you’d get on beautifully
without, if only other people weren’t so
crazy about it.
Margaret Case Harriman
8.1 Understanding financial
information
8.1.1 Introduction to accounting
Engineers typically do not find accounting
interesting. Compared to the ability to design
a network and see something realized and
working, the compilation of numbers in a
strict and unbending format has little allure.
This is not unduly problematic as engineers
will rarely be asked to write the accounts.
However, engineers are often asked to look at
the accounts and to contribute information
to the business planning process. When the
211
Contents
8.1 Understanding
financial information
8.2 The business case
8
CHAPTER
business plan does not show an adequate return on investment, the engi-
neer may be expected to find savings in the network design. An under-
standing of how to read and analyze conventional ways for representing
monetary flows is an important attribute for the complete wireless profes-
sional. There are many books that can be used to provide a guide to the
manner in which accounts are compiled; however, the wireless profes-
sional has no need for those that tell the reader how to actually perform
the accounting process. Some useful reference works for those looking to
delve deeper into the accounting process include [1–3]. In this section, a
simple guide is provided to the three main parts of the accounts: the profit
and loss statement, the balance sheet, and the funds flow statement.
It is important for the complete wireless professional to understand
the standard accounting format used around the world and the means
whereby a business plan is put together.
8.1.2 The profit and loss account
The prediction of the profit and loss account for a network lists the
incomes and expenditures for a business for each year of operation. The
company accounts will show the profit and loss account for the year just
past. It shows how much profit has been made and how that profit is
used—whether paid out to the shareholders or retained for future use.
The profit and loss account basically adds up all the income and then sub-
tracts from that all the costs. A fabricated (but nevertheless approximately
accurate) profit and loss account for a cellular operator projected for the
first eight years of operation is shown in Table 8.1.
Most of this is relatively self-explanatory. Income is made up of con-
nection and subscription fees and call usage fees. It also arises from call
fees paid by roaming subscribers and interconnect revenue (explained in
more detail in Section 8.2.4) that is paid to the cellular operator when an
incoming call is terminated on a mobile phone. Against this is balanced
the costs of providing this service mainly related to the handset subsidy
and the cost of acquiring subscribers. There is also an interconnect cost
associated with calls that are terminated on other networks. Note at this
point that nothing has been said about the cost of providing the network
itself. The difference between the income and the costs directly associated
with that income is called the net revenue.
212 The Complete Wireless Communications Professional
Economics of a mobile radio network 213
Table 8.1
A Typical Profit and Loss Account
1998 1999 2000 2001 2002 2003 2004 2005
Revenue All in US$ million/year
Connections 0.3 0.9 0.8 1.0 0.9 0.6 0.4 0.2
Subscriptions 2.2 6.9 10.8 16.0 20.6 24.0 26.9 29.0
Call usage 3.4 12.7 22.4 30.6 38.1 43.4 46.5 47.3
Roaming fees 0.8 1.0 1.3 1.6 1.9 2.1 2.4 2.5
GSM services 7 22 35 49 62 70 76 79
Interconnect revenue 0.7 2.7 4.9 6.9 8.9 10.5 11.9 12.5
Total gross revenue 7 24 40 56 70 81 88 92
Direct costs
Handset subsidy 1.0 2.5 2.2 2.4 1.7 0.9 0.2 0.2
Sales costs 0.2 0.7 1.2 1.7 2.4 4.7 5.1 5.3
Interconnect costs 0.1 0.5 0.9 1.4 2.0 2.5 3.0 3.5
Total direct costs 1 4466889
Net revenue 6 21 36 51 64 73 80 83
Operating expenses
Maintenance 1.7 1.9 2.2 2.5 2.8 3.1 3.3 3.4
Leased lines 0.0 0.0 0.0 0.1 0.1 0.1 0.1 0.1
Sales and marketing 1.2 3.3 3.0 3.5 3.6 3.1 3.2 2.7
Staff 1.6 4.1 2.5 2.9 3.0 3.4 3.6 13.2
Accommodation 0.2 0.3 0.4 0.5 0.6 0.8 0.9 1.6
General and
administrative
0.9 1.2 1.7 2.2 2.8 3.3 3.7 4.2
Consultancy 0.6 ———————
Regulatory fees 3.9 1.8 1.8 1.8 1.8 1.8 1.9 1.9
Bad debts 0.0 0.1 0.2 0.3 0.4 0.4 0.5 0.5
Contingency 0.3 0.4 0.4 0.4 0.5 0.5 0.5 0.8
Total operating
expenses
10 13 12 14 16 16 18 29
Operating profit (4) 7 24 36 49 56 62 54
Less: Depreciation (4 10111314151617
Net profit before
interest and tax
(9) (2) 12 24 34 41 46 37
The indirect or operating expenses such as the costs of leased lines and
office space are offset next. The net revenue less the total operating
expenses forms the first of a number of definitions of profit (so if someone
just quotes a profit, be clear to which part of the profit and loss account it
refers). This profit is called the operating profit and determines whether a
profit is made when the income is compared to the direct and indirect
costs of providing that income.
The next step is to subtract depreciation. Depreciation is a slightly
confusing accounting convention and is worth explaining in more detail.
Imagine a generally profitable company that decides one year to replace
its main building. If the cost of the building was placed directly on the
profit and loss statement, the company would show a loss for that year,
despite the fact that the business was profitable and the building would
contribute to profits over the coming years. Investors might lose faith in
the company unless it was explained to them that the company was still
profitable but just had a large piece of expenditure. The argument would
then be that if the company is profitable why does the profit and loss
account not show a profit? The convention of depreciation is a way
around this problem. Instead of placing the whole of the cost of the build-
ing in the year it was built, the cost is spread across the expected lifetime of
the building, normally in a linear fashion (exponential or quadratic
depreciation is sometimes used, but normally judged to be too complex).
Because judgments about the lifetime of certain items, coupled with pos-
sible resale value, become complex and open to “creative accounting,”
there are a number of rules that determine how depreciation should be
approached.
214 The Complete Wireless Communications Professional
Table 8.1 (continued)
1998 1999 2000 2001 2002 2003 2004 2005
All in US$ million/year
Interest payments
(receipts)
(3 3332 (1)
Tax 5 8 11 14 16 14
Net profit after
interest and tax
(9)(5) 41220263024
Less dividends 5 17 14 15
Retained earnings (9) (5) 4 12 15 8 16 9
There are plenty of misconceptions surrounding depreciation. The
fact that an object is depreciated does not mean that any money has been
saved for a replacement. If an object has been fully depreciated and is still
in use, it does not mean that it should be disposed of, just that the original
estimate of its lifetime was incorrect. In fact, a fully depreciated item is no
different than a partly depreciated one, except in the manner it is repre-
sented in the profit and loss statement. Sometimes depreciated items are
disposed of before they have lost all their usefulness purely for tax pur-
poses so that a new item can be brought, the depreciation on the profit
and loss account increased, the profit decreased, and hence the tax liabil-
ity reduced. This need not concern the complete wireless professional,
only the accountant.
As can be imagined, depreciation is an important issue for the mobile
radio operator who has to buy and install a high-cost network in the early
years of operation. Typically, the cost of this network is depreciated over
10 or 15 years, resulting in a relatively small entry in the profit and loss
account in the early years (10% of the actual expenditure during the year
in this example). Because of depreciation, the profit and loss account does
not reflect whether there is money in the bank (because a profit after
depreciation would not necessarily be a profit after the full expenditure is
taken into account) and, hence, the profit and loss account cannot be
used to estimate the funding requirement.
After the depreciation has been subtracted from the operating profit,
what remains is the net profit before interest and tax. This is sometimes
abbreviated earnings before interest and taxation (EBIT). Subtraction of the
interest and the tax payable results in the profit after interest and taxa-
tion. The company then makes a decision as to what it is going to do with
this profit (or loss), typically either pay it to the shareholders or retain it
for future purposes.
8.1.3 The balance sheet
The balance sheet is of less interest to the wireless professional than the
profit and loss account. The balance sheet shows what the company owns
and how it is financed. It is useful in determining the value of the com-
pany and checking on how much money it owes. It is of no use in deter-
mining whether the operation is profitable and little use in determining
whether a business plan is appropriate—the profit and loss account is best
Economics of a mobile radio network 215
suited to this purpose. A balance sheet for the same cellular operator is
shown in Table 8.2.
The balance sheet seeks to assess everything the company owns.
Clearly it owns infrastructure such as base stations and towers, which are
known as fixed assets (because they are fixed in space and difficult to sell
quickly). Each year more fixed assets are added but against this, the
existing fixed assets lose value as they become older and this loss of value
is calculated by subtracting the depreciation from the total value of
the network. This results in the sum of fixed assets less accumulated
depreciation.
Below this comes current assets. These are short-term resources that
are either cash or expected to become cash in the next year and they typi-
cally comprise stocks (work in progress), debtors, and cash. In the case of
a cellular operator there is little in the way of stock. Debtors represent
unpaid bills at the end of the year (typically the bills from the last month
of operation before the date of the balance sheet), and then cash is split
between cash in the bank and cash held in short-term deposits (where it
can earn a higher rate of interest).
It is then necessary to subtract from this the liabilities: money or goods
owed by the company. In this case, the operator owes its creditors money
216 The Complete Wireless Communications Professional
Table 8.2
A Typical Balance Sheet
1998 1999 2000 2001 2002 2003 2004 2005
Fixed assets All in US$ million/year
Fixed assets at year start — 85 99 113 127 144 155 166
Additions: Network 84.2 13.2 14.5 14.0 16.1 10.5 10.9 8.2
Towers 1.0 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Office
equipment
0.2 0.0 0.0 0.0 0.0 0.2 0.0 0.0
Total
additions
85 13 15 14 16 11 11 8
Total fixed assets at cost 85 99 113 127 144 155 166 174
Less: Cumulated
depreciation
414 2538526884101
Fixed assets less
accumulated depreciation
81 85 88 89 91 87 81 72
(typically delayed payments to providers of equipment) and payments
promised to shareholders which have not yet been paid. The total of cur-
rent assets minus current liabilities forms the net current assets and,
Economics of a mobile radio network 217
Table 8.2 (continued)
1998 1999 2000 2001 2002 2003 2004 2005
Current assets All in US$ million/year
Stocks ————————
Debtors 0.4 1.6 2.8 3.8 4.8 5.4 5.8 5.9
Cash at bank 1.7 2.2 2.0 2.4 2.6 2.7 2.9 4.8
Short-term
deposits
——————18.0 36.0
Total current
assets
24 56782747
Current liabilities
Creditors 12 3 3 3 3 3 3 3
Dividends
payable
———— 51714 15
Total current
liabilities
12 3 3 392017 18
NET CURRENT ASSETS (9) 1 2 3 (1) (12) 10 28
TOTAL ASSETS 72 86 90 93 90 75 91 101
Financed by:
Bank loans 40 50 50 41 23 — — —
Owner’s equity
Shareholders
capital
40 50 50 50 50 50 50 50
Reserves — — 0 1 2 3 5 6
Retained
earnings
—−9−14 −10 11522 37
Profit (loss)
current
period
−9−54 11 14 7 15 8
Total
owner’s
equity
32 36 40 52 67 75 91 101
TOTAL CAPITAL AND
RESERVES
72 86 90 93 90 75 91 101
when this is added to the fixed assets, provides the total assets of the com-
pany. This is one-half of the balance sheet.
The second half shows where the money has come from to pay for
these assets. This is divided into loans (bank loans) and then the money
that the owners have put into the business, mainly from payments by
shareholders purchasing shares. In addition, there is money transferred
to reserves, earnings retained from previous years, and the profit from the
current year that can all be used to finance the costs of the network. The
net current assets should equal the total capital and reserves, hence the
balance sheet is said to balance. If it does not, then there are either some
assets that apparently do not belong to anyone or some additional financ-
ing that has apparently been lost.
8.1.4 The funds flow statement
The funds flow statement is rendered necessary by using depreciation in
the profit and loss account. As a result, the profit and loss account does not
show how much money is flowing in or out of the bank at any time. The
funds flow statement does just this—it shows where money is flowing in
and out and hence allows the maximum funding requirements to be
determined so that suitable financing can be agreed with banks or what-
ever. The engineer will have very little concern with the funds flow unless
there is a maximum funding requirement that needs to be met. An exam-
ple of a funds flow statement for the same mobile radio operator is shown
in Table 8.3.
The way that this is calculated is moderately interesting. The cash
inflows are profit (from the profit and loss account) plus depreciation
(since this is never “paid” in any case) plus any interest. The outflows are
the capital expenditure, interest payable, any change in working capital
(money held in the bank to pay items such as salaries), and tax payable.
The difference between these two shows whether additional cash is
required on an annual basis. As can be seen, after the third year, the busi-
ness starts to generate more cash than it consumes (becomes “cash posi-
tive”). Clearly, the requirement for cash needs to be met. In this case, the
funding comes from the shareholders and from the bank; this part of the
funds flow shows the additional funding required each year, with half
coming from the shareholders and half from the bank.
218 The Complete Wireless Communications Professional
Economics of a mobile radio network 219
Table 8.3
A Typical Funds Flow Statement
1998 1999 2000 2001 2002 2003 2004 2005
Cash inflows All in US$ million/year
Profit before
interest and
tax
−9−212 24 34 41 46 37
Plus
depreciation
410111314151617
Interest
receipts
——————— 1
Total cash
inflows
−47243649566255
Cash outflows
Capital
expenditure
85 13 15 14 16 11 11 8
Interest
payments
— 33332——
Working
capital
increase/
(decrease)
−910111101
Corporation
tax
— — 5 8 11 14 16 14
Total cash
outflows
76 27 24 27 31 27 27 23
CASH SURPLUS/
(FINANCING REQUIRED)
−80 −19 −1917293532
Funded by:
Shareholders
equity
40100—————
Shareholders
advances
————————
Bank loans 40 10 0 —————
Short-term
deposits
————————
Total annual
funding
80191—————
Once there is a cash surplus, it is important to understand for what it is
used. In this case it is used first to pay back the bank loans and is then paid
as dividends to shareholders, with some additional cash used for short-
term deposits. Only by the eighth year are all the debts paid and the com-
pany actually has cash in the bank. The final section shows the cumula-
tive bank loans required, where it can be seen that loans of up to $100M
in the third year will be required, with all bank loans being paid back by
the sixth year. Clearly, the bank will be very keen to examine the funds
flow statement.
220 The Complete Wireless Communications Professional
Table 8.3 (continued)
1998 1999 2000 2001 2002 2003 2004 2005
All in US$ million/year
Used for:
Repayment
of bank loans
——— 91723——
Surplus distributed as:
Dividends ————— 51714
Transfer to
short-term
deposits
——————1818
Total — — — 9 17 29 35 32
CUMULATIVE CASH
SURPLUS/FINANCING
REQUIRED
−80 −99 −100 −91 −73 −45 −922
Cumulative funding
Shareholder
funding
40 50 50 50 50 50 50 50
Shareholders
advances
————————
Bank loans 40 50 50 41 23 — — —
Total
cumulative
funding
80 99 100 91 73 50 50 50
CUMULATIVE CASH
RESERVES
——————1836
8.1.5 Performing first pass modeling
Although wireless professionals are rarely asked to build complete finan-
cial statements, they may be asked to perform some first pass modeling in
order to assess the practicality of certain situations. This section describes
how this is done using a real-life example (although all of the specific
details have been changed to preserve commercial confidentiality). The
key is both in knowing how to provide the resulting information and in
understanding when assumptions can be made and when sensitivity
analysis is required. The example is based on the introduction of a railway
GSM service into a public GSM network; for more details on the railway
GSM service, see Section 10.2.
At the highest level, this sort of analysis compares the inflows with
the outflows over a period of time and determines whether the operation
will be profitable. In the case of this example, the outflows are relatively
clear; the network must be enhanced to provide the services needed by
the railways. Discussion with the railways showed that the following
changes to the network would be required.
◗Coverage would be required along some railway lines that would
not previously have been covered.
◗The additional features of group and broadcast call and packet data
provision would need to be added to all base stations covering the
railway lines.
◗Base stations covering the railway lines would need to be made
more reliable through the provision of a standby transmitter that
could be switched on should the main transmitter fail.
Determining the cost of all these additions was not straightforward. In
determining the cost of additional coverage, the number of additional
base stations needed should have been calculated. However, in a first pass
assessment of this sort there typically is not the available resource to per-
form cell planning along the railways. Instead, an estimate was made as to
the coverage radius of a typical railway cell and then the length of track to
be covered was be divided by the cell size (twice the radius) to arrive at an
estimate of the number of cells. When attempting to cost the additional
features there was the difficulty that manufacturers were still developing
Economics of a mobile radio network 221
the features and, therefore, unable to provide an estimate of their addi-
tional cost. The best approximation was to look at the additional cost of
features that seemed to be of a similar complexity and had already been
provided by the manufacturers. Fortunately, the cost of a standby trans-
mitter could be accurately determined.
Next, the timescales over which these new features are to be deployed
were determined, and as a first pass the cost of the new features was
spread linearly across this timespan. When calculating the cost it was nec-
essary to include the cost of maintenance in terms of engineering staff and
spare parts, the cost of transmission from the base stations, and the cost of
site rental and power. The last three form ongoing costs that would last for
the lifetime of the project.
Having determined the costs, the revenues could be calculated. How-
ever, at this stage, the price to be charged to the railways was not known
and would remain a subject for negotiation for some time. The first pass
analysis looked at the feasibility of the project by asking “if the railways
continued to pay the same levels as they currently do for their existing
network, would the GSM network be profitable?” Existing costs could
sometimes be obtained from the railways; if not, estimates were made
based on the number of base stations and the equipment deployed. The
current payment was then compared with the GSM costs to determine
whether it was worth proceeding further with the negotiations and, if so,
what the lowest acceptable payment from the railways would be.
When evaluating the overall monetary flows it is important to look at
the NPV of the project (NPV is discussed in Section 8.2.6). This allows
appropriate compensation for the cost of capital and the likelihood that
the operator will need to invest money in the first place before that cost
can be recouped through annual payments from the railways. Having
performed this analysis, it is instructive to examine how sensitive the
results are to the assumptions made. For example, the cost of the
enhancements and the number of base stations required were both esti-
mated. By changing these figures by, say, ±10 and ±20%, the impact on
the payments required from the railways can be seen. If there is a signifi-
cant sensitivity to this variable, then it would be appropriate to investigate
the likely value of the variable in more detail by, for example, performing
some modeling of coverage along the additional railway lines.
222 The Complete Wireless Communications Professional
8.2 The business case
8.2.1 The overall structure of the
business case
The business case is typically a spreadsheet model that shows how the
money to be invested in building a telecommunications network will be
repaid. The business case reveals whether an attractive rate of return can
be earned on the capital and, as a result, whether the project should be
undertaken. The business case is effectively the profit and loss projection
as described in Section 8.1; here, we look at the way that the constituent
parts of that projection are developed.
Broadly, the business case subtracts total expenditure in the form
of capital and operating expenses from the total revenue derived from
the subscribers. The difficulty lies not in performing the mathemat-
ics but in deriving accurate estimates of expenditure and revenue. In
particular, it is in the area of expenditure where the greatest difficulty
lies. Estimating subscriber revenue is not something covered in detail
in this book—it belongs more to the area of forecasting and market
research—but fundamentally, predictions must be made about subscriber
numbers based upon historical growth for other operators, penetration
levels, analysts’ predictions as to future subscriber numbers, and an
understanding of demographic, social, and technical trends.
8.2.2 The network costs
One of the key cost components is the capital cost associated with the pur-
chase of the network. Similar to network equipment, most cellular opera-
tors now purchase the mobile phones and subsidize their sale to the
public. Hence, it is necessary to consider the sum of both the infrastruc-
ture and the subscriber unit costs.
Subscriber unit costs The basic cost equation here is to multiply the
difference between the manufacturer’s price and the subsidized price by
the volume of units sold. This can be complicated by the fact that there is
typically a wide range of mobiles, each mobile attracting a different
amount of subsidy. The key elements of the equation are:
Economics of a mobile radio network 223
◗The number of mobiles subsidized each year: This will equal the pre-
dicted gross number of new subscribers each year and the extent to
which mobiles are subsidized. (Gross subscriber numbers are the total
number of new subscribers joining the network in the year. Net sub-
scriber numbers are equal to the gross numbers minus the number of
subscribers leaving the network.) In some countries no subsidy is
paid and the user must pay for the handset in full. In other countries
a full subsidy is provided and the user gets the handset for free. It is
in the subsidy that the impact of “churn” (i.e., users leaving one
network to join a different network) is felt.
◗The projected cost of the units over the investment period: In most cases,
mobile costs fall as manufacturers move along the learning curve.
Estimating future falls is difficult and manufacturers will be unwill-
ing to commit to aggressive cost reductions. Historical trends can be
useful and they typically show steep price falls when a new technol-
ogy is introduced, with price levels falling increasingly slowly as the
technology becomes mature.
◗The sales cost: This cost is composed of the advertising and distribu-
tion costs of signing new subscribers. This cost includes the costs of
the shops used to sell subscriptions and the time of the sales staff in
these shops.
A typical spreadsheet for the calculation of the mobile subsidy cost
might look like Table 8.4.
The length of time over which the investments will be considered is
not always obvious. Typically, large infrastructure projects (which a tele-
communications network is) are considered over the lifetime of the infra-
structure. Although a telecommunications network will probably last for
around 15 years, advances in technology might make it redundant long
before that. As a result, some investors only look over a 5-year horizon.
However, as mobile communications becomes more competitive, returns
in less than 5 years are increasingly rare and a compromise of a 10-year
investment window is often used. A 5-year cycle has been shown here to
allow the tables to fit easily onto the page and not to complicate the
analysis.
224 The Complete Wireless Communications Professional
Network costs The network costs are comprised of:
1. Base stations;
2. Base station interconnection;
3. Base station controllers (if required);
4. Base station controller interconnection (if required);
5. Switching costs;
6. Operations, maintenance, and billing system costs.
For each of the capital items (i.e., items 1, 3, 5, and 6) there will be
hardware costs, installation costs, and planning costs.
◗The hardware cost will be provided by the manufacturer. It is often
important to take account of all the cards needed to fully populate
the equipment racks when determining hardware price.
Economics of a mobile radio network 225
Table 8.4
An Example of a Spreadsheet for Subscriber Unit Calculations
Basic assumptions (all prices in $)
Consumer mobiles 300
Business mobiles 500
Cost of sales 100
Annual price reduction 7%
Subsidy 50%
Year
1998 1999 2000 2001 2002 2003
Mobiles sold/year
(in thousands)
Consumer mobiles 50 150 300 500 500 300
Business mobiles 15 45 90 150 150 90
Consumer cost ($) 300 279 259 241 224 209
Business cost ($) 500 465 432 402 374 348
Annual cost ($million) 29.0 82.3 155.8 246.0 233.3 132.9
◗The base station and base station controller interconnection (i.e.,
connecting the base station to the switch) cost is dependent on the
interconnect method used (see Section 7.1.5). Leased lines result in
little capital charges but substantial operating expenditure. Micro-
wave links have the opposite effect on the business case.
◗The switching cost elements are typically comprised of the hard-
ware cost of the switch, the accommodation costs, and the costs of
providing back-up power supplies and security. Typically, the fail-
ure of a switch impacts heavily on the revenue since a large part of
the network will be out of operation and a range of measures are
taken to provide redundancy and ensure a very low level of failure.
The O&M systems will typically be costed with the switch.
Table 8.5 shows an example of a spreadsheet for a simple system
where base station interconnection is not required.
226 The Complete Wireless Communications Professional
Table 8.5
Example of a Spreadsheet for Network Cost
Basic assumptions (prices in $’000)
Base station cost 1, 50
Installation 1, 20
Planning 1, 5
Base station interconnect via microwave links
Cost 1, 70
Installation 1, 10
Switch costs 1,000
Switch installation 1,000
Year
1998 1999 2000 2001 2002
BSs installed 59 177 354 591 591
Switches installed 1 1233
BS total cost ($m) 9 27 54 91 91
Switch total cost ($m) 2 2466
Total cost ($m) 11 29 58 97 97
8.2.3 The operating expenses
As well as capital expenditure, there will be ongoing operational expendi-
ture in the form of:
◗Rental for the base station and base station controller sites;
◗Leased-line costs where used;
◗Maintenance on all the network equipment;
◗Costs of radio spectrum;
◗Subscriber management costs;
◗General management costs including buildings and facilities;
◗Marketing, sales, and subscriber retention costs.
Most of these are either self-explanatory or have been covered else-
where. Worth noting is the cost of maintenance, which is typically
around 1% of the cumulative capital expenditure; the cost of radio spec-
trum (see Section 12.3), which in some cases can exceed all other expen-
diture; the subscriber management costs, which include call centers and
sending bills to the subscriber; and the subscriber retention costs, which
may include discounts for long-term users or periodic free replacement
phones.
An example of a spreadsheet showing how some of these costs might
be modeled is provided in Table 8.6.
In this highly approximate example, where the base stations have
been interconnected by leased lines, the key costs are maintenance and
leased lines.
8.2.4 Revenue
This is where any attempt at science disappears and art takes over! In
principle, the calculation of revenue is methodological and is shown in
overview in Figure 8.1.
The various parts of this figure are described throughout this section.
In essence, the predicted number of subscribers is multiplied by the call
minutes per subscriber to derive the total call minutes. These need to be
segregated according to whether they were made in peak or off-peak peri-
ods. They need to be divided into incoming and outgoing calls. Finally,
Economics of a mobile radio network 227
they need to be divided according to their destination, with possible desti-
nations to:
◗The national PSTN;
◗An international PSTN;
◗Another mobile on the same network;
◗Another mobile on a different network.
Each of these different classes of call will attract a different tariff and a
different interconnect charge. Hence, for each of the different classes of
228 The Complete Wireless Communications Professional
Table 8.6
Example of a Spreadsheet Showing Ongoing Expenses
Basic assumptions
Average site rental ($’000/year) 1, 5
Cost per leased lines ($’000/year) 1, 15
Maintenance (%) 1, 2.5
Radio spectrum ($’000/year) 1,000
General costs $/sub/year 1, 10
Marketing costs $/sub/year 1, 10
Year
1998 1999 2000 2001 2002
Background information
Total subs (‘000) 65 260 650 1,300 1,950
Total sites 59 236 590 1,181 1,772
Ttl network cost ($m) 11 40 99 1,197 1,294
Ttl sub unit cost ($m) 29 111 267 1,513 1,746
Ongoing costs ($m)
Rental 0.2 1 2 1, 51, 8
Leased lines 0.8 3 8 1, 17 1, 26
Maintenance 1 3 9 1, 17 1, 26
Spectrum 1 1 1 1, 11, 1
General costs 0.6 2 6 1, 13 1, 19
Marketing costs 0.6 2 6 1, 13 1, 19
Total ($m) 4 14 35 1, 68 1,101
calls the total call minutes is multiplied by the tariff and the interconnect
costs as shown in Figure 8.1. The total revenue is equal to the total call
fees charged to the subscriber less the interconnect costs for those outgo-
ing calls terminating on a different network but plus the interconnect
costs for those calls originating outside the mobile network and terminat-
ing within.
This much seems reasonably scientific and can readily be encoded
into a spreadsheet. A simplified example of the revenue side (ignoring
interconnect) for a single type of call (say calls made during the peak
period to the national PSTN) is shown in Table 8.7. However, the diffi-
culty is in obtaining the estimates of the total subscriber numbers, min-
utes of usage, and call destinations. For a network already in existence,
these can be extrapolated from existing records. For a new network,
knowledge of other networks in the same or similar countries can provide
valuable input. Nevertheless, this is essentially a forecasting role, with the
skill set that such a role entails. Typically, the complete wireless profes-
sional would rely on the marketing department to derive such informa-
tion based on:
Economics of a mobile radio network 229
Predictions as to
subscriber numbers
Predictions as to call
patterns and volumes
per subscriber
Predictions as
to tariffs
Outgoing call
revenue
Calculation of total
volumes of each call
type and hence total
revenue
Predictions as to
interconnect fees
Incoming call
revenue
Calculation of total
volumes of each call
type and hence total
interconnect
fees receivable
Outgoing call
costs
Calculation of total
interconnect fees
payable
Sum of costs and
revenues to arrive
at overall revenue
Figure 8.1 Overview of the calculation of revenue.
◗Data from existing networks;
◗Demographic information;
◗Information about the wealth of the populace;
◗Information about existing use of telephony;
◗Predictions for GDP trends and population trends;
◗Awareness of relevant changes such as an increase in home
working;
◗Guess work!
Predicting interconnect fees can be relatively simple since these are
often published by the PTO, but the prediction of tariffs can be difficult.
Few would doubt that tariffs would fall in the future, but estimating by
how much is nearly impossible. An interesting exercise is to understand
the minimum tariffs at which it is still profitable to operate the network
230 The Complete Wireless Communications Professional
Table 8.7
Example of a Spreadsheet for Predicted Revenue
Annual subscription/customer ($) 100
Fall in subscription/year 10%
Call minutes/subscriber/year 1,600
Cost/minute ($) 0.4
Rise in usage/year 10%
Fall in cost/minute each year 15%
Bad debts 5%
Year
1998 1999 2000 2001 2002
Ttl subscribers (‘000) 50 200 500 1,000 1,500
Ttl subscriptions ($m) 5 18 40 70 90
Call minutes (millions) 80 352 960 2,080 3,360
Cost/minute 0.40 0.34 0.29 0.25 0.21
Less bad debts 5% 5% 5% 5% 5%
Ttl call revenue ($m) 30.4 113.7 263.6 485.4 666.5
Ttl revenue ($m) 35.4 131.7 303.6 555.4 756.5
and to assume that, at the worst case and in a price war, tariffs might at
some point fall to this level.
In reality, considerably more complex spreadsheets than that shown
in Table 8.7 would be required.
It is worth considering the interconnect arrangements in more detail
since this is a subject of some complexity. Interconnect is payable when-
ever the call originates on a different network than that on which it termi-
nates. The user in the originating network is charged for the call and then
the originating network pays a fee to the terminating network for carry-
ing the call. Different interconnect fees will be payable depending on the
destination of the call. Interconnect revenue results from calls that are
made to mobiles. Table 8.8 shows a simplified interconnect calculation for
a single subscriber over the period of a year where the tariff is the amount
charged to the mobile user for making the call, while the cost is the inter-
connect fee paid to, or received from, other operators.
In this example, the difference between peak and off-peak rates has
not been shown nor has the interconnect arrangements relating to roam-
ing mobiles (i.e., mobiles registered on a different network). The PSTN is
the fixed network, while the public land mobile networks (PLMNs) are the
mobile networks. The figure shows that considerably more fees are
received for terminating incoming calls than are paid to other operators
for terminating outgoing calls, and as a result the net interconnect reve-
nue is significant. Note also the assumption that the mobile originates
slightly more calls than it receives, which is typical for mobile subscribers.
Recently, interconnect fees for calls made from the PSTN to the
mobile network have been a subject of much scrutiny in the EC. These
fees are typically very high, leading to the cost of calling to a mobile being
high. This results in a higher revenue for the mobile operator. Many sus-
pect that the mobile operator will attempt to reduce the tariffs they charge
their users since the users are well aware of these but increase the inter-
connect costs since few callers from the fixed network are aware of the
cost of calling a mobile. In this manner, they can appear to be relatively
inexpensive to their users. Mobile operators typically deny that this is the
case and claim that the cost of terminating these calls is high; but since
they charge more for terminating a call arriving from the PSTN than they
do for a mobile-to-mobile call on the same network, which uses twice the
resources, there is clearly some need for further investigation in this area.
It seems likely that in the future, balanced and fair interconnect rates
Economics of a mobile radio network 231
232 The Complete Wireless Communications Professional
Table 8.8
A Simplified Interconnect Calculation
Call minutes per subscriber/year 1,600
Increase in call minutes 10%
Percent Tariff $/min Cost $/min
Incoming calls
From PSTN 24 — 0.42
From other PLMN 9 — 0.19
From own PLMN 7 — —
International 7 — 0.08
Outgoing calls
To PSTN 25 0.47 0.06
To other PLMN 11 0.28 0.22
To own PLMN 8 0.22 —
International 9 0.75 0.06
Interconnect revenue in
$/subscriber/year Year
1998 1999 2000 2001 2002
Incoming calls
From PSTN 160 176 194 213 234
From other PLMN 28 31 34 37 41
From own PLMN 00000
International 9 10 11 12 14
TOTAL 197 217 239 263 289
Outgoing calls
To PSTN 22 24 27 30 33
To other PLMN 39 43 47 52 57
To own PLMN 00000
International 8 9 10 11 12
TOTAL 69 76 84 92 102
Outgoing less incoming 128 141 155 170 187
will become increasingly prevalent as regulatory pressure forces mobile
operators to move in this direction.
8.2.5 Financing
Financing is the process of deferring payment in the early years of the net-
work. It is effectively the borrowing of money. This is often required by
mobile radio operators since they must make an investment in the net-
work before they recoup that investment through call charges. Although
at the highest level this would seem to be simply a case of borrowing
money, there can be considerable complexity in the manner in which
financing is achieved.
The mobile radio operator is looking for a source of borrowing at the
lowest possible rates of interest. The lenders are looking for a way of mak-
ing a return on their money at the lowest possible risk. The complexity
arises in meeting the objectives of both parties. Often, investment in a
mobile radio operator will be looked upon as relatively high risk since the
timescales before repayment can be long and, particularly for the third
and fourth mobile radio operators in a country, there is little evidence
that they will be successful. Banks may not be willing to lend money
against such a high perceived risk.
In outline, the options available for borrowing are:
◗Self-funded from reserves within the group;
◗Direct funding from banks or other financial institutions;
◗Vendor financing from the equipment manufacturer;
◗Shareholder funding.
The first option is only open to large companies who have substantial
cash reserves and is becoming increasingly rare. It has the advantage of
the operator not having to take any action to secure the funding.
The second option of borrowing from financial institutions is also
relatively straightforward. There is typically no loss of control of the com-
pany and repayment schedules can be set to meet the requirements of
both parties. Most banks will see a mobile telecommunications project as
a high-risk investment and will only want to take a limited stake in order
Economics of a mobile radio network 233
to reduce their exposure; as a result, it is typically not possible to generate
all the funding required from bank lending.
There have been many vendor-financed sales in recent years where
the manufacturer essentially provides their equipment for free and then
is paid back as the network becomes profitable. In principle, there should
be little need for vendor financing since there exist many other sources of
financing. Vendor financing is normally used where the risk is considered
so high that no other party is prepared to make the investment at a rea-
sonable rate of interest. It is worth asking why, if the loan is so risky, the
vendor might be prepared to take it on. There are a number of reasons for
this.
◗The vendor sees this as the only way to sell equipment on which
they will make a profit—however, if the company collapses they
will not realize their profit.
◗The vendor is in a better position to judge the risk than the bank
because they typically have a better understanding of the industry.
◗To some extent, if the operator fails the vendor can remove their
equipment and sell it to a different operator, effectively reclaiming
part of their loan; whereas banks will typically not be able to sell any
equipment that they reclaim.
Basically, the manufacturer is expected to provide funding by defer-
ring the payments on the equipment or alternatively the equipment can
be used as a means to purchase equity (shares) in the company and the
manufacturer then becomes a shareholder in the operator. Manufactur-
ers reluctantly agree to such projects if it is the only way in which they will
sell equipment. However, vendors themselves can only borrow certain
amounts of capital and cannot finance all the projects for which they are
asked. Many vendors will have problems with high levels of financing
because this will result in poor sales figures for the year because the
financed sales cannot be realized on the books until a cash payment is
received. Hence, an operator may have to select a vendor other than that
selling the most appropriate technology if vendor financing is required.
For this reason, a number of institutions such as the European Bank for
Reconstruction and Development (EBRD) are rather wary of vendor-financed
projects, preferring to select the technically most appropriate equipment
rather than the operator who can provide the most funding.
234 The Complete Wireless Communications Professional
Shareholder funding generates revenue through the use of an initial
public offering (IPO) that places the company on the stock market. Typi-
cally, it is not possible to perform an IPO until the network has already
started to be rolled out and there is some revenue from subscribers to
allow investors to better understand the viability of the company. As a
result, shareholder finance can only be used during the later stages of a
network (typically not until at least one year from license award and
often two). Shareholder funding has the advantage that there is little
need for repayment schedules to be met but the disadvantage that some
of the control of the company passes to the shareholders.
For a more detailed introduction to financing methods, readers are
referred to [4].
8.2.6 Summary
Having calculated the total expected capital, ongoing costs, and the
incoming revenue, the next step is to compare the two in order to deter-
mine whether the selected balance of coverage, service, and tariffs meets
the business requirements. There are many ways of examining the infor-
mation (again, readers who desire a full introduction to project financial
analysis should consult [4]). The first step is to compare the total expendi-
ture with the total income. This is shown for the simple example in
Table 8.9.
The spreadsheet shows an unusually profitable network (deliberately
made so to keep the example simple); in practice, much longer break-
even times are likely. Nevertheless, it adequately and simply demon-
strates some of the key financial analysis that is required.
One key statistic immediately visible is the total funding requirement.
The network will need to borrow over $45M during 2000 before starting
to repay the loans in following years. This is a key input into the funding
analysis.
Another key figure is the time to break even. This is shown in
Figure 8.2. This shows that the break-even point was achieved approxi-
mately four years after the network was constructed.
The financial measures quoted most often are the net present value
(NPV) and the internal rate of return (IRR). These are derived from the cash
flow for each year, which is in turn derived as the revenue less the expen-
diture for that year.
Economics of a mobile radio network 235
One of the most appropriate ways to evaluate a project is to consider
the NPV, which looks at the total outgoings and incomings over the
length of the project, weighting money spent or received during future
years by a factor accounting for the cost of capital over this period.
Management texts agree that this is the most appropriate way to evalu-
ate a project. In principle, any project with a positive NPV should be
undertaken.
Another investment measure that is widely used is the IRR, which
effectively provides a measure of the interest that is gained on the money
236 The Complete Wireless Communications Professional
Table 8.9
Example of a Spreadsheet Showing Summary Financial Statistics
Basic assumptions
Interest payable on loans 10%
Year
1998 1999 2000 2001 2002
Handset subsidy ($m) −29 −82 155 246 233
Capital spend ($m) −11 −29 58 97 97
Ongoing spend ($m) −4−14 35 68 101
Revenue ($m) −29 −107 248 453 616
Profit ($m) −15 −18 −141 183
Borrowing ($m) −15 −35 −41 −3179
Interest payable ($m) −1−3−4−0.3 0
Bank balance ($m) −17 −39 −45 −4179
−100.0
−50.0
0.0
Bank balance ($m)
50.0
100.0
150.0
200.0
12345
Years of operation
Figure 8.2 Cumulative profit by year.
invested in the project. If the IRR is higher than the cost of borrowing the
money, or the return that can be achieved from investing it elsewhere,
then the project should go ahead. IRR is widely disliked in management
texts because, were there two mutually exclusive projects, one with an
IRR of 20% and an investment of $100M and the second with an IRR of
30% and an investment of $20M, there is clearly a much larger absolute
amount of profit to be made on the first project simply because of the
larger sums involved. Because IRR does not consider the total sum
invested, only the equivalent interest gained, a company would, incor-
rectly, select the second investment. Hence, NPV is considered a more
appropriate investment mechanism. IRR is, in fact, closely related to NPV
analysis—the IRR is nothing other than the discount rate, which, if
applied to an NPV analysis, would yield an NPV of exactly zero.
In order to calculate the NPV, the preceding table needs to be rear-
ranged slightly to look at inflows and outflows and cost of capital.
Table 8.10 shows that when considered as a 5-year project (in prac-
tice, most mobile networks will be considered over 7 to 10 years but 5 was
selected here for simplicity) the project has a NPV of $117M. In principle,
any project with a positive NPV should be undertaken.
In practice, NPV can be calculated most simply using the “NPV” func-
tion in most spreadsheets.
Economics of a mobile radio network 237
Table 8.10
Example of a Spreadsheet Showing NPV Calculations
Assumption Discount factor 10%
Year
1998 1999 2000 2001 2002
Discount −1−0.9 −0.8 −0.7 −0.6
Total outgoings ($m) −44 126 249 411 432
Discounted ($m) −44 113 202 300 283
Total revenue ($m) −29 107 248 453 616
Discounted ($m) −29 −96 200 330 404
Total ($m) −15 −16 −1−30 120
Cumulative ($m) −15 −32 −33 −3117
References
[1] Allen, M., and D. Myddelton, Essential Management Accounting, New York:
Prentice-Hall, 1992.
[2] Dyson, J., Accounting for Non-Accounting Students, London: Pitman, 1991.
[3] Emmanuel, C., D. Otley, and K. Merchant, Accounting for Management Control,
London: Chapman and Hall, 1990.
[4] McLaney, E., Business Finance for Decision Makers, London: Pitman, 1991.
238 The Complete Wireless Communications Professional
Operating a mobile
radio network
Business has only two basic functions—
marketing and innovation.
Peter Drucker
9.1 Introduction
Operating a cellular network consists of both
keeping the network working and monitor-
ing usage so that areas where congestion
might occur can be predicted. Where conges-
tion is expected, network capacity enhance-
ment will be required. It is also important
to understand marketing policies since
changes in areas such as tariffs can lead
to a sudden dramatic increase in usage.
The complete wireless professional should
understand:
◗How statistics are generated and proc-
essed regarding the daily operation of the
network;
239
Contents
9.1 Introduction
9.2 Monitoring the
network
9.3 Tariff policies and
their implications
9.4 Capacity
enhancement
9
CHAPTER
◗The implication of changes in marketing on the network design;
◗Ways to enhance the capacity of a radio-based network once con-
gestion is predicted.
9.2 Monitoring the network
It is important to continually monitor the operation of the network in
order to enable:
◗Delivering statistics about the network so that the need for addi-
tional resources can be monitored;
◗Changing network configuration;
◗Monitoring the correct working of the network and raising alarms
when failures occur;
◗Allowing new subscribers to be entered onto the network database
and old ones deleted;
◗Monitoring the network for fraudulent use;
◗Generating bills for users;
◗Providing customer care by monitoring usage, providing new fea-
tures, and managing supplementary services.
Delivering network statistics Network statistics are vital to ensure
that the quality of service parameters for the network are being met. The
key statistics include:
◗The percentage of time for which all the channels in a cell are in use
(note that the network cannot directly return a blocking statistic
because, by definition, it does not know about blocked calls; how-
ever, if all the channels in a cell are in use, it is a good indication that
blocking might exist);
◗The percentage of calls that have been dropped, which provides
information on quality of signal strength, quality of handover, and
possible interference problems;
240 The Complete Wireless Communications Professional
◗The voice quality as measured in GSM by a function termed
RX-QUAL (received quality), which estimates the voice quality
based on the number of received blocks in error;
◗Network downtime resulting from a failure of a part of the network.
With these statistics, the operator is able to determine the changes
that are required to the network in order to reach targets. For example,
where cell sites are congested, more channels can be added or microcells
installed in order to increase the capacity. Where dropping is problematic,
a team can be sent to investigate whether the problem is related to inter-
ference or coverage.
The biggest problem with network statistics is making sense of the
vast amount of data that the network can provide, running to gigabytes of
information per day. Sophisticated software packages are now available
running on a central data collection unit that sifts through the data look-
ing for patterns and evidence of specific problems.
In the future, manufacturers are predicting that, using statistical
information, networks will be able to self-optimize, deciding on the fre-
quency assignment and the cell neighbors for the purpose of handover.
To do this, the measurements made by the mobiles on the signal strength
in the surrounding cells will be passed back to a central database, as well
as used to make a handover decision. By analyzing the signal strength
from surrounding cells as perceived by hundreds of mobiles in a given
cell, an accurate picture of interference and neighbor cells can be built up.
It is thought that this sort of application will be deployed from 1999
onward.
Changing network configuration When it is determined that a net-
work needs to be modified in order to improve the quality of service for
the subscribers, it is typically necessary to change the network configura-
tion. For example, if microcells are to be added in an area, it may be neces-
sary to remove some frequencies from the macrocells and to replan the
macrocell frequency assignment. In a typical network, large-scale con-
figuration changes are made three to four times a year. All the base sta-
tions must be changed within a few minutes of each other since during
the change process there is likely to be poor network quality because
some base stations are using the old parameters and some the new. The
only way to achieve this coordinated change is via the use of a central
device able to run a batch file with all the change instructions in place and
Operating a mobile radio network 241
send all the appropriate commands to the different base stations. This
function is performed by the operations and maintenance center (OMC).
Monitoring the correct working of the network Subscribers will
judge a mobile radio network based on the quality of service that they
receive. This is composed of a combination of blocking, lack of coverage,
and network failure time. Any network that has long periods of down-
time will lose revenue both directly through the calls that cannot be car-
ried while the network is down and indirectly through the loss of
subscribers who find the quality of service too low. To help overcome long
periods of down time it is essential that the functions of the network are
continuously monitored. This is achieved through the function of the
OMC, which provides a centralized terminal on which all the functions of
the network can be monitored. In a system such as GSM, the interface to
the OMC has been standardized so that components from different
manufacturers, such as BTSs, can all interwork with the same OMC. In
GSM, each of the base stations reports back on its correct operation to the
BSC that controls it. The BSC is then responsible for reporting back
to the network management system both about its own functionality and
the functionality of all the BTSs under its control. This reporting takes
place along the A-interface link from BSC to MSC and then along the
E-interface link from MSC to MSC before finally arriving at the OMC.
Adding and deleting subscribers When a potential new subscriber
enters a shop and buys a phone, he or she now expects that phone to be
working by the time he or she returns home. In order to activate the
phone it is necessary to register it onto the HLR and provide it with an
appropriate service record. Billing records also need to be generated,
although they do not need to be in place quite as quickly as the HLR regis-
tration. In order to achieve this, shops will often be connected to a distrib-
uted computing system (e.g., an Intranet) that allows them to send
electronic registration messages into the network that can be forwarded
to the HLR. Obviously, a similar process is required to delete subscribers.
Monitoring fraud Fraud has been an increasing problem for network
operators for some time. Although the process of cloning analog phones is
reducing as more subscribers use digital phones, there are still problems
with theft of phones and with complex call-forwarding call schemes.
Generally, once a phone is stolen or forwarded the fraudsters know that
they have very little time to make the most of the phone before the
network operator catches up with them. As a result, they tend to use
242 The Complete Wireless Communications Professional
the phone almost continuously and for international calls. Network
operators try to catch such behavior by monitoring the usage of each
phone. If it suddenly increases substantially, particularly with interna-
tional calls, the fraud-monitoring system running on the billing platform
may shut the phone down. Clearly, there will be difficulties in finding a
balance between rapidly stopping fraudulent use and allowing users to
change their calling habits, for example, as the result of a new job.
Generating bills Within GSM, each call generates an electronic billing
record. This is forwarded to the billing system in the home network where
it is held against the subscriber generating the call. At the end of the
accounting period (typically a month), the billing system automatically
produces a printed bill detailing all the calls made and the charges pay-
able. Advanced billing systems even automatically insert the bill into an
envelope.
Operators are demanding increasing flexibility from the billing sys-
tem to deal with a wide range of tariffs and special offers, for example.
Consider that one operator has a range of different tariffs and promises
that each month the billing system will select the tariff most suited to that
user and bill them accordingly. As packet data systems arrive, billing will
become even more complex. As a result, it will not be unusual for expen-
ditures on billing systems to reach many tens of millions of dollars and for
lead times on developments of the platform to be the key constraint in
launching a new service.
Providing customer care Customer care systems might provide the
customer with the help and information that they require to make better
use of the mobile phone. Examples include the provision of football
results, share prices, and similar data. To provide this service, a bridge
between the information providers and the mobile network is required.
When trying to add additional customer care features, the value of
having a system conforming to an open standard rather than being pro-
prietary can be very high. For proprietary systems, the operator is reliant
on the supplier to add any required features to the equipment and the
supplier may not be prepared to place the development of this feature
high on their priority list since they are now in a monopoly supply posi-
tion to this user. When an open standard has been procured, it is often
possible for third parties to provide software or hardware providing the
required functionality. A good example of this is within GSM where an
IN peripheral to the MSC has been defined, known as CAMEL (see
Operating a mobile radio network 243
Section 11.3). This allows third parties to provide software that can alter
the manner in which the switch from a different vendor operates.
Because the third party is under competitive pressure from other compa-
nies, the new features are typically provided more quickly, at less cost,
and often requiring less effort from the operator.
9.3 Tariff policies and their
implications
Tariff policies and network capacity are linked in a complex manner. It
might be imagined that if the tariff is reduced, then users will make more
calls with their mobiles. As a result, the capacity required from the net-
work will be increased. However, predicting the manner in which usage
will vary with traffic does not appear to be possible in any accurate fash-
ion at the moment. With this relationship in mind, a mobile radio opera-
tor might consider the required capacity for their network in a number of
different ways.
1. Capacity could only be provided as required by actual traffic
growth.
2. Capacity could be provided in advance of predicted growth to
provide a constant buffer against unexpected growth surges.
3. Capacity could be dramatically increased in order to be able to
reduce tariffs and attempt to gain significant fixed/mobile substi-
tution traffic and market share.
Fixed/mobile substitution is a key issue in the future progress for cel-
lular. In developed countries, most of the telephony traffic (around 98%
by volume) is still carried over fixed networks. However, some cellular
subscribers are now starting to see their mobile phone as their primary
means of communications and are making calls on the mobile phone that
would previously have been made on the fixed line. At present, the key
barriers to this continuing are the higher cost of mobile calls, the lower
voice quality, and the lack of reliability in terms of high blocking and
dropping rates. However, there have been many attempts to overcome
244 The Complete Wireless Communications Professional
these problems using reduced tariffs for calls made in home cells and simi-
lar. A network strategy that dramatically increases capacity and reduces
prices could result in a massive increase in cellular traffic.1
The strategy selected has a number of key impacts on the capacity
enhancement technique that should be adopted (and hence on the net-
work plan developed by the engineer). For example, in case (1) it is only
necessary to determine the least expensive means to provide the addi-
tional capacity. With cases (2) and (3) it is necessary to consider a number
of interrelated factors such as:
◗How the number of subscribers will grow in the coming years given
the tariffing policy;
◗How the traffic per subscriber will change given the tariffing policy,
subscriber mix, and extent of fixed/mobile substitution, which itself
will be influenced by coverage and blocking;
◗How the action of competitors will impact on the tariffing policy
and the total subscriber numbers, including areas such as fixed/
mobile integration and mobile computing;
◗Leading from these, how the revenue per subscriber will change as
a result of all these interrelated policies.
An intelligent operator might attempt to determine the tariff level at
which their revenue would be maximized, taking into account the total
revenue at any point and the cost of providing the necessary network
capacity. This calculation can be performed using a spreadsheet model if
some assumptions about the manner in which the usage would vary with
the traffic could be made. The complete wireless professional should be
able to work with the marketing and financial staff to determine where
the optimum point of network operation might lie.
Operating a mobile radio network 245
1. A strategy along these lines was adopted by One-2-One in the United Kingdom, who
offered free calls after 7 P.M. The result was a massive increase in traffic, with One-2-One
users generating over three times the average traffic on the other cellular networks.
Unfortunately, One-2-One was unable to economically expand their network to handle
this traffic and decided to discontinue the tariff. However, this clearly shows that with a
reduced tariff, dramatic increases in traffic volumes are possible.
9.4 Capacity enhancement
9.4.1 Introduction
In the case that demand for service exceeds supply and the blocking
increases it is necessary to enhance the capacity. This section looks
at means whereby the capacity can be enhanced. It considers only
GSM—typically other cellular networks are not yet in a position where
they need capacity enhancement, and hence the options for capacity
enhancement are much more limited. The logical approach to under-
standing capacity enhancement described here, however, should be
equally useful when considering other technologies.
9.4.2 The available capacity
enhancement techniques
We first seek to understand the underlying theory. The capacity of a cell in
terms of number of radio channels is given by
mB
BK
=t
c
(9.1)
where Btis the total bandwidth (spectrum) assigned to the operator, Bcis
the bandwidth required per call, and Kis the cluster size or reuse factor.
To enhance the capacity it is necessary to change one of the terms in this
equation. Each of the possible means is now considered.
Increase the total bandwidth Many operators are not able to gain
additional spectrum. However, recently there has been a trend toward
awarding dual-band spectrum. Dual-band operation is seen by many as a
means to increase their network capacity.
Reduce the bandwidth per call There is only one way to achieve
this, which is through the use of the half-rate coder. However, operators
have generally dismissed this coder as having inadequate voice quality
and it will not be considered here.2
246 The Complete Wireless Communications Professional
2. Actually, the picture here is still quite unclear. In 1997, all operators were saying that
half-rate would not be used because of poor quality. By 1998, some of these operators
were looking at half-rate deployments. Many operators are not publicly announcing their
intentions because of the politics of requesting further dual-band or UMTS spectrum.
However, as mentioned in Section 2.4.2, the most likely scenario appears to be operators
waiting for the advanced multirate coder before moving to lower speech coding rates.
Decrease the cluster size To decrease the cluster size it is necessary
either to decrease the interference transmitted into cochannel cells using
transmit power control,discontinuous transmission, multiple reuse patterns, or
concentric cells or to increase the tolerance to interference using techniques
such as frequency hopping and the enhanced full-rate coder.
Use more cells Since the equation describes the number of channels
per cell, simply increasing the number of cells will increase the capacity.
This could be through cell splitting,sectorization,microcells or picocells, and
underlay/overlay cells.
Changing one of the terms in this equation is the only means whereby
it is possible to increase the capacity of a cellular system. Measures from
all families could be used at the same time if required. The capacity gain
from each technique is now considered in a little more detail.
9.4.3 Dual-band operation
The maximum gain in the number of radio channels is simply given by
the percentage increase in spectrum (e.g., if the 1,800-MHz assignment is
the same size as the 900-MHz assignment, then the number of radio
channels is increased by 100%). This leads to even greater gains in traffic
capacity due to the trunking efficiency achieved, but here, for simplicity,
gains will only be discussed in terms of the increase in the number of
radio channels.3The maximum capacity gains can only be achieved if
there is at least as high a percentage of dual-band mobiles in use as the
percentage of the total assignment that the 1,800-MHz spectrum forms
(50% in this example). These gains also require algorithms to ensure that
mobiles are reasonably evenly distributed across the two bands, but in
principle this is not too difficult.
9.4.4 Techniques affecting the
cluster size
In a cellular system, the maximum capacity is achieved when the interfer-
ence is distributed evenly across all mobiles. This is a fundamental design
Operating a mobile radio network 247
3. To illustrate the trunking gains, assume that the operator had 2 ×12MHz at both 900 and
1,800-MHz frequency bands. Assuming an average cluster size of 15, this results in 4
carriers, or around 30 voice channels in each band. At a 2% probability of blocking, 30
channels provides 21.5E whereas 60 voice channels provides 49E; hence, a doubling in
spectrum provides a capacity gain of 2.27 as a result of the trunking gain.
concept in mobile radio systems. Imagine cell A using 10 frequencies and
cell B, some distance away, also using the same 10 frequencies. A system
designer wants to be sure that the interference on each of the frequen-
cies is sufficiently low that reliable communications can be made. Put
together, the mobiles in cell A are going to generate a certain amount of
radio signal. If this is not evenly divided across all frequencies, then one
mobile in cell B will receive more interference than the others. To make
sure that this mobile can communicate correctly, the cell needs to be far
enough away so that this interference level is acceptable. However, this
implies that on the other nine frequencies, the interference level is even
lower. This is great for those mobiles who get a better quality, but it means
that on those nine frequencies, the frequencies could have been reused
closer to cell A, resulting in a lower cluster size and greater spectrum effi-
ciency. Only if the interference is evenly distributed across all the mobiles
can the minimum cluster size be adopted and the maximum capacity
achieved. Choices made by operators about cell size and handover strat-
egy can also have a significant effect on interference.
An operator can do two things. One is to adopt one of two ways to dis-
tribute interference more evenly—either frequency hopping or a form of
dynamic channel allocation. The second is to reduce the interference gen-
erated using discontinuous transmission and power control. These are
now considered in more detail.
9.4.4.1 Distributing interference evenly
Frequency hopping To frequency hop, a mobile moves from fre-
quency to frequency while it is transmitting. Other mobiles in the cell are
also hopping from frequency to frequency and the sequence that each
uses is designed so that no two mobiles in the same cell ever use the same
frequency at the same time.
For any two mobiles using the same frequencies in cells that are some
distance apart, in some cases the mobiles will be as close to each other as
possible on the near edge of their cells, whereas in other cases the mobiles
are much further apart than in the worst case and hence will suffer less
interference. When designing a system without frequency hopping, the
designer must assume that the worst case will occur. Hence, the designer
must space cells using the same frequencies further apart than if the aver-
age case was assumed. This results in an increased cluster size and hence a
reduction in the overall system capacity. This is inefficient because in
248 The Complete Wireless Communications Professional
most cases, the worst case will not happen. When using frequency hop-
ping, the designer can assume that the average interference will be expe-
rienced by all mobiles and hence bring cochannel cells closer together.
There are two types of frequency hopping: synthesizer and baseband
frequency hopping. Synthesizer hopping is a technique where mobiles
hop over many frequencies (up to 64). In baseband hopping, the carrier
frequencies transmitted by the base station do not change and the mobile
just moves from carrier to carrier. Because there may only be two or three
carriers per base station, baseband hopping results in a much lower
number of frequencies to hop over and hence less randomization of inter-
ference. Synthesizer hopping should be used wherever possible.
Theory suggests that, depending on the design of the underlying net-
work and the existing cluster size, gains of around 50 to 60% in the
number of radio channels (and hence greater gains in the traffic carried
due to trunking efficiencies) can be achieved using frequency hopping.
Some operators have experienced larger gains than this, but these are
probably due to a network that was somewhat inefficient before the
capacity enhancement work started.
Dynamic channel allocation The other way to evenly distribute the
interference is to use DCA, where a cell does not have any frequencies
permanently assigned to it, but when a user requires a channel, the base
station selects that with the lowest interference. This removes the need
for frequency hopping since all channels can now be selected with con-
trolled levels of interference. DCA is not available within GSM, but a
simpler approach, known as concentric cells (also known as intelligent
underlay/overlay (IUO)) can be used that provides some of the gains of
DCA. Here the mobiles near the center of the cell use one transceiver
(TRX) while those on the edge use another. Those near the center are
transmitting with lower power and the “edge of the cell” generated by this
TRX is well within the edge of the cell generated by the other TRX. Hence,
it will be possible to reuse the frequencies in the inner cell much closer to
the first base station than those used in the outer cell. The inner cell will
have a smaller cluster size and hence more capacity is gained. This tech-
nique reduces the need to randomize interference because the interferers
in any particular cell are now more alike in their position in the cell
and transmitter power. Its key advantage is in reducing the cases where
spectrum is wasted because two cochannel mobiles are close to their
respective base stations and hence generating little interference.
Operating a mobile radio network 249
The maximum theoretical gain from DCA also depends on the cluster
size in the network before enhancement, but is typically around 50%. For
the concentric cell approach to achieve this, an infinite number of layers
of concentric cells would be required, so clearly the gains from concentric
cells must be below 50%.
Both frequency hopping and DCA achieve an even distribution of
interference, and both can provide similar gains of the order of 50%.
Since both achieve the same thing, there is little merit in using both
together. The only advantage would be to allow some frequencies to be
used that had too high an interference to offer acceptable voice quality. As
long as these are only hopped onto irregularly the reduction in quality
may be acceptable. However, this is a dangerous arrangement since a
reduction in signal strength could drop the call and this tactic should
probably be avoided. Hence, the maximum gains that could be achieved
with this set of techniques are probably around a 50% increase in traffic
channels. Because concentric cells are not a perfect form of DCA, using
frequency hopping as well does bring some gains over concentric cells
alone, but these gains are typically not significantly greater than what
could have been achieved with frequency hopping alone.
Multiple reuse patterns are very similar to concentric cells. The con-
cept is that the first TRX in the cell operates on a cluster size of, say 15; the
second on a 12 cell cluster; and the third on a 9 cell cluster. Quality is then
higher on the first and second TRX than the third, but because of the
reduced cluster size, the frequencies are reused more in the network.
Users can hop across all the carriers, resulting in an average quality level,
or can be directed away from the low-quality carriers by intracell hando-
ver in the case that their call quality is suffering unduly. The result may be
something like a concentric cell—only those mobiles near the cell center
will be left on the low-quality carriers because they will have a better sig-
nal strength being closer to the transmitter.
In principle, multiple reuse patterns are not necessary—a reduction
in the cluster size on all TRXs coupled with frequency hopping will pro-
vide the best results. However, the TRX on which the system information
is provided—the so-called BCCH carrier—cannot hop for design reasons,
so it is necessary to use a larger cluster size for this carrier. Hence, the opti-
mal design is typically a two-tier reuse pattern with a reuse of say 15 for
the BCCH carrier and perhaps 9 for all the other carriers, all of which are
using frequency hopping.
250 The Complete Wireless Communications Professional
9.4.4.2 Interference reduction
Discontinuous transmission and transmit power control reduce the inter-
ference levels since the mobile and base stations now transmit for less
time and with less power. Typically, these techniques only bring benefits
when coupled with frequency hopping that will spread the reduction in
interference around all the mobiles, helping to reduce the cluster size. The
gains here are difficult to predict and depend on the existing cell planning,
handover strategy, and other capacity enhancement techniques in use.
In summary, the capacity enhancements that can be achieved using
cluster size reduction techniques will depend on the underlying network,
but up to 50% can be achieved by evenly distributing the interference,
and perhaps a further 50% by reducing the interference.
9.4.5 Using more cells
Most operators have already embarked on the path of sectorization and
cell splitting. Actually, sectorization does not provide the capacity gains
that might be expected. Because the cell radius is unchanged, the effec-
tive transmitted power (the EIRP) remains unchanged and hence the
reuse distance remains unchanged. However, each sector needs a differ-
ent frequency, so the result is that the cluster size after sectorization is
greater than the cluster size before. Worse, the lower number of channels
in each sector compared with those in the cell reduces trunking effi-
ciency. In practice, careful use of antenna directionality can provide some
gains, perhaps up to a 100% increase, but sectorization does not multiply
the capacity by the number of sectors introduced as might initially be
thought. Its widespread use is due to its cost-effectiveness since additional
cell sites are not required.
Microcells, as the name suggests, are cells that are significantly
smaller than the current cells used within a network. For the network
operator, the key issue is how many and where microcells are to be
deployed. There are two main strategies:
1. Hot spot coverage, where isolated microcells are placed in areas
where there is a lot of radio traffic (e.g., train stations);
2. Contiguous coverage of a region where microcells are used to
cover at least all the main streets within a given region.
Operating a mobile radio network 251
The problem with the former is that it is often difficult to locate traffic
hot spots; they may only be temporary and may expand or move so
that the original microcell placement becomes inappropriate. However,
because only a small number of microcells are deployed, the costs are
relatively low. Contiguous coverage overcomes the problems of locating
hot spots by providing coverage throughout the area. However, some
microcells may be minimally used, resulting in a more expensive deploy-
ment than need be the case.
In practice, an approach somewhere between the two is typically
adopted, where high-density regions are identified (typically cells where
high blocking takes place) and all the main streets within the coverage of
that cell are covered by microcells. This removes the need to locate the hot
spots to the accuracy of a microcell but ensures only those parts of the city
with relatively high traffic levels are covered.
The capacity provided by microcells is simple to calculate—typically
they have two carriers and, hence, provide around 15 voice channels.
Frequencies in a microcell cluster can be reused with a cluster size as low
as 4 due to the blocking effect of the buildings on the interfering signal.
Underlay/overlay systems are basically cellular networks where the
macrocells have been left in place while the microcells were deployed.
The aim of the operator is to carry most of the traffic on the microcells, but
if there is insufficient coverage, or if the mobile is moving rapidly and
would require numerous handovers in a microcellular network, then
they are placed on the macrocellular network. They do not increase
capacity significantly but make microcells more workable.
9.4.6 Which capacity enhancement
techniques should be used when?
Of course, the most appropriate capacity techniques to use depends on
the capacity enhancement required and on the state of the underlying
network. In this analysis it has been assumed that urban cells are already
sectored and are approaching the minimum radius (around 400m) practi-
cally possible for macrocells. Certainly, if there is dual-band spectrum
available, then it should be used (operators will typically never refuse
more spectrum). The costs of using this spectrum are mostly involved in
getting dual-band mobiles into the subscriber base, but as these mobiles
become more widespread, this will tend to happen in any case over time.
252 The Complete Wireless Communications Professional
However, for most operators this will only be a 50 to 100% capacity
enhancement—worth having but not sufficient to solve the capacity
requirements for all time.
The next obvious step is frequency hopping. This is within the GSM
standard and the mobiles are already capable of hopping. By hopping all
but the BCCH frequencies and reducing the cluster size on all the hopped
carriers, improvements in capacity of perhaps 50% can be achieved at
relatively little cost. Multiple reuse patterns or concentric cells could be
added in at this point, but after frequency hopping has been deployed the
gains from these other techniques are probably minimal and the effort
required to implement the techniques may be out of proportion to the
gains achieved. Only in the case of a badly designed original network
might they offer a way out of existing interference problems.
After this, the only option is the addition of more cells. Only cell split-
ting and microcells will provide significant capacity gains and in a well-
developed network, cell splitting is typically no longer possible. Microcells
can provide huge capacity gains—easily 500% or more in city centers, but
compared to the other techniques discussed earlier are relatively expen-
sive, requiring new cell sites and infrastructure—hence, the reason to use
them as the last capacity enhancement technique.
So the approach to adopt for capacity enhancement is relatively
straightforward:
◗Deploy dual-band spectrum if available.
◗Implement frequency hopping along with discontinuous transmis-
sion and power control.
◗Deploy sufficient microcells to provide the remainder of the capac-
ity required.
Operating a mobile radio network 253
Large users of
mobile radio
networks
That which seems the height of absurdity in
one generation often becomes the height of
wisdom in another.
Adlai Stevenson
10.1 Introduction
Most of the users of mobile radios are the gen-
eral public. These are individuals who have
varying needs from their mobile phones, but
for the majority the key needs are the ability
to make a voice call wherever they are for a
reasonable price and at a reasonable quality.
Today’s mobile phone systems coupled with a
well-designed network are able to provide
this requirement. It has often been predicted
that in the future the public will require more
data capabilities, perhaps the need for video-
phones, and other advanced capabilities. The
255
Contents
10.1 Introduction
10.2 Railways
10.3 Police
10.4 Other
emergency services
10.5 Other users
10
CHAPTER
ability for future mobile phone systems to provide these facilities is dis-
cussed in Chapter 11.
At the moment, the most pressing additional requirements come
from the existing large users of mobile telephony such as police and rail-
ways. These bodies use mobile communications as an integral part of con-
ducting their safety-critical roles. As a result, they tend to put a much
greater requirement on their mobile communications. Understanding
the needs of these users is important for a number of reasons.
◗The wireless professional may be working directly for these users
and so will need to understand their requirements.
◗Wireless professionals working for manufacturers will need to
understand the requirements of all the potential user groups in
order to correctly design their systems.
◗Wireless professionals working for PAMR and cellular operators are
likely to be involved in discussions with these bodies about the pos-
sibility of them moving away from self-provision and onto a shared
network.
◗The requirements of these large bodies may well become the
requirements of small companies in the future.
In this section, two key sets of users are examined in detail, the police
and the European railways. The police are representative of all the emer-
gency services and perhaps have the most difficult requirements of all to
meet. The European railways provide an interesting case because of their
recent decision to move from PMR technology to cellular technology. An
understanding of these two user groups will provide a good understand-
ing of most large PMR users.
Some important points to remember when reading both of these
descriptions.
◗The perceived requirements are often heavily conditioned by the
capabilities provided by the existing radio system; for example,
most existing systems can only provide group calls (and not point-
to-point calls), but this has become part of the way of working and
now many users cannot perceive operation without these features.
Some would argue that these features would not be required if the
way of working was modified. However, although the engineer
256 The Complete Wireless Communications Professional
can question a user’s requirements, if the user insists on these
requirements, the engineer has to accept them even if they do not
appear to be logical.
◗Both these organizations have existing departments responsible for
the provision of mobile communications. It is in the interest of the
people in these departments to make the requirements as complex
as possible to justify their existence. Outsourcing their communica-
tions requirements will seem to them a little like voting themselves
out of a job because if communications are outsourced, their role
will be much diminished.
◗There are differences between different countries. In Europe, PMR
users have the alternative of a robust and ubiquitous GSM system.
In the United States there is limited national roaming and only ana-
log AMPS networks that provide widespread coverage. Hence, in
the United States there is a greater need to implement a self-owned
system.
10.2 Railways
10.2.1 Introduction
Like almost all forms of transportation services, railways have been quick
to embrace mobile communications as a means to provide greater effi-
ciency and improved safety. It is difficult now to conceive of a complex
railway system being able to operate satisfactorily without mobile radio
communications. The current mobile systems, and the uses to which they
are put, are discussed in more detail below. With the EC directive on the
harmonization of the European High-Speed Network technology now in
place, coupled with the rapid development and introduction of relatively
advanced digital mobile radio systems, by the early 1990s the European
railways were looking for a new digital radio standard.
The railways noted the benefits of digital communications over the
current analog systems, including improved voice quality, greater secu-
rity, more flexibility, and better spectrum efficiency, and their view was
that railways could gain benefits through implementation of a digital
radio system. There was also a growing realization that the use of
Large users of mobile radio networks 257
proprietary systems was becoming increasingly expensive, both in the
specification and the procurement phases, and that standardized solu-
tions would be likely to be more cost effective.
In the early 1990s, the European railway body, the Union Internation-
ale des Chemins de Fer (UIC) decided to specify a digital radio system to be
implemented from 1998 onward to provide both pan-European opera-
tion and an advanced range of features currently not available in many
national radio systems. It is instructive to examine this project, named
EIRENE (European Integrated Radio Enhanced Network), and the man-
ner in which the new system is to be implemented.
The overall scope of project EIRENE was to provide a specification for
a radio system that could meet most requirements of the UIC European
member organizations. The initial study involved determining what the
needs were through examining the requirements documents compiled
by the railways and by conducting a series of interviews with different
railway authorities. These needs were then classified into sets of logical
requirements and compared with the features offered by current and
emerging communications systems, including those undergoing stan-
dardization. A detailed study was made of the most appropriate candidate
systems leading to a recommendation to use GSM. Shortcomings were
identified in the GSM capabilities, and modifications suggested to over-
come these. The final part of the feasibility study involved producing a
generic procurement specification for the proposed system.
10.2.2 Current railway
communications within Europe
European railway authorities operate a variety of mobile radio systems.
Indeed some countries have more than one system; British Rail, for
example, introduced three different systems between 1984 and 1986, all
of which were still in operation in 1998. Part of the reason for the number
of systems is the wide range of applications. Communications to drivers in
trains, between shunting teams or trackside workers, and among station
staff are all necessary. Currently, different systems are being used to fulfill
different roles.
Nevertheless, there is a fair degree of commonality among European
track-to-train mobile radio communications systems, with many being
based on a UIC standard known as 751-3, originally issued in the early
258 The Complete Wireless Communications Professional
1970s. This document, or fiche as it is more commonly known, allows for
simplex and duplex conversations to drivers, including the capability to
make group calls and emergency calls. The system is based upon an
analog FM standard with 25-kHz channel spacing operating around
460 MHz. Provision is made for tone signaling, including a number of
single frequency tones to indicate channel-free, listening, warning, and
pilot tones, for example. In addition to the ubiquitous voice communica-
tions, short data messages can be sent using two-tone FSK.
In the 751-3 standard a particular frequency is assigned to each geo-
graphical area, and when entering that area the mobile should automati-
cally switch to the assigned frequency. The channel is essentially open in
that anyone can transmit on the channel and anyone in the vicinity can
listen, although in practice some form of privacy is made available
through selective calling and lockout procedures.
In essence, the current railway system described in fiche 751-3 is a
PMR-type system dedicated to a small range of applications. Unfortu-
nately, owing to implementation differences, the 751-3 systems in differ-
ent countries are often incompatible. Because of this, international trains,
such as those destined to run between Britain, Belgium, and France via
the Channel Tunnel, are being equipped with “chameleon” radios, capa-
ble of operating on each of the different radio systems. This chameleon
radio required a common specification for all three countries that has
proved to be a complex and time-consuming task. A new pan-European
radio standard would clearly ease this problem in the future.
Because 751-3 has only been designed for a limited range of railway
needs, it is difficult to provide the communications facilities for applica-
tions such as maintenance and on-train reservations without excessively
wasting radio spectrum.
10.2.3 Railway requirements
Before specifying an appropriate pan-European mobile radio system, it
was necessary for the railways to determine their requirements. Once
these were established, the tradeoff between cost and utility for each item
could be reviewed and the functionality needed from the radio system
established. A well-designed system should be capable of meeting all cur-
rent requirements and allowing some room for expansion, without being
overspecified.
Large users of mobile radio networks 259
There is a surprisingly wide range of railway requirements, partly due
to the fact that the railways both run trains and maintain infrastructure.
The most obvious requirements are for controller-to-driver communica-
tions. Controllers are members of staff responsible for a particular section
of track; they must perform signaling and communications functions to
provide a smooth and safe passage for trains, and they must act as an
emergency contact if problems develop. There may be a number of con-
trollers for a particular stretch of track, each associated with various
aspects of train control. Controllers need to be able to contact individual
drivers and groups of drivers within their area. Messages from drivers also
include emergency broadcasts that need to be rapidly relayed to all staff
within the area.
In addition to controllers, there are other individuals who may wish
to contact personnel on the train, the latter including drivers, guards, and
catering staff. The call originators might include other drivers, staff at sta-
tions, and staff supervisors, for example, and message types may include
voice, facsimile, data, text, and interactive computer messages. Such calls
may in the future be international.
With a view to improving the network capacity and efficiency,
remote control is envisaged by some railways. As well as the remote con-
trol of entire trains, this might include remote control by one driver of a
multi-locomotive train or remote control of items such as points and
level-crossing barriers. The radio system is a potential bearer for auto-
matic train control communications, gradually removing the need for
costly fixed signaling infrastructure.
A number of railway tasks are performed by teams that require local
communications. Such tasks include shunting, trackside maintenance,
and local communications at stations. Communications are typically over
a short range and involve groups whose membership might change on a
daily basis. In the case of trackside maintenance, the team may be work-
ing in a remote location where radio infrastructure has not been installed,
and so direct mode (or set-to-set) communications, where one handheld
radio communicates directly to another rather than via a base station,
may be required.
In addition to these operational requirements, a number of passenger
facilities can be envisaged, such as database access for timetable informa-
tion and advance booking, passenger information concerning delays, and
entertainment and news facilities. If trains are to compete successfully
260 The Complete Wireless Communications Professional
with aircraft on intra-European routes, such passenger facilities may be
needed.
Finally, some other constraints were imposed by railway operations.
These were:
◗Communication to and from high-speed trains are required, poten-
tially traveling at up to 500 km/h. Few radio systems are designed to
cope with the rapidly changing radio channels caused by the
Doppler shift associated with traveling at this speed.
◗Station staff will normally want to call a train by its running number
(a number corresponding to a particular timetable entry such as
“the 15H55 from London to Paris”) rather than by a telephone
number. This is because the 15H55 from London may be a different
physical locomotive each day and so possess a different telephone
number, whereas the running number is relatively static. If the
locomotive radio only had a fixed telephone number, then trying to
remember or to determine the appropriate numbers as they change
each day would be problematic. However, the maintenance depot
will only know a locomotive by its engine number and will want to
call it using this. Both means of addressing the locomotive must be
possible. These issues are considered later in this section.
◗Very rapid call setup is required, particularly in emergency
situations.
10.2.4 PMR versus cellular
Given the wide range of railway requirements, the design of a mobile
radio system that could meet them all was destined to be problematic. The
decision was made to employ an ETSI-specified European standard
mobile radio system in order to reduce the design cost and achieve econo-
mies of scale through markets outside the railway arena. Given the wish
to employ a digital system, and the timescales for implementation of
1999, this essentially led to a choice between GSM, TETRA, or DECT,
of which DECT was rapidly ruled out owing to its short transmission
range and limited facilities. A comparison made in 1993 at the time when
the railways were making their choice of GSM and TETRA with the cur-
rent railway system is presented in Table 10.1.
Large users of mobile radio networks 261
Table 10.1
Comparison of a Range of Radio Systems Made During 1993
751-3 GSM TETRA
Technology Analog FM Digital TDMA Digital TDMA
Frequency 460 MHz 900 MHz 400 MHz
Effective bandwidth
per voice channel
25 kHz 25 kHz, 12.5 kHz with
1/2 rate codec
6.25 kHz
Call setup times <1 sec <10 sec <1 sec
Data facilities Basic Yes Yes
Group calls Yes No (except via
conference call facility)
Yes
Direct mode N/A No Under development
Wide area
communications
No Yes Possible
Maximum speed Not specified 250 km/h 200 km/h
Handover Limited Yes Yes
Roaming No Yes Yes
Authentication and
encryption
No Yes Yes
Status Available Available Standardization
ongoing
The fundamental choice falls between a public subscriber cellular-
based system, such as GSM, or a PMR-type system such as TETRA. The
difference between the two system types is in the basic mode of commu-
nications offered. In cellular systems, one-to-one connectivity over a
wide area is required, whereas in PMR, group and dispatcher calls (proba-
bly over a smaller area) are necessary. Historically, this has tended to
mean that in a cellular system a pool of channels is available within each
cell and when communications are required one channel is allocated to
each user who wishes to pass a message to another user. In a PMR-type
system, a channel is assigned to a group of users for the duration of their
conversation upon which they can listen and transmit relatively freely.
This fundamental difference concerning channel assignment makes cel-
lular and PMR difficult to reconcile.
It became apparent that neither type of system was capable of
meeting all the railway radio requirements. PMR-type systems have
allowed driver-to-controller communications in the past, but the increas-
ing volume of traffic; the requirements for one-to-one communications
262 The Complete Wireless Communications Professional
between a number of possible users on the train and the ground, even
across international borders; and the desire for a fully integrated radio
system for all aspects of railway work are making them less suitable. None
of the systems available offered operation at train speeds of up to
500 km/h without modification, nor the indirect addressing required to
facilitate railway communications.
A strong case could be made for either TETRA or GSM; what was
required was a combination of both systems. TETRA offered a better fit to
the railway requirements than GSM but presented a higher risk because it
was not standardized (much less available) at the time. In contrast, GSM
was rapidly becoming a global success. It was therefore decided by the
railways that the risks involved in meeting the timescales were lower for a
GSM system with modifications than for TETRA.
With the selection of GSM, a range of modifications to the GSM stan-
dard to fill the shortcomings identified in Table 10.1 were put in place.
These form part of the GSM Phase 2+ features and are discussed in more
detail in Chapter 13.
10.3 Police
10.3.1 Introduction
The police forces make widespread use of mobile communications. Most
policemen on foot and police cars are equipped with mobile radio sys-
tems. Current systems, much like the railway systems, are typically
open-channel PMR systems. These offer a number of advantages to the
police in that with the open channel everyone in a particular area can
hear what is going on and take appropriate action. A policeman can talk
to the controller at the police station simply by pressing a button, and the
simplicity of open channel working ensures that the call setup is less than
a second, which may be important in some life-threatening situations.
However, these simple radios also have a number of problems. One of
the key problems is an increasing lack of radio spectrum. If all communi-
cations need to be heard by all users in an area, then they need to be on
the same frequency. One frequency can only accommodate a limited
number of users, and with the demands of modern policing this limit has
been met in many areas. Analog systems can be readily overheard by
criminals, which is a significant problem. The police are also increasingly
Large users of mobile radio networks 263
making use of mobile data for a wide range of tasks such as number plate
checking, mobile fingerprint analysis, and the use of video information
transmitted to officers. The police can envisage a dramatic increase in the
future of mobile data applications. Designs of the police helmet of the
future show a helmet with a built-in video camera and eyepiece, with
video being transmitted back to the control center and images transmitted
to the eyepiece of the helmet showing pictures of suspects and other rele-
vant details. It is quite clear that modern police communications will need
to be based around the most advanced digital communications systems
possible.
10.3.2 Description of requirements
The requirements of the police force are wide-ranging and include:
◗Point-to-point communications with encryption and a call setup
time of less than 1 sec;
◗Group and broadcast calls to a subset of users or to all users with a
1-sec setup time and the capability for acknowledgment of receipt;
◗Data communications at as high a rate as possible, with both
circuit-switched and packet data capabilities;
◗Direct-mode communications so that policemen out of radio cover-
age can communicate with each other;
◗Relay-mode communications where a mobile within the coverage
area can relay communications to a mobile outside of the coverage
area;
◗Rugged handsets that will withstand everyday use;
◗End-to-end encryption on all important calls;
◗International interoperability so that police forces from more than
one country can cooperate in cross-border operations;
◗The ability to communicate with ambulance and firemen during
emergencies;
◗High capacity in city areas but good coverage in rural areas;
◗A host of supplementary services, such as the capability for a
controller to turn on the mobile of any of their members of staff
264 The Complete Wireless Communications Professional
without the mobile making any noise, allowing the controller to
hear what is going on—this might be useful if a policeman is held
hostage.
Meeting all these requirements is clearly going to be difficult. The dif-
ficulty arises in matching the simplicity and speed of the wide area emer-
gency broadcast with the complexity of the point-to-point encrypted call.
10.3.3 Selection of radio system
The police forces throughout Europe, like the railways, performed a
detailed assessment of all the available mobile radio standards against
their exacting requirements. Unlike the railways, they concluded that
GSM would not be able to meet their needs. It may appear strange that
the police came to different conclusions from the railways because, in
general, as can be seen from the preceding descriptions, the requirements
of the police and the railways are actually quite similar. In the case of the
police, the need for encryption is higher and there is a perceived need for
a faster call setup (although many point out that since help will typically
take many minutes to arrive, the difference between a 1- and a 2-sec call
setup may not be one of life and death). Many are of the view that the
police requirements could have broadly been met by a modified version
of GSM in the same manner that the railway’s requirements were being
met. However, for a range of reasons, the police decided to adopt the
emerging TETRA standard for their own communications needs. Because
the standard was still in development at the time, the police were able to
add the additional features to the standard that they required and ensure
that the system was tailored to their needs.
As well as the selection of the radio standard, police forces in Europe
are often facing other changes in the manner in which their mobile com-
munications are provided. As can be envisaged from the list of require-
ments, the new radio system is likely to be substantially more expensive
than the existing radio system. Most police forces are under pressure to
reduce expenditure, and this pressure extends to the mobile radio system.
The basic way to reduce the cost of a system of this sort is to share the sys-
tem. Indeed, a moment’s analysis shows that if the system is not shared
among more users the cost will be very great.
In the United Kingdom there are around 95,000 policemen. A radio
network to cover most of the country would require around 1,000 base
Large users of mobile radio networks 265
stations. Hence, there will be on average 95 policemen per base station
(many more in cities, many fewer in rural areas).
With a cellular network, there are around 3 million subscribers on the
two main networks in the United Kingdom. The cellular operators have
deployed around 2,000 base stations to provide coverage and capacity.
Hence, there will be on average 1,500 subscribers per base station.
Clearly the cost of a shared public system will be dramatically lower
than the cost of a dedicated police system. In order to reduce this cost bur-
den, police forces have been looking at sharing their network with ambu-
lances and fire crews. However, this will less than double the user base. In
the United Kingdom, the attempt at sharing has been taken a step further
with the instructions to the police that they must seek a private company
to build their network, with the police paying an annual fee for the use of
the network. The intention is that the winning company will be able to
use shared resources such as the backbone network and many of the mast
sites in order to reduce the cost of the system to the police. Further sharing
could take place with TETRA users on PAMR networks, although the
police are keen to retain their own radio spectrum so that they do not suf-
fer from their network being blocked by other users during an emer-
gency. Whether these approaches will be successful remains to be seen.1
10.4 Other emergency services
In this category fall the ambulance and fire services and some smaller
organizations such as the coast guard and similar groups. Mostly the
requirements of this group are a subset of those of the police. Because the
groups are generally smaller, their requirements often get subsumed into
police systems and they may end up sharing technology. For an ambu-
lance service, the key requirements are:
◗Dispatching (the sending of an ambulance to an incident);
◗Status reporting (an ambulance telling the controller what it has
found and what it is doing about it);
◗Two-way text messaging (information and instructions);
266 The Complete Wireless Communications Professional
1. At the time of writing only one consortia was interested in providing this service, with
other competing consortia having withdrawn. This was raising concern that the
remaining consortia was effectively in a monopoly supply position.
◗Automatic vehicle location (AVL) in order to allow the controller to
establish the location of all his or her resources.
Of these requirements, often the most difficult to meet on a standard
radio system is AVL as this may require short data bursts every, say,
10 sec. Where the radio system only supports circuit-switched communi-
cations, then this can tend to be highly inefficient of resources. Support-
ing AVL efficiently requires a packet-based data communications system.
A fire brigade has similar requirements but may also need:
◗The ability to send building plans over the radio system, requiring
high-speed data capabilities;
◗The ability for the radio in a fire vehicle to act as a repeater to fire-
fighters inside the building who may be out of coverage from the
base station.
Most ambulance and fire services employ the same type of radio sys-
tem as the police, and in Europe it is currently envisaged that all the emer-
gency services will share a TETRA system.
10.5 Other users
There are many other users, as shown by Table 4.2, and covering them all
would take some time. All have simpler needs than the railways and the
emergency services discussed here.
Utilities such as gas, electricity, and water typically require good voice
communications; the ability to send data; possibly the capability to
remotely read meters, or to remotely interrogate customer databases; and
good coverage along the pipelines and electricity pylons, for example. The
latter is problematic as these often tend to be in rural areas where there is
generally little coverage. Utilities require the capability to preempt calls in
the case of an emergency, such as a gas explosion. It is typically the cover-
age and the preemption requirements that tend to result in the utilities
deploying their own systems rather than sharing PAMR or cellular sys-
tems, but the increasing cost of self-deployment and the improvements in
shared systems have meant that the utilities are slowly moving away from
Large users of mobile radio networks 267
self-provision, though again they are reluctant to give up their own fre-
quencies and systems.
The requirements for organizations such as delivery companies are
relatively simple. They wish to send itineraries to vehicles at the start of
the day and for the vehicles to be able to send proof of delivery notifica-
tions as they deliver their cargo. They would also like AVL. These require-
ments can all be met by a data-only system such as some of the public
packet data networks in operation. However, the companies typically also
like voice backup so that they can speak to the driver in the case that
something unexpected happens. Such organizations now rarely have
their own systems, typically using either PAMR or public data systems.
268 The Complete Wireless Communications Professional
Future mobile radio
systems
Everything has been thought of before, but
the problem is to think of it again.
J. W. von Goethe
11.1 Progress in radio
systems
As discussed in Chapter 1, the first true
cellular systems were the analog networks
introduced in the mid-1980s. These are only
now being phased out as the second genera-
tion of radio systems, the digital cellular tech-
nologies, are coming to the fore, some 12 to
15 years after the analog systems. The digital
systems are better, with better voice quality,
better security, more services and data capa-
bilities, and an increase in capacity. However,
the increase is relatively small. Some opera-
tors have even claimed that they got more
capacity from their analog systems than their
digital systems, although this generally seems
to be a result of using the same base station
269
Contents
11.1 Progress in radio
systems
11.2 The third
generation vision
11.3 Designing the
third generation system
11
CHAPTER
sites, which may not be ideally positioned for digital. A quick calculation
shows that TACS-type systems have voice bandwidths of 25 kHz and clus-
ter sizes of 21. GSM has the same voice bandwidth but an average cluster
size of around 12 in most deployments. The capacity gain is therefore
around 75% over 15 years. Given the rapid increase in the size of com-
puter files that users might wish to send, it can be seen that mobile radio
systems will have problems keeping up with the demands that users
might place upon them.
As discussed in this chapter, the next generation of products will
probably be well established to the extent that they rival second genera-
tion systems by around 2010, another 12 or so years away. It is too early
to understand the capacity that will be offered, but an estimate of a fur-
ther 75% increase is unlikely to be highly inaccurate. Services will be
improved, but the average user may not notice a large difference. This
chapter looks at the developments of third generation systems. Since the
situation is currently changing rapidly, the interested reader will need to
seek additional sources of information such as the ETSI web site [1].1
11.2 The third generation
vision
Although, to some extent, the next generation of radio systems is simply
an opportunity to update existing mobile radio systems as advances in
technology and manufacturing have occurred, many of the standards
bodies have attempted to set out their vision of what the standard should
provide. There are four main parties involved: the ITU at an international
level, the national regulators in Japan and Europe, and the CDMA devel-
opment group, mostly based in the United States. Most parties agree that
the goals of the next generation system should be “communication to
everyone, everywhere.” Communication in this instance might also
include the provision of information. To achieve this goal it must provide
all the facilities required for a wide range of disparate users including:
◗Cellular users who require high voice quality and good coverage;
270 The Complete Wireless Communications Professional
1. As an aside, learned journals cannot be recommended as an up-to-date source of
information. It now takes longer to publish a paper in most learned journals than it does
to publish a book!
◗Users who currently deploy their own private systems (see
Chapter 4) who require group and broadcast calls where all users
can hear what one person is saying;
◗Paging users who require a small terminal and good coverage;
◗Cordless users who require excellent communications with high
data rates when in the office or home;
◗Satellite users who require truly worldwide coverage;
◗Users in airplanes who currently have limited telephone availability
(especially to receive calls);
◗Data users ranging from telemetry to remote computer network
access.
The system must also provide fixed mobile convergence such that
users can get a similar service from a fixed or mobile connection, ideally
using the same phone number. Current predictions as to the timescales of
third generation systems vary slightly but typically the following is
assumed:2
Standardization completed 1999
First product available 2002
Product widely available 2005
The current view is that GSM will evolve to provide third generation
features, and hence it is necessary to obtain an understanding of GSM
evolution in order to understand how the third generation will develop.
GSM evolution GSM is currently evolving to provide many but not all
of the features of third generation systems [2]. Some of the key features
being added to GSM as part of the Phase 2+feature set include:
◗The advanced speech call items: The advanced speech call items (ASCI) are
defined as group and broadcast calls, and priority and preemption.
Broadcast calls allow many users to listen to a single radio channel
in a cell and for the call to be available in many cells. Group calls
Future mobile radio systems 271
2. These appear optimistic, and as discussed in Section 13.3, it would be no surprise to find
the timescales slip by as much as 3 years.
allow users to respond after the call originator has finished speak-
ing. Preemption allows a priority to be attached to the call and for
other calls to be curtailed if there are no other resources available
for a high-priority call.
◗A packet data service known as general packet radio service: General packet
radio service (GPRS) allows packet-switched communications. As
can be seen from the discussion in previous chapters, this will pro-
vide increased efficiency in a range of applications, including Inter-
net access. However, it requires a significant change to the GSM
system. Alongside each MSC is a GPRS support node (GSN),which is
basically a packet switch. There is then a separate packet network to
support the GSNs and interconnect them. By sending packets on
more than one time slot to the same user, data rates of up to
150 kbps can be achieved. There are many difficulties such as how a
mobile listening on the GPRS channels for packets is able to receive
paging messages—in this case, paging messages are also relayed on
the GPRS channels, requiring careful integration between the GSN
and MSC. It will be interesting to monitor the evolution of GPRS; as
increasing volumes of data are transmitted over mobile phone net-
works it could be that GPRS becomes the dominant bearer in the
GSM network. GPRS is seen by many operators as a stepping stone
toward a UMTS system that will be predominantly packet based.
Use of UMTS will help them understand the requirements, tariffs,
and uses of packet data.
◗A higher data rate service known as high-speed circuit switched data:
High-speed circuit-switched data (HSCSD) provides a higher data rate
than can be achieved at present by concatenating timeslots
together. If 6 timeslots are used, then data rates of 64 kbps can be
achieved. The only problems are the loss of capacity from giving one
mobile a number of timeslots and the difficulty for the mobile in
making measurements of surrounding cells when it has to listen to
more downlink frames than normal.
◗Intelligent network capabilities, known under the misleading title of cus-
tomized applications for mobile network enhanced logic: Customized appli-
cations for mobile network enhanced logic (CAMEL) allows subscribers
to make use of operator-specific services even when they have
roamed to a different network. For example, an operator might
272 The Complete Wireless Communications Professional
offer its subscribers call forwarding depending on the time of day so
that during the day calls are routed to the office and in the evening
to the home. This is not part of the GSM standard but could be
implemented with custom software in an MSC. However, when
roaming, the subscriber would not be able to access such a service.
CAMEL requires visited networks to send back event notes to the
home network and then await further instructions. This leads to an
architecture very similar to the IN in fixed networks, as described in
Chapter 6.
◗The SIM toolkit: The SIM toolkit is a package of measures that
revolves around giving the SIM card some processing power and
allowing it to interact with the mobile. By downloading applica-
tions onto the SIM card, new services can be provided to the user.
For example, the operator may wish to offer a service whereby the
user can book theater tickets using the mobile phone. The network
would send a list of shows to the SIM that would then instruct the
phone to display these to the user and return the answer to the SIM.
The SIM would then instruct the phone to send a coded message
back to the network so that the tickets can be ordered. The SIM
toolkit coupled with CAMEL will go a long way toward allowing
operators to provide personalized services to users wherever they
are and whatever phone they are using.
◗The enhanced full-rate codec: The enhanced full-rate codec (EFR) is a bet-
ter voice coder, providing a higher speech quality by taking advan-
tage of improvements in speech coder technology since GSM was
designed, not to reduce the coding rate but to enhance the voice
quality toward fixed-line quality. This coder has already been
widely deployed in the US GSM1900 networks and is expected to
become widespread in Europe by 1999.
◗Combined DECT/GSM handsets: These are handsets that can work on
both technologies, allowing use on DECT indoor systems as well as
GSM outdoor systems. At the time of writing, there seemed little
support for this feature.
There are other possible evolutionary paths to third generation.
The cdmaOne forum has proposed a wideband CDMA system called
cdma2000 that is similar to the UMTS proposals, although the
Future mobile radio systems 273
bandwidths for the two systems are slightly different because each has
been designed to allow easy interoperability with the existing uses of the
spectrum in Europe and the United States. The IS-136 system also has an
evolutionary path termed D-AMPS++, although this appears to be less
well supported than UMTS and cdma2000 and may not become a key
contender.
It seems likely that by the year 2005 there will be a new generation of
cellular systems capable of higher data rates than can currently be
achieved and using dual-mode capability to communicate with satellites
when out of the range of terrestrial phone systems.
11.3 Designing the third
generation system
One of the prerequisites of the third generation system was that it would
be accepted worldwide as a single global system, achieving the design aim
of international roaming. However, recently this has started to look like
an increasingly unlikely outcome. There are broadly three key players in
third generation work—Europe, the United States, and Japan.
Work on designing the third generation mobile radio systems has
been difficult. Each country wanted standardization decisions that pro-
vided benefits for its manufacturers. The Japanese were keen that the
third generation system not be based on GSM because they had not
achieved a high penetration of the GSM market. The Americans required
a system that aligned with the spectrum spacing they had already
assigned for second generation systems from the third generation band.
The Europeans wanted a system closely aligned to GSM so that they could
maintain their dominant position. The most visible sign of conflict was the
selection of the air interface.
Selecting the air interface is only one of a number of decisions. For
GSM it has been estimated that the air interface only contained 10% of
the specifications; the remaining 90% covered the manner in which the
core network (i.e., the switching system and BSCs) interworked. Hence,
it might have been thought that it would be the core network that
attracted most interest. However, the core network is based on numerous
existing standards, such as SS7, which there is little inclination to change;
274 The Complete Wireless Communications Professional
in any case, changes to the core network do not impact on the spectrum
efficiency. As a result, most bodies were prepared to accept that the core
network should be based on GSM with the required upgrades.
The air interface decision for UMTS was supposed to be reached in a
scientific manner. There were five key proposals for the air interface:
Alpha wideband CDMA (W-CDMA);
Beta orthogonal frequency division multiple access (OFDMA);
Gamma wideband TDMA;
Delta TDMA with spreading (WB TDMA/CDMA or TD/CDMA);
Epsilon opportunity driven multiple access (ODMA, a technique
whereby mobiles relayed messages to other mobiles).
Groups worked in parallel to evaluate each of the different techniques
over a period of approximately one year. Each group was given the same
scenarios, and the intention was that the results from each group would
be comparable, allowing an access technology to be selected according to
which best met the requirements. During this process, manufacturers
started to align themselves behind their preferred solution, typically that
in which they had the greatest intellectual property rights. The Alpha pro-
posal was based on Japanese suggestions concerning the third generation
access technology, which was also similar to proposals from cdmaOne
manufacturers for an evolution of their system. Hence, there was some
hope that if Europe could accept the Alpha proposal, a unified global stan-
dard might result.
At the meeting when a decision was scheduled to be reached about
the most appropriate access scheme, the following points were noted.
◗It was shown that ODMA could be an enhancement to any of the
other air interfaces and, hence, could be withdrawn from the
decision.
◗All of the remaining proposals had been shown to meet the UMTS
requirements.
◗All concept groups had performed extensive simulations, but each
had tailored the simulations to show their system in the best light,
with the result that each group could claim that its system was bet-
ter than the others!
Future mobile radio systems 275
◗There was strong support from the manufacturers for the Alpha and
Delta proposals that they justified in terms of their technical merits,
but was clearly based more on commercial considerations.
◗The Delta concept made enhancements to its proposal at a late
stage, but was not able to perform simulations, so it became even
more difficult to assess the relative merits.
◗There were numerous requirements for the air interface, and it was
not possible to reach agreement on which requirement was the
most important.
As a result it was not possible to select an air interface scheme on its
technical merits, despite the fact that the stated intention was to select the
scheme that was technically the most appropriate! This is not surprising
given the remarks in Chapter 13; engineers should realize that issues such
as the way the standard can be marketed, the management of risk,
and the network features provided can be as important as the techni-
cal capabilities of the standard. Perhaps it was unsurprising after the
TDMA/CDMA debate had characterized the second generation (see
Section 14.4) that a technical evaluation was not successful, but it should
be remembered that for future standardization any evaluation must look
more widely than technical merit.
Eventually, ETSI took a vote on whether the Alpha or Delta schemes
was most preferred, but the vote was inconclusive, not achieving the 71%
required by ETSI rules to make a decision. At that point the “politicians”
suggested that both the Alpha and Delta schemes could be adopted, the
Alpha scheme being used for paired spectrum bands and the Delta
scheme for the unpaired bands. The engineers were sent to find some jus-
tification as to why this would be an appropriate solution. The compro-
mise satisfied both parties who were able to agree on the selection of the
air interface. However, at the time of writing it is still unclear whether
this will result in a more complex and less efficient radio system than
would otherwise have been the case. An article in the Financial Times on
February 24, 1998, claimed that the reason that a compromise had been
reached was because the U.K. government unusually expressed its pref-
erence. It selected the Alpha scheme because it hoped it would result in a
single global standard. The issue of government intervention is discussed
in Appendix B.
276 The Complete Wireless Communications Professional
Design work on the third generation systems is scheduled to continue
until the end of 1999. There will be many more hard decisions en route
that will need to be solved in a similar manner to the air interface selec-
tion. The result may be a system that the big manufacturers are able to
control through their IPR and that is unlikely to upset the status quo in
the mobile radio world.
References
[1] http://www.etsi.fr.
[2] Zvonar, Z., and P. Jung, eds., GSM Communications Towards Third Generation
Systems, Berlin: Kluwer, 1998.
Future mobile radio systems 277
Regulators and
governments
Increasingly the world of mobile radio
communications is being dominated more
by the decisions of regulatory bodies than of
research laboratories and engineering depart-
ments. Radio spectrum, as mentioned earlier,
is essential for mobile radio communications;
hence, an understanding of the policies
adopted in the distribution of radio spectrum
is important for the complete wireless profes-
sional. Government regulations constrain
operators, preventing them from taking cer-
tain courses of action and artificially favoring
certain technologies by putting in place barri-
ers to others. The other side to regulation is
the use of standards, mandated by many
European regulators. This section also exam-
ines the standards-making process, looking at
the way in which the complete wireless pro-
fessional should partake in standards forums.
IV
PART
Radio spectrum
I would suggest the taxation of all property
equally, whether Church or corporation.
Ulysses S. Grant (1822–1885)
12.1 Introduction
Radio spectrum is the one critical resource for
all mobile radio communications. Without
access to radio spectrum, there can be no
mobile radio. As discussed in Chapter 2,
spectrum is a scarce entity and ways are
required to ensure that only the most appro-
priate users are given access to it. Under-
standing the way in which spectrum is
managed and controlled is essential for the
complete wireless professional. This chapter
looks at spectrum from the viewpoint of the
spectrum manager.
281
Contents
12.1 Introduction
12.2 The management
of radio spectrum
12.3 Modern
allocation and
assignment methods
12.4 Implications for
the mobile radio
operator
12.5 Government
policy
12
CHAPTER
12.2 The management of radio
spectrum
The world of radio spectrum management is composed of a number of
institutions. The most important of these is the ITU. (This was previously
known as the CCITT (Central Committee for Telephony and Telegraphy.)
The outline structure of the ITU is shown in Figure 12.1. Each sector also
has study groups that are not shown.
The International Telegraph Union was set up around 1865 after
20 European states decided to meet to work out a framework agreement
for international telegraphy. They also decided on common rules to
standardize equipment to facilitate interconnection, adopted uniform
operating instructions, and established common international tariff and
accounting rules.
Following the invention of the telephone in 1876 and the subsequent
expansion of telephony, the Telegraph Union began to draw up interna-
tional legislation governing telephony. With the invention in 1896 of
wireless telegraphy, it was decided to convene a preliminary radio confer-
ence in 1903 to study the question of international regulations for radio-
telegraph communications. A convention was signed in 1906, and the
Annex to this convention formed the first draft of the Radio Regulations.
In 1927, the Consultative Committee for International Radio (CCIR) and
the Consultative Committee for International Telegraphy (CCIT) were estab-
lished, with the CCIR made responsible for coordinating the technical
282 The Complete Wireless Communications Professional
Plenipotentiary
Conference
Council
Telecommunication
standardization sector
Telecommunication
development sector
World Radio
Conference
Radio
Regs
Board
Radio
Assembly
Radiocommunication
sector
Figure 12.1 The structure of the ITU.
studies, tests, and measurements being carried out in the various fields of
telecommunications and for drawing up international standards.
At the 1932 Madrid Conference, the Union decided to combine the
International Telegraph Convention of 1865 and the lnternational Radio-
telegraph Convention of 1906 to form the International Telecommunica-
tion Convention. It also decided to change its name and was known from
January 1, 1934, as the International Telecommunications Union. After
the first satellite was launched, the CCIR set up a Study Group responsible
for studying space radio communication in 1959, and an Extraordinary
Administrative Conference for space communications was held in 1963
to allocate frequencies to the various space services. In 1989, a Plenipo-
tentiary Conference decided to increase the importance of technical assis-
tance to the developing countries and set up a Bureau for the Development of
Telecommunications (BDT) to aid telecommunications development in the
Third World.
Each of the key parts of the ITU structure that affect radio communi-
cations policy are now considered.
Plenipotentiary Conferences determine key areas of policy and decide on
the organization and activities of the ITU. Their decisions are detailed in
the International Telecommunication Constitution and Convention. The
Plenipotentiary Conference is composed of delegations representing all
members and is convened every four years. The duration of Plenipotenti-
ary Conferences is normally limited to four weeks.
The ITU Council is composed of forty-six members of the Union elected
by the Plenipotentiary Conference. The role of the Council is to con-
sider broad telecommunication policy issues in order to ensure that the
Union’s policies and strategy are in accord with the changing telecommu-
nication environment.
Radio communication conferences are held every two years along with a
Radio Communications Assembly. The main function of radio communi-
cation conferences is to review and revise, as necessary, the Radio Regula-
tions on the basis of an agenda adopted by the ITU Council following
consultation of the membership. The general scope of the agenda is estab-
lished four years in advance and the final agenda is established by the ITU
Council two years before the conference. Radio communication confer-
ences may also recommend to the Council items for inclusion in the
agenda of a future conference and give its views on forthcoming agendas
for conferences.
Radio spectrum 283
These conferences are often fraught as each country tries to negotiate
a settlement that meets its own interests. Like standardization, discussed
in Chapter 13, there is little that is based on engineering judgment. Deci-
sions are made by regulators based on the difficulties they expect in clear-
ing the frequency bands and whether they expect the decision to aid their
local industry (e.g., because their industry has a lead in a particular prod-
uct at a particular frequency). Large organizations often resort to lobbying
tactics in order to press their case. Some allocations will be justified on
engineering grounds, but typically this justification supports rather than
drives the allocation process. At the end of the conference, the ITU recom-
mendations are updated.
Generally, the only engineers able to participate in these conferences
are those belonging to the national regulator. These will have studied the
problems for many months and understood the potential interference
resulting from particular decisions. Engineers from operators and manu-
facturers can only observe the proceedings.
Radio communications assemblies provide the technical basis for the
work of world radio communication conferences; approve the program of
work of radio communication study groups; and decide on the priority,
urgency, and timescale for the completion of their study. Radio commu-
nication study groups are groups of experts provided by administrations
and public/private sector bodies. They study technical questions relating
to radio communication issues and adopt recommendations. The focus of
study is on the use of the radio-frequency spectrum in terrestrial and
space radio communications (including the geostationary-satellite orbit),
the characteristics and performance of radio systems, the operation of
radio stations, and the radio communication aspects of distress and safety
matters.
The Radio Regulations Board approves the Rules of Procedure, considers
any matter that cannot be resolved through the application of the Rules of
Procedure, and performs any duties related to the assignment and utiliza-
tion of frequencies and to the equitable utilization of the geostationary-
satellite orbit. It also investigates cases of harmful interference and for-
mulates recommendations for their resolution.
An ITU recommendation looks something like the stylized version
shown in Table 12.1.
Recommendations cover the entire radio frequency band for three
different regions of the world, namely:
284 The Complete Wireless Communications Professional
1. Europe, Russia, and Africa;
2. North and South America;
3. The rest of the world (China, Australia, Asia-Pacific).
The text in capitals is known as the primary allocation. A user with
such an allocation is able to generate as much signal as they like within
their allocated band, with no concern over any interference this may
cause to other users. Any text in lower case is known as a secondary allo-
cation. A secondary user must not interfere with the primary user, nor
must they complain if they receive any interference from the primary
user. This only typically works where both users are stationary so that the
secondary user can plan their system based on a knowledge of the trans-
mission characteristics of the primary user.
Within Europe, there is a subsidiary spectrum management body
known as the CEPT. Members from spectrum administrations in Euro-
pean countries attend meetings in order to decide by consensus on pan-
European spectrum allocation issues. Usually, a member country or a
standardization body states an interest in a pan-European allocation for a
particular application. Study teams are then appointed to assess the spec-
trum requirements for the new service, the most appropriate frequency
bands to use, and whether members can make radio spectrum available
for this application. Finally, they recommend what spectrum should be
allocated and this recommendation is put to a vote by all the members. In
some cases, members may not accept the recommendation due to exist-
ing use of the spectrum. If the proposal is generally supported, then the
allocation becomes accepted by the CEPT, which may note that the allo-
cation will not become available in some countries in the near future.
Radio spectrum 285
Table 12.1
A Stylized Example of an ITU Recommendation
Frequency Band 1.455 to 1.460 GHz
Region 1 Region 2 Region 3
FIXED FIXED SATELLITE
aeronautic (note 234) MOBILE fixed
Studies into the particular uses of radio spectrum often have little to
do with engineering, despite their apparent engineering focus. Typically,
they will be staffed by engineers both from the company that wants the
assignment and the company that is currently using the spectrum.
Because of the difficulties in calculating modern radio spectrum issues,
agreement is difficult to reach. An interesting example was when consid-
ering the required guard band between TETRA and GSM systems at
900 MHz, apparently a simple engineering problem. The GSM users (who
already had a system in operation) wanted a worst case analysis, when a
TETRA mobile was only 1m away from a GSM mobile. The TETRA users
(who were hoping for the largest possible allocation) wanted an average
analysis where the distribution of the interference was determined and some
level, such as the 95% probability point, was used to determine the interfer-
ence. The difference between the two analyses was vast, and both parties
were determined that their approach was most appropriate. It is then for the
politicians to determine a compromise solution acceptable to both parties.
Most spectrum management work is performed at a national level by
a government, or a government-appointed body such as the FCC in the
United States. These bodies have control over which particular users are
allowed to use the band and police the use of the radio spectrum. They are
also responsible for determining the most appropriate manner to distrib-
ute the radio spectrum.
The world of spectrum management is becoming increasingly diffi-
cult. Pressure on the radio spectrum is growing rapidly from a wide range
of sources. There are many new applications that are seeking radio spec-
trum such as WLL and satellite systems. Existing applications such as cel-
lular radio systems are continually seeking additional spectrum such as
the UMTS allocation. Because such users realize the potential profit from
the use of radio spectrum, they can often be vociferous in their claims for
spectrum, taking recourse to legal action if they are not satisfied. This
places pressure on the spectrum manager to be able to clearly justify any
allocation and assignment decisions that they might make.
Spectrum managers are also often under pressure from their own
governments to show that they are maximizing the value that the coun-
try receives from the radio spectrum and to demonstrate that they are act-
ing in a transparent and open fashion. As lead by the United States,
governments are also increasingly expecting spectrum managers to sell or
lease the spectrum and realize capital gains for the government.
286 The Complete Wireless Communications Professional
The next section discusses the tools that spectrum managers have
available in order to help them overcome these new challenges.
12.3 Modern allocation and
assignment methods
In the past, most spectrum management decisions were taken on a judg-
mental basis. A company would apply for some spectrum and the spec-
trum manager would assess who was currently using the band and
whether the existing user should be displaced to make way for the new
user, or encouraged to share with them. Such an approach was successful
when the number of applicants was relatively small and the spectrum
manager sufficiently skilled, but judgmental approaches are generally not
transparent and can be difficult to prove conclusively in a court of law.
Increasingly spectrum managers have turned to economic tools to help
them with their task of allocating spectrum.
The most obvious approach, and one that gained much publicity in
1997 in the United States, is the use of auctions to distribute radio spec-
trum. This is intuitively simple—the spectrum that is available is given to
the highest bidder. Auctions have much to recommend them, they are
relatively simple, they can distribute spectrum rapidly, and they have the
happy side effect of raising revenue for the government. They are easily
defended in law and can be seen to be transparent and open.
However, there are a few problems with auctions. The first is that
radio spectrum must first be cleared of existing uses before it can be auc-
tioned,1so the spectrum manager still has to make a decision about which
bands to clear for which applications. To some extent, the spectrum man-
ager is helped in this task by international regulations, but these can only
provide guidance. The next is that the design of the auction is critically
important. Auction theory is a complex area and is explored in more
detail in Section 12.4. There have been some auctions of radio spectrum
Radio spectrum 287
1. Actually, there is a variant of the auction where the spectrum is offered with the existing
user (the “incumbent”) still in place. The winner must then decide whether to work
around the existing user or to compensate them sufficiently that they move to a different
frequency band. There are many problems with this approach with the incumbent often
holding the new operator to ransom for use of the radio spectrum, and the spectrum
manager often ends up intervening to solve the problem.
in the past where, due to poor auction design, the results have been so
embarrassing to the government that ministers have resigned. The U.S.
auctions have also highlighted another problem known as “winner’s
curse” where many of the winners have subsequently gone bankrupt.
This issue is also looked at in more detail in Section 12.4.
As mentioned previously, auctions can only be used once a decision
has been made to clear a band. There are a number of techniques that can
be used to help clear a band and to show which users value the band most
highly. The most straightforward of these is the use of economic pricing.
In this technique, existing users are charged a substantial fee each year for
use of the spectrum, equivalent to a rent. This fee encourages them to
return any unused spectrum, to make the most efficient use of the spec-
trum that they already have, and to consider whether moving to a differ-
ent frequency band might be more economic. To work, the prices need to
reflect the demand for the band, such that the most congested bands have
the highest prices per megahertz. In principle, the price should be set at
the “market rate” for the frequency band, which is the rate that would be
paid were the spectrum traded on the open market. The market would
push up the price for the spectrum until supply and demand were equal.
Herein lies the problem with economic pricing. Determining the market
price, without making use of market forces, is very difficult [1, 2] and can
only be estimated by looking at the alternatives available to existing users
of radio spectrum and the costs that they will incur in taking up these
alternatives. The price of the spectrum is then set at a level where it is
worthwhile for enough users to move out of the band that there will no
longer be congestion.
Spectrum pricing is due to be deployed in the United Kingdom in
1998 after much study, consultation, and legislation; it will be interesting
to see how well it works in encouraging more efficient use of the radio
spectrum. Like auctions, it also has the happy side effect of raising reve-
nue for the government.
Of course, it is possible to establish a market for radio spectrum and
allow real market forces to set prices, overcoming one of the key problems
with spectrum pricing. The simplest way to achieve this is to allow users of
radio spectrum to buy and sell their spectrum with other users. By this
means, a market in spectrum is developed and the prices set by the market
can be used to determine the most appropriate use for the spectrum. At
present, few spectrum managers are prepared to go as far as trading. They
288 The Complete Wireless Communications Professional
are concerned about the loss of control of the radio spectrum that this
would entail because this might result in it being difficult to meet interna-
tional obligations for the use of the spectrum bands. There may also be
difficulties should the spectrum manager wish to reclaim spectrum for
any reason—in this case, they would probably need to buy it on the spec-
trum market. Finally, the revenue from the spectrum will not pass to the
government but to the existing users of the spectrum in the form of
a windfall gain. To overcome this problem, trading is only normally
allowed in spectrum that has first been auctioned so that the value of the
spectrum is received by the government in the first instance, although
users may then make gains themselves if the value of their spectrum
appreciates. Trading has been used in Australia and New Zealand where it
appears to be successful. However, both of these countries have the
advantage of geographical isolation that allows them to change the use of
their radio spectrum with little concern for the interference it might cause
to their neighbors.
In order to enable trading, the spectrum manager needs to allow a
market to develop. To do so, they need to publish a register of who holds
what spectrum and to provide an agency that can put people who want to
sell their spectrum in contact with people who want to buy. The agency
should also keep track of the sale price of each piece of spectrum as this sends
important signal as to the value of the spectrum and the possible need to auc-
tion more spectrum in particular areas where there is a high demand.
Finally, the spectrum manager can attempt to assess the value of the
spectrum to the country directly. In principle, if the value that the country
derives from each of the different uses of the radio spectrum can be esti-
mated, then the spectrum manager can take spectrum from one use that
is deriving little value and give it to another use that is deriving a greater
value. This approach is known as economic value analysis. To do this,
each part of the radio spectrum band is studied to determine what value
the country derives from the use. The value is composed of the operators
profits and expenditure on the local economy plus the value that the
users derive, over and above the fees they pay for using the system. Like
spectrum pricing, deriving these values is difficult and experience in
the United Kingdom has shown that substantial effort is required to
even approximate the value. Nevertheless, the process of attempting
the estimation is a valuable one in providing important information to the
spectrum manager.
Radio spectrum 289
12.4 Implications for the
mobile radio operator
Where spectrum managers decide to make use of economic techniques,
there are important implications for the operators, both in the manner in
which they obtain a license and the manner in which they run their net-
work—for example, the use of technologies providing a high spectrum
efficiency becomes even more critical than it was before.
Some users are also caught between spectrum management policies.
Market forces are being used to assign their spectrum, but the spectrum
manager also wishes to place restrictions on the technology that they can
use in their spectrum. To date, there has been a tendency to mandate par-
ticular technologies in European countries where the use of GSM is man-
dated for cellular applications, TETRA for digital PMR, and the European
Radio Messaging Service (ERMES) for paging. Appendix B discusses
whether mandating technologies is appropriate and presents some argu-
ments that can be used if it is decided to attempt to challenge the mandate.
The use of the economic tools discussed in this chapter is almost cer-
tain to result in a higher cost to the operator than would have been the
case with more traditional spectrum management tools. Many operators
have complained that spectrum pricing and auctioning is just another
form of taxation that takes money out of the mobile radio industry and
increases the cost for consumers. However, the economic evidence is that
this is far from the truth. The early mobile radio operators typically made
supernormal profits, that is, profits in excess of the returns that could be
expected for the level of risk involved. Indeed, some of these early opera-
tors made around a 60% return on investment when the sector norm was
around 10%. Pricing will reduce these levels toward the norm, as during
an auction the rational operator will only bid at a level that still allows
them to make an adequate profit. Hence, mobile radio operators in the
future can expect to be profitable but not super-profitable, as long as they
bid sensibly for the spectrum. Clearly operators who overvalue the spec-
trum, as some of the PCS operators in the United States appear to have
done, run the risk of not being able to operate profitably. The positive side
is that the license award is now much more transparent, and rather than
spending time and money on lobbying activities often with an unsuccess-
ful outcome, companies now have a clear series of rules that they can fol-
low if they want a license.
290 The Complete Wireless Communications Professional
Bidding in an auction Many new operators will face an auction in
order to obtain their radio spectrum. It is quite likely that the complete
wireless professional will get involved in the process. In order to under-
stand how to devise an auction strategy and how to bid during an auction
it is first necessary to understand a little about auction design.
Auctions for radio spectrum are far from simple. Most people initially
think of an auction as the familiar bidding at an auctioneer’s for some
antique, but the auction forms used for spectrum distribution are vastly
more complex. Auction design itself is a complex field and there are chairs
in auction design within economics departments of some top universities.
In the simplest spectrum auctions, there is only one lot to be sold, for
example, a single national license to operate a mobile radio system. A
more complex auction might offer say two or three identical national
licenses and there might be a rule that each bidder can only obtain one
license. The next stage of complexity is that the licenses may not be iden-
tical, for example, in different frequency bands, and also where bidders
are allowed to obtain more than one lot. The final level of complexity is
where there are multiple lots both in different frequency bands and dif-
ferent geographical areas. Bidders might want to obtain two adjacent fre-
quency bands throughout the southern part of the country and may have
to win, say, 20 lots to achieve this. The last form is that closest to the PCS
auctions in the United States. Some of the different auction types that can
be used to overcome these problems are as follows:
◗English auction: In an English auction, a single item is offered and
bidders increase their offers until nobody wishes to bid more highly
than the last offer. It is important to understand with this auction
that the winner has not paid their own valuation of the item but
instead has paid slightly more than the second highest bidder’s
evaluation of the value of the item. This auction form is well known
but generally judged inappropriate for spectrum where sealed bids
are preferred. Without modification it cannot cope well with multi-
ple related lots.
◗Sealed bid first-price auction: In this auction, bidders submit a sealed
bid and the highest bidder pays what they bid. Bidders, however,
will not bid at their valuation of the lot but at a price that they esti-
mate is higher than what the other bidders will bid. If this estimate
is higher than what they are prepared to pay, then they will not bid.
Radio spectrum 291
Complexities then arise since all bidders are trying to second-guess
the other bidders. The result is often more of a lottery than other
auction methods.
◗Second-price sealed bid auction: In this auction, bidders submit a sealed
bid. The highest bidder pays the price offered by the second highest
bidder. This overcomes the problems of the sealed bid first price
since bidders now bid their full valuation. The problem with this
form of auction is that the public often perceives that the govern-
ment is “giving away” the spectrum for less than the bidders were
prepared to pay for it. This, of course, is not true, since the bidders
would not bid their full valuation if they knew they had to pay it,
but it is difficult to convince the public of the correctness of the auc-
tion. In New Zealand, public anger about the situation where there
were only two bidders—the first bid many millions, the second only
$1, and the first bidder was awarded the license for $1—resulted
in a ministerial resignation. Hence, this form of auction is now
rarely used.
There are a number of multiple object auctions that are complex and
only one has been used for radio spectrum. The single key type for radio
spectrum is the simultaneous multiple English auction. It was devised by
the FCC in 1994 and has been revised and updated in the light of a
number of auctions. For every lot to be sold, there is an unlimited number
of rounds using sealed bids. At the end of each round, the highest bid for
each lot is made public. For the next round, each bid must be above a
minimum increment over the previous bid price. All the lots remain open
until there is no bidding on any lot during a particular round. The advan-
tages of this form of auction are:
◗Bidders who want a number of related lots can make sure that they
obtain them since the bidding remains open until all lots have con-
cluded or can withdraw early when they realize that the bidding
will rise higher than their valuation (there is some risk that they will
have bid the highest price on one lot before realizing that the other
lots are too expensive and then have to withdraw from their “win-
ning” lot, incurring a financial penalty for doing so).
◗Bidders gain information about the value others place on the
license during the bidding process and can adjust their valuation if it
292 The Complete Wireless Communications Professional
appears out of line with that of others (e.g., if others appear to be
bidding much less, the bidder might conclude that they have been
optimistic about the risks).
◗Experience has shown that these auctions are effective in selling
similar lots for similar prices, allowing bidders to accumulate the
lots they require.
The full set of rules is necessarily very complex and includes rules
about timing, minimum increments, deposits, payments, and defaults,
for example. This complete rule set has been found to be necessary to pre-
vent bidders trying to find means to “cheat” the auction process.
Preparation for this form of auction by the bidder starts with their
valuation for the license. Valuation of the radio spectrum is a complicated
process but one that each bidder must carefully perform. Essentially, the
bidder builds a business case as explained in Section 8.2. The bidder then
decides what return on capital they require and any extra return they can
find is their valuation of the radio spectrum. Because building a business
case relies on difficult assumptions about subscriber numbers and tariff
predictions, it is not surprising that different prospective operators will
come up with different valuations. The basic bid strategy is then sim-
ple—continue raising your bids on each lot in which you are interested
until the valuation price is reached. However, if some lots are shaping up
more cheaply than others, then it may be appropriate to modify bidding
strategy in order to focus on a different geographical area or a different
frequency band. Actually bidding is more complex because of the need for
a computer to monitor all the different lots. Further, because the duration
of each round may be quite short (perhaps half an hour), it is necessary to
preplan different strategies, looking at a range of possible scenarios. Game
theory and “war game” preparation is a useful tactic here. Most bidders
will run bidding software on their computers that knows all the myriad of
rules so that they do not infringe upon any rules and can place bids in a
timely fashion. Bidding will normally be via the Internet using computers
to prevent all bidders having to be in the same building.
The U.S. PCS auctions have cast some doubt on the efficacy of this
auction form because many of the highest bidders have defaulted on their
bids and returned the spectrum to the government. This has caused many
to suggest that the auction form is flawed since it is failing to distribute
licenses quickly. This problem with auctions is well known and is called
Radio spectrum 293
the “winner’s curse.” Essentially, the winning bidder is the one who most
overvalues the market. When they come to implement their network,
their overvaluation becomes apparent and they may go bankrupt. This is
not problematic if the spectrum can be rapidly reclaimed and reauctioned
but is perceived by the public as a failure of the bid process. There are a
few rules that can be established to overcome the winner’s curse:
◗Require bidders to demonstrate that they already have funding to
finance their bid before they can make the bid.
◗Only accept bids from large companies with a good “track record” in
running networks (but this tends to reduce entrepreneurship).
◗Provide information as to the value of the licenses in similar situa-
tions (perhaps in other countries).
These will tend to reduce the dynamism in the bidders, and hence in
the manner in which networks are run, but will also reduce the risk of
defaulting. It is up to the governments to set an appropriate level of risk.
12.5 Government policy
Governments play a key role in the area of mobile and fixed communica-
tions. Most of the government regulators are generally concerned with
fixed operators [3]. Typically, they try to ensure that the incumbent fixed
operator, the PTO, does not abuse its monopoly position and indulge in
unfair competition. Fixed operators are generally outside the scope of this
book (except where they are also mobile operators), but a good descrip-
tion of the role of regulation on fixed operators can be found in [4].
There are a number of regulatory matters that impinge upon mobile
radio operation.
Coverage requirements Governments are typically keen that giving
out a mobile radio license results in the provision of mobile radio
services to most of the population. If, instead, a mobile radio opera-
tor decided to provide a service only in the capital city, which might be
a quite lucrative mode of operation, the government would be con-
cerned that mobile communications had not been provided to the whole
community and as a result the true economic benefit of the use of mobile
294 The Complete Wireless Communications Professional
communications would not be realized. In this instance, the government
would like a means to revoke the license and to give it to a different opera-
tor prepared to provide better coverage. The control that the government
uses over the mobile radio operator is typically a coverage requirement.
The mobile radio license will normally say that a certain percentage of the
population (often 90%) is covered within a given timespan (often 5
years). If this coverage is not met, then the government can withdraw the
license.
There is some debate as to whether coverage requirements are actu-
ally a useful tool for the government to adopt. To date, all mobile opera-
tors have surpassed their coverage requirements long before the date in
their contract as they have realized that good coverage is essential in win-
ning new customers. Further, if the operator decided that meeting the
coverage obligation would actually result in an unprofitable network,
they might be inclined to bid less for the license or not at all, reducing the
overall value of mobile communications. In a free market where there is
competition, it would seem that coverage obligations are not appropriate.
Finally, it is far from clear whether such obligations can actually be
enforced in any case. Say an operator had 80% coverage, rather than
90% (and measuring coverage to this accuracy is in itself a problem), then
it is unlikely that the government would withdraw the license since such
a move would result in many users being unable to use their mobile
phones, which would be unpopular.
Whatever the efficacy of coverage obligations, it seems likely that
they will be a part of mobile radio licenses for some time.
Fixed/mobile integration For some time regulators have differenti-
ated between fixed and mobile licenses. In particular, some fixed opera-
tors have been prohibited from holding mobile licenses in order to
increase competition. In some countries, the converse is also true, that
mobile operators have been prohibited from offering fixed services.
However, the distinction between fixed and mobile communications is
becoming increasingly slim. Fixed operators are now placing DECT base
stations at the end of fixed lines and claiming that this is just an extension
of the fixed service. Mobile operators are using their networks to provide
WLL connections, offering a fixed service. It seems likely that in the
future the regulator will increasingly be unable to draw a distinction
between fixed and mobile services and will stop attempting to make com-
panies provide only one or the other.
Radio spectrum 295
Number of mobile operators One of the key decisions that a regula-
tor needs to make is the number of mobile operators that should be
allowed. Coupled with this is a decision as to how much radio spectrum
each operator should be given. Although the limits of the radio spec-
trum place a maximum on the number of operators, this number is often
further restricted for competition purposes.
Selection of the number of operators is a very difficult problem. On
the one hand, if there are too many operators, too much will be invested
in infrastructure and communications will be expensive for the popula-
tion. On the other hand, if there are too few operators, then there may be
insufficient competition to drive prices down. This is a massively complex
situation in which engineers can do little to calculate the most appropri-
ate outcome. Experience has shown that two operators are probably
insufficient since a “cozy duopoly” tends to form. At present in most
countries where five have been tried, two have merged, resulting in four,
so the general assumption is that there should not be more than four. The
difficult question is then whether there should be three or four.
The complexity and importance of the situation can be seen by look-
ing at what recently happened in a European country. This country
already had two operators at 900 MHz and was forming a new law to
allow additional operators at 1,800 MHz. The initial position, apparently
formed without too much thought, was that there would be one addi-
tional operator at 1,800 MHz. This was borne out by the fact that there
was thought to be only sufficient radio spectrum for a single operator at
1,800 MHz, although more was becoming available later. However, when
the legislation to allow a single operator was placed before the govern-
ment, some objections were raised that more than one operator should be
licensed. In particular, EC law suggests that there are very few cases that
one operator should be licensed, with a shortage of spectrum being one of
the few allowable reasons.
At this point a team of technical and economic experts were called in.
The technical analysis attempted to establish how much spectrum would
be required. However, as shown in Chapter 2, a mobile radio network can
be built with limited spectrum if there are a sufficient number of cells.2
For the operator, there is a tradeoff between cost and spectrum. Hence,
the technical specialist rapidly concluded that from a technical viewpoint
296 The Complete Wireless Communications Professional
2. The minimum amount of spectrum is equal to the carrier bandwidth times the cluster
size. In the case of GSM, with a cluster size of 21 for the control carriers, this equates to
2×4.2 MHz.
there was actually sufficient spectrum for three operators; however,
they might not be able to operate economically due to the number of cell
sites required. The economic experts studied the situation and suggested
that appropriate auction methods could be devised to let the market
decide whether there should be one or two operators. Essentially, a form
of auction could be used where two licenses were initially offered and, if
there were not two appropriate bids for these licenses, the auction would
be rerun for a single license. The economists stated that this was the best
way to proceed since only the market had sufficient knowledge to judge
how many operators were required.
The government decided to ignore this advice and pressed ahead with
the legislation for a single operator. For a time this appeared to be suc-
ceeding, but in the final stages of legislation the legality of the move was
again questioned and it was finally judged to be inappropriate. At this
point, the draft legislation was withdrawn and replaced with legislation
that allowed two operators. Rather than just demonstrating a victory for
consultants over governments, this shows the regulatory difficulties in
determining how many mobile licenses should be awarded.
Distribution channels Another area where regulators can affect mobile
radio policy is in the manner in which operators are allowed to sell
their airtime to the public. In some countries the regulator has insisted
that operators should not be allowed to sell directly to the public but
instead should make use of service providers—third parties buying air-
time wholesale from the mobile operator and selling it through a chain of
stores to their customers. This clearly has an implication on the manner in
which the mobile operator is structured but has limited implications for
the engineering staff.
References
[1] NERA, Smith, Review and Update of 1995 Economic Impact Study, available from
the U.K. Radiocommunications Agency, 1997.
[2] NERA, Smith, Study into the Use of Spectrum Pricing, published by the U.K.
Radiocommunications Agency, Apr. 1996; also available from
http://www.open.gov.uk/radiocom.
Radio spectrum 297
[3] Calhoun, G., Wireless Access and the Local Telephone Network, Norwood, MA:
Artech House, 1992.
[4] Clarke, M., Networks and Telecommunications: Design and Operation, New York:
John Wiley, 1997.
298 The Complete Wireless Communications Professional
Standardization
The minute you read something you can’t
understand you can almost be sure it was
drawn up by a lawyer.
Will Rogers
13.1 Introduction
Standardization is becoming increasingly
important in the world of mobile radio. In cel-
lular, PMR, paging, and cordless telephony,
standardized products are starting to domi-
nate the world market. With standardiza-
tion of third generation products underway it
seems likely that the domination of standards
will continue into the foreseeable future. The
complete wireless professional may become
involved in standards in a number of different
ways:
◗Directly, as part of a team responsible for
writing a new standard or making amend-
ments to an existing standard;
299
Contents
13.1 Introduction
13.2 Standards-
making bodies
13.3 Writing
standards
13
CHAPTER
◗Indirectly, as the ongoing standardization affects product strategy;
◗As an end user of the standard, either in an operator or a manufac-
turer, trying to understand a published standard and develop an
appropriate offering based on the standard.
In all these cases it is helpful to understand the role of standardization
bodies, the manner in which mobile radio standards are written, and the
choices made during standardization. This chapter describes the stan-
dardization process in general and presents a case study of a particular
standardization exercise to illustrate some of the key issues.
13.2 Standards-making bodies
Standards-making activities occur in three key places around the world:
Europe, the United States, and Japan. In Europe, standards are developed
by the ETSI; in the United States, in the main by the TIA; and in Japan by
the Association of Radio Industries and Businesses (ARIB). The most successful
of these bodies have been ETSI and the TIA, and this section will focus on
these two.
ETSI ETSI is based in France but is responsible, under the auspices of
the EC and CEPT, for the development for all mobile radio standards for
Europe. A simplified diagram of the structure of ETSI is shown in
Figure 13.1. As can be seen, ETSI covers the standardization of all tele-
communications equipment including fixed and mobile equipment. Each
different area tends to have its own technical committee (TC) that, when a
particular standard is being developed, tends to be given its own working
team of individuals who work full time at ETSI on the standard for the few
years that its development takes. The key cellular standardization takes
place within the special mobile group (SMG). This does not follow the same
naming convention as the rest of the development groups since SMG was
originally formed within the CEPT and was then “transferred” across to
ETSI during the development process of GSM (which takes its original
name of Group Special Mobile from the committee performing its stan-
dardization).
Within SMG there are a number of subgroups that change on a regu-
lar basis, but the key subgroups are:
300 The Complete Wireless Communications Professional
◗SMG1—User requirements: This group captures the user’s needs
and sets them out in clear documents known as requirement
documents.
◗SMG2—Radio aspects: This group studies issues associated with radio
transmission and writes the associated standards.
◗SMG3—Network aspects: This group designs the protocols required
for correct operation of the network.
◗SMG4—Data systems: This group considers issues particular to data
transmission.
◗Numerous other groups considering aspects such as SIM cards and
testing.
Work within ETSI tends to start when the EC notes the requirement
for a new standard. The EC will request ETSI to identify the required
resources and set up a project team (PT) for the duration of the standardiza-
tion process. The project team is staffed by engineers on secondment from
industry, paid for by the EC, for the duration of the standardization. For
Standardization 301
General Assembly
ETSI Board Finance Committee
Technical committees Project teams Support teams
Network
aspects
Signaling
protocols
Many other
teams
Special
mobile group
TETRA
Security
algorithms
User
groups
Many other
teams Many other
teams
Figure 13.1 The structure of ETSI in 1998.
the major standards the funded work can run to thousands of man-days
of paid activities costing many millions of pounds. Industry is then invited
to partake in the standards process. Only European companies can belong
to ETSI, although U.S. companies such as Motorola qualify as a result of
their European activities. Typically, monthly meetings are held by each
group at which all interested parties attend, documents are presented,
and key decisions are taken by consensus, or by voting if required. This
process is described in more detail in the next section.
ETSI standards are published and are available to ETSI members from
the ETSI document center. Once they have been officially approved by
ETSI, they typically become mandatory for that particular technology
within the EC (see Appendix B for more details of mandating standards).
More details about ETSI can be obtained from [1].
U.S. standards bodies There are two bodies in the United States
involved in standardization. Most mobile standardization is performed by
the TIA; however, the Alliance for Telecommunications Industry Solutions
(ATIS) also plays a role. Historically, standards making in the United
States was performed by AT&T, then the only organization with an inter-
est in telecommunications standards. As the industry was liberalized,
trade bodies became more important. The TIA took over most of the stan-
dardization of wireless systems, whereas ATIS looked after wireline
standardization. However, during the PCS auctions, the T1 committee of
ATIS took responsibility for standardization of the GSM1900 solution
within a group known as T1P1. This group performed the minor modifi-
cations on the GSM standard required for North American operation.
Nevertheless, the bulk of the mobile standardization work is performed
within the TIA, which is now examined in more detail.
The TIA has five product-oriented divisions, namely:
◗User premises equipment;
◗Network equipment;
◗Wireless communications;
◗Fiber optics;
◗Satellite communications.
These address the legislative and regulatory concerns of the product
manufacturers and prepare standards dealing with performance testing
302 The Complete Wireless Communications Professional
and compatibility. TIA is accredited by the American National Standards
Institute (ANSI). It tends to firstly give standards interim status (IS) and
then, after appropriate testing, full ANSI accreditation.
Within the wireless communications division there are three
subdivisions:
1. TR-8, which develops mobile and personal private radio stan-
dards for PMR usage;
2. TR-45, which develops public mobile and personal communica-
tions systems standards;
3. TR-46, which develops mobile and personal communications
standards for the 1,900-MHz band.
In practice, TR-46 now performs little work, with the key cellu-
lar standardization being performed in TR-45. TR-45 is subdivided as
follows:
◗TR-45.1 deals with the analog standards AMPS and N-AMPS.
◗TR-45.2 deals with the intersystem interface know as IS-41 (the
equivalent of the MAP interface within GSM).
◗TR-45.3 deals with D-AMPS, also know as IS-136.
◗TR-45.4 deals with the “A” interface that connects base stations to
switches.
◗TR-45.5 deals with cdmaOne.
◗TR-45.6 deals with the emerging cellular packet data system.
U.S. standardization is somewhat different from that in Europe. The
standards bodies have no permanent staff who can be assigned to a proj-
ect team to progress a particular standard—all members are part-time
attendees from their companies. As a result, standardization tends to be
slower and it is often more difficult to achieve consensus than within
ETSI. In practice, most standards get developed in a quite different man-
ner. A company with a good idea will persuade a number of other compa-
nies to form an ad-hoc group that sits outside any standards bodies. This
group will develop a specification and design that they will then present
to the TIA in almost finished form. If there is sufficient weight behind the
Standardization 303
proposal, it will be accepted and a new division within TR-45 will be
established to develop the proposal. The determination of “sufficient
weight” is an inexact science that depends more on politics than on quan-
titative measures of support. This use of ad-hoc bodies means that there
can often be more than one standard for the same area, such as both the
D-AMPS and cdmaOne standards for digital cellular. Such an approach
would not be allowed within ETSI, where one of the objectives is a single
unifying standard.
Because of the major differences in the manner in which standards
are developed, the European and U.S. ways have quite different charac-
teristics. The European way has the advantage that any standards pro-
duced are typically highly tested, unlikely to have significant errors, and
generally carefully designed to meet the perceived requirements of the
users. In contrast, U.S. standards may be developed without considera-
tion of the user’s needs and may achieve standardization before compre-
hensive testing. However, the European way allows only one standard to
be designed in one particular manner. Contributors who disagree with
the standardization work can make objections, but if these are overruled
by the committee there is little that they can do. The U.S. method allows
those unhappy with one particular standardization route, such as Qual-
comm, to embark on a parallel route in a manner that appears to some to
be more democratic. In general, Europe is providing the world’s most
popular standards, generally due to their careful design and their support
by the majority of the world’s leading manufacturers. However, without
the U.S. approach to standardization, it is unlikely that there would be a
CDMA-based cellular standards available to date.
More information about the TIA can be found at [2] and about the T1
committee of ATIS at [3].
13.3 Writing standards
The writing of standards is quite different from almost any other engi-
neering discipline and something that takes some getting used to. An ETSI
standard is normally divided into three stages:
1. The first stage is a requirements specification that sets out the
requirements on the item being standardized.
304 The Complete Wireless Communications Professional
2. The second stage is a logical description of the manner in which
the item will be designed without being specific to any particular
realization—for example, it might suggest that group calls should
be achieved by having one shared channel in each cell.
3. The third stage is the production of the final standards docu-
ment; this stage normally lasts much longer than the first two
stages.
In principle, each of these stages should be completed before the next
stage starts. In practice, the first stage is typically only partially complete
before the second stage starts. As implementation problems are discov-
ered in the second stage, these may be fed back to the first stage commit-
tee who may agree to alter the requirements if they are likely to be unduly
expensive to provide. The same developments might happen between the
second and third stages. Only as all the stages are coming close to comple-
tion are the early stages likely to be frozen.
The process of writing documents by committee is an interesting one.
Typically there will be a special committee established as an offshoot from
one of the permanent committees that will be responsible for developing
the standard. This committee will have three parts corresponding to each
of the three phases of standardization. Each of these parts will meet,
probably on a monthly basis. At the meeting, the first activity is to number
and organize the input documents. Document control is essential in stan-
dardization bodies where otherwise matters can quickly get out of hand.
The documents are then assigned to agenda items. As the meeting pro-
gresses through the agenda, each person who has provided an input
document is asked to present his or her document. This typically means
summarizing the document verbally and drawing the attention on the
delegates to the key points in the document. There will then follow a
period of discussion on the document during which the other delegates
will attempt to find problems with the document. The author will take
note of these comments and revise the document accordingly, either for
input on the next day of the meeting or at the next meeting.
A volunteer is normally appointed to be editor of the specification.
This person is responsible for keeping the latest version of the specifica-
tion, for presenting it at each meeting, and for revising it in line with com-
ments. Others at the meeting may provide additional text for the standard
in their input documents and, if it is agreed upon, will pass this text to the
Standardization 305
editor for inclusion in the specification. There are strict editorial guide-
lines for the format of specifications and the manner in which revisions to
the specification are made.
This process works well while there is always someone who is willing
to provide an input document in all the areas where input is required and
no two people are working on the same input document. In practice, the
problem of nobody providing a document on a particular area is generally
solved as delegates become aware that a lack of document will slow the
standardization and eventually agree to take on the work to prevent
deadlines slipping. The problem of more than one input document on the
same area is more difficult to solve, but one that happens frequently. Dif-
ferent individuals will often have different ideas on the way that a par-
ticular problem is best solved. Both will produce input documents with
different solutions that they will present. The rest of the committee will
assess the different documents and, through their comments, will indi-
cate their preference for one or the other. Because it is a standards com-
mittee, a decision has to be made democratically, and in some cases a
formal vote will be taken on which of the different inputs should be used.
In practice, matters rarely come to a vote. Those writing the input docu-
ments will realize from the comments and from the discussion in coffee
breaks whether their ideas find much favor and will tend to withdraw
unpopular suggestions before a vote is reached. Seemingly intractable
arguments do arise from time to time, and the normal approach is to then
refer the problem to the permanent committee who can judge the most
appropriate solution.
The advantages of such a process are that it is truly open, democratic,
and the process of peer review and criticism generally results in a standard
with fewer errors than might otherwise have been the case. The disad-
vantage is that standardization in this manner is very slow, with work
only really progressing once a month and in a costly manner to the parties
involved who continually send key engineers to meetings all across
Europe. Matters are sometimes made worse when large manufacturers
send new engineers to ETSI meetings as part of their training, particularly
on the GSM standard. Time is then required in the meetings to explain
some of the more complex points of the standard to these new delegates.
This can occur at almost every meeting.
When actually authoring a particular input document, the author
needs to use very precise and terse language. If the text is to form part of
306 The Complete Wireless Communications Professional
the final standard, it must be completely clear and unambiguous. For
example, in English the words should, might, may, and could are all ambigu-
ous—it is not clear whether a particular action is required or not required.
ETSI guidelines mandate the use of shall to indicate that a particular
action must be performed and may to indicate that performance of a par-
ticular action is optional. For the stage-one standards, the text may read
like a normal document. By the stage-two standard it is already becoming
terse but might, in some cases, offer some explanation as to why certain
options have been selected. By stage three, the specification reads a little
like a computer program with no comments, showing only the actions
that the mobile and the network must take in a range of different
situations.
As a result, reading specifications is extremely hard work. To under-
stand the functioning of GSM purely from reading the specifications
would be nearly impossible, which is why there is a thriving industry
writing books that effectively decode the specification documents.
References
[1] ETSI website is at http://www.etsi.fr.
[2] TIA website is at www.tiaonline.org.
[3] T1 committee of ATIS website is at www.t1.org.
Standardization 307
Becoming a better
wireless professional
Acomplete wireless professional needs to
be a well-rounded individual. In addi-
tion to having a good understanding of the
underlying concepts, the complete wireless
professional will need to handle issues of con-
flict in a competent and professional manner,
have a good understanding of management,
and conduct his or her career in a manner
that will enhance his or her ability to provide
good engineering advice. This part looks at
how to become a better wireless professional.
V
PART
Areas of conflict
The most savage controversies are those
about matters as to which there is no good
evidence either way.
Bertrand Russell
14.1 Introduction
Conflict has been a consistent feature of
the world of mobile radio in recent years.
A wireless professional is almost certain to
become involved in some form of conflict
in his or her career, and the better ones
will frequently tend to be involved as they
get brought into the front line as “elite
troops.”
Conflicting situations are almost always
due to different manufacturers trying to
establish their preferred technology in order
to sell more product and increase profitabil-
ity. What almost invariably happens is that
the two warring parties both claim that their
product is the best, often for the same
reasons. When mobile radio systems were
311
Contents
14.1 Introduction
14.2 TETRA versus
GSM
14.3 DECT versus
PHS
14.4 CDMA versus
TDMA
14.5 Handling conflict
14
CHAPTER
simpler, it might have been possible to resolve these conflicts in a straight-
forward manner, but mobile radio systems have become sufficiently com-
plicated that typically the conflicts cannot be solved by a rigorous
mathematical analysis or simulation. The net result is that both sides can
continue to make claims, supported by their own, favorable, analysis,
which independent arbitrators (of whom there are very few) are unable
to disprove.
These conflicts have become increasingly intractable and the engi-
neers involved in them have tended not to behave in a manner most
fitting to their profession. The complete wireless professional should
understand how to behave in a situation of conflict and how to act in such
a manner that the best interests of all concerned can be realized. It is
important to remember the following points:
◗In an argument where certain technical parameters cannot be cal-
culated accurately, it is often better to say this than to use approxi-
mations that cannot be universally accepted.
◗Bitter propaganda battles seem to do neither side any favors. Using
different tactics may be more appropriate.
◗It is actually quite rare for the best technical solution to be the that
which is accepted. A good example of this is the VHS versus Beta-
max battle. Often, other economic and market-related factors are
more important than engineering issues.
◗Many conflicts are not actually about technical matters, however it
may seem, but are about patents, intellectual property rights, poli-
tics, and market position.
To illustrate some of the issues involved, a few of the most prominent
conflicts in recent years are considered in more detail here. What will
become apparent is that it is rarely possible to provide a clear-cut solution
to the conflict but that careful analysis can reveal the key issues. The con-
flicts considered are:
◗TETRA versus GSM;
◗PHS versus DECT;
◗CDMA versus TDMA.
312 The Complete Wireless Communications Professional
14.2 TETRA versus GSM
14.2.1 Background to the debate
As discussed in Chapter 4, TETRA is the new European standard for
advanced PMR applications. During its design it was intended to be
used by all major PMR users and by many of the smaller scale users.
Three manufacturers in particular—Motorola, Nokia, and Philips (now
SiMoCo)—invested substantial effort in developing the standard and in
product design. However, during the standardization work, the Interna-
tional Railway body, the UIC, made the decision that its next mobile radio
system would be based on GSM rather than TETRA and initiated the stan-
dardization work to add PMR features to the GSM standard. As a result of
this, other PMR users were faced with a choice as to whether to adopt
TETRA or GSM. TETRA manufacturers were horrified by the possibility
that their marketplace might be suddenly reduced and campaigned vocif-
erously to demonstrate why GSM could not possibly meet the needs of
PMR users. Meanwhile, the UIC and some of the GSM manufacturers
were keen that other PMR users adopt GSM in order to spread the cost of
the necessary modifications over a number of other users. The result was
conflict.
14.2.2 Evaluation of the technologies
The TETRA standard was conceived to provide a European-wide standard
digital PMR technology, with the associated benefits of open sourcing,
economies of scale, and roaming possibilities. GSM was conceived to pro-
vide public cellular communications. However, the European railways
decided to select GSM rather than TETRA as their standard because at the
time there was a lower risk associated with GSM, it met their timescales,
and GSM’s enhanced roaming capabilities compared to TETRA were
judged to be an important feature for high-speed international trains.
In addition, there are a number of proprietary digital PMR products
from companies such as Ericsson, Matra, and Motorola and a U.S. stan-
dard called APCO25, discussed in Chapter 4. These could offer an alterna-
tive to TETRA or GSM but do not provide the multisourcing capabilities
that generally make open standards so attractive. Further, government
bodies will be under some pressure under EC procurement law to procure
Areas of conflict 313
an open standard for their radio system that may remove the choice of
proprietary systems for some users in this area. For these reasons proprie-
tary systems will not be considered further here.
When looking at the functions of GSM and TETRA, what is apparent
is that both standards largely meet the major needs of all user groups.
Both will support a wide range of voice and data capabilities. TETRA has a
number of additional features over GSM-ASCI, which are:
◗Back-to-back operation and repeater operations with one mobile
inside a coverage area able to relay the signal to a mobile outside the
coverage area; direct-mode facilities are not envisaged within GSM,
with dual-mode mobiles providing the only feasible direct-mode
option;
◗Ambient listening (the ability for a controller to activate a mobile
without intervention from the user so the controller can listen in
the case of hijacks and similar incidents);
◗Pseudo-open channel where a user group can withdraw certain
specific radio channels from the pool of channels available to all
users to provide a minimum guaranteed level of service to impor-
tant users;
◗Load apportionment so that in overloaded situations each user
group gets a fair share of the resources;
◗Barring of direct access to certain types of calls and so insisting they
are routed through the dispatcher;
◗Dynamic group allocation where groups can be created by a dis-
patcher very quickly for a particular incident—the ASCI features
only allow fixed group allocation.
In essence, GSM is better at wide area coverage, roaming, interna-
tional operations, billing, and network management—everything one
might expect from a cellular system. TETRA is better at flexible deploy-
ment in both small and large configurations and a range of services
mainly targeted at the emergency services.
There is some risk that TETRA will not have all the facilities promised
when it first arrives; the number of data services was recently dramati-
cally cut during the standardization process, and some manufacturers are
seeking reduced functionality TETRA equipment in order to minimize
314 The Complete Wireless Communications Professional
their risk, while the number of GSM services is ever-increasing. Equally,
there is some risk that the GSM ASCI features will not be widely
implemented.
TETRA requires a smaller bandwidth than GSM for voice communi-
cations. TETRA systems can provide 4 voice channels in 25 kHz (6.25 kHz
per channel) whereas GSM currently provides 8 voice channels in
200 kHz (25 kHz per channel) and will change to 16 voice channels
in 200 kHz (12.5 kHz per channel) with the imminent introduction of the
half-rate codec.1However, it is important to consider the relative cluster
size of the two systems. The GSM specifications show that it requires a
carrier-to-interference (C/I) ratio of 9 dB, whereas the TETRA specifications
show a C/Iratio of 18 dB. According to Lee [1] the cluster size is given by
KSIR=⋅
23(14.1)
Hence, it can be calculated that the (theoretical) minimum cluster sizes
for GSM and TETRA are 2.3 and 6.5, respectively. Taking these factors
into account, the full-rate GSM coder provides up to 17 voice channels
per cell per megahertz, the half-rate GSM coder provides 34 voice chan-
nels per cell per megahertz, and TETRA provides 24 voice channels per
cell per megahertz. Given that most GSM operators tend to deploy the
full-rate coder, TETRA provides a gain of around 40% in spectrum effi-
ciency. This improvement in bandwidth efficiency offered by TETRA
could be extremely important for users who are in a spectrum-limited
situation.
Despite the additional functionality offered by TETRA, for many users
cost will be the overriding consideration. Economic issues are considered
in more detail in the next section.
14.2.3 Economic comparison
Once TETRA is available and well established to the extent that analog
PMR use is rapidly decreasing, a PMR user might face the following
alternatives:
Areas of conflict 315
1. Although most public GSM operators are not planning to deploy the half-rate coder
because of its perceived low voice quality, voice quality is less important to PMR users
who may prefer the high-spectrum efficiency that results.
1. Self-provide its own PMR system based on TETRA (or potentially
a proprietary technology);
2. Move to a shared (PAMR) system based on TETRA;
3. Self-provide its own GSM system;
4. Move to a public cellular GSM system.
The basic problem with GSM for private users is that it was
not designed for small-scale deployment. Recently manufacturers have
announced systems designed for only 10,000 users, which represents a
reduction over previous figures of 100,000 users but is still excessive for
most private users. Each cell provides a minimum of 7 voice channels
(15 with the half-rate codec) and the smallest deployment requires about
2×4.2 MHz of spectrum.2Unless this sort of capacity is required, GSM will
be extremely uncompetitively priced for the private user. Only organiza-
tions such as the railways and the police could realistically consider oper-
ating their own GSM system.
When comparing the choice between self-ownership of TETRA and
GSM (options 1 and 3, respectively) a number of issues are relevant. Cost
is clearly important, and the relative costs of the two systems depends on
the coverage and capacity required, with GSM generally being favored
where high levels of capacity (typically above 4 channels per cell) are nec-
essary. Functionality is also important and some user groups will select
one of the two systems because it offers the particular facilities they
require. In this area there have been conflicting choices with the railways
selecting GSM, the U.K. Home Office indicating a preference for TETRA,
the French Police choosing a proprietary system called TETRAPOL built
by Matra, and the Basque police selecting GSM!
For most users, self-provision of a GSM system (option 3) is not
a feasible possibility. Of the remaining three options, the use of shared
PAMR or cellular systems (options 2 and 4) depends first on the exis-
tence of appropriate networks and then heavily on the tariffs set by the
operators.
Regarding the potential of shared TETRA system, a number of national
PAMR operators have signed the TETRA memorandum of understanding
316 The Complete Wireless Communications Professional
2. Based on one carrier per cell with a 21-cell repeat pattern for the control channels.
(MoU) suggesting they have some interest in this area. In addition, there
are the changes likely to be brought about by the private finance initiative
(PFI) in the United Kingdom and similar initiatives in other countries. In
essence, this seeks to encourage the private sector to provide infrastruc-
ture and supply services to the public sector. This is the basis on which the
U.K. Home Office is currently working with its public safety radio communi-
cations project (PSRCP). The result of such initiatives is that users who his-
torically have owned and operated their own radio system are
considering sharing systems with others. Either of these may lead to a
shared TETRA system.
Concerning the GSM operators, some are clearly interested in attract-
ing PMR users onto their network, first through a modified tariff and then
at a later stage through the addition of the required functionality. While
the provision of appropriate tariffs without any additional features may
be attractive to some PMR users, current GSM networks lack many of the
features that many PMR users would find essential—in outline, the ASCI
features. Without these features, the attractiveness of any GSM offering
would be significantly reduced.
If we assume that shared TETRA networks and attractive PMR offer-
ings from cellular operators do emerge, then the smaller users will face a
three-way choice between options 1, 2, and 4. In the instance where they
only require coverage of a small area such as a single site but generate a
great deal of traffic within that area, self-provision using TETRA is likely
to be the most attractive alternative (option 1). Because of the likely cost
increase of TETRA over current analog systems, the threshold traffic level
where self-provision is economic is likely to rise from the present level
with the result that some current PMR users will find it more economical
to move to a shared system.
If coverage over a large area is required, then shared systems are likely
to be more appropriate. Whether this is TETRA or GSM will depend on
cost and functionality. It is too early to say at this stage what the relative
costs will be. While the GSM cellular operators do not need to build a net-
work from scratch, they will be restricted in the tariffs they offer if they do
not wish to cause migration of existing users. Early estimates are that
GSM systems may offer lower cost but also lower functionality. This
should become more apparent in the next few of years.
For the larger users, the choice between shared and self-provided sys-
tems depends upon many factors. In the case of government bodies, the
Areas of conflict 317
PSRCP is likely to force a move to shared networks. In the case of bodies
such as the railways, estimations of traffic levels will allow the compari-
son of tariffed costs against the cost of ownership to be performed.
14.2.4 Analyzing the debate
Looking at the facts presented in the preceding analysis and assuming that
these provide a fair representation of the situation, it would appear that
the key issues and uncertainties are the following:
◗TETRA will apparently provide a greater functionality than GSM,
but it is not clear to what extent this functionality will be valued by
users. Certainly some users will value it more than others.
◗TETRA may provide a greater spectrum efficiency than GSM, but
this remains to be proven and it is not clear to what extent this is an
issue for the potential users.
◗TETRA will probably be more expensive than GSM for most deploy-
ments, but there will remain situations where the converse is true.
◗The optimum choice for both systems depends on manufacturers
providing the technology with all the features present and opera-
tors deploying the technology.
◗There are many confusing issues and unknowns such as the new
funding process in use by some public bodies that may further cloud
the issue.
How is the complete wireless professional to make sense of all these
arguments? Many of those involved in the debate could see little further
than the argument about functionality, pointing out that since TETRA
had better functionality it was the best choice. However, decisions as to
which radio system to adopt are now generally made on an economic
basis, looking at whether a more expensive system will provide benefits
sufficient to offset its increased price. With further analysis, it became
clear that for most of the users, the additional features offered by TETRA
did not have much value attached to them and hence the argument about
additional functionality was false. The key exception to this was the police
who, it appeared, did value the additional functionality sufficiently to pay
more for the technology.
318 The Complete Wireless Communications Professional
The complete wireless professional would have noted by this point
that, in fact, the engineering issues are not the key points at stake here.
Also, he or she will have noticed that many of the issues depend on the
situation—for example, airports are in a quite different situation to taxis
and, hence, it is not possible to provide any general answers to the debate.
Further, the outcome is dependent on the strategy of manufacturers and
operators. Typically, it is not possible to predict the strategy that manufac-
turers and operators will adopt, and long-held strategies can be changed
overnight. For example, if no cellular operator announced that they were
to offer the ASCI features, then the debate as to whether TETRA or GSM
was more appropriate would change dramatically overnight.
The complete wireless professional would be very wary of taking sides
in this situation. The engineering issues can be stated with some certainty,
but it is not these issues that will drive the selection. Much will depend on
forces outside the control of the engineer who would do well to provide a
solution of the form “If xthen y, but if not xthen z.” The engineer should
also seek the support of the finance and strategy departments to develop
a detailed engineering case and cost-benefit analysis and to understand
any strategic implications. Armed with these tools, the decision should
become more straightforward.
14.3 DECT versus PHS
14.3.1 Background to the debate
The two cordless technologies of DECT and PHS were introduced in
Chapter 5. Most major manufacturers have decided to make one of these
two products, but not both. Typically, the European manufacturers have
selected DECT, while the far-Eastern manufacturers have selected PHS.
Both sets of manufacturers have formed groupings typically called MoU
groups that they have used to attack the other party. As always, the
debate has become vociferous.
14.3.2 The key issues
Different manufacturers have made different claims as shown in
Table 14.1.
Areas of conflict 319
Table 14.1
Claims Concerning DECT and PHS
Characteristic Ericsson [2] Fujitsu [3]
Capacity DECT 30% greater than PHS PHS is greater than DECT
Cost DECT less than PHS PHS is less than DECT
Planning DECT easier than PHS —
Data rate DECT can provide ISDN
whereas PHS cannot
—
Repeaters Can be provided by DECT but
not PHS
—
Interworking with GSM DECT can achieve this but not
PHS
—
Delay — PHS is lower than DECT
PSTN connection — PHS is simpler than DECT
Power consumption — PHS is lower than DECT
Compared to the previous conflict, this would appear to be one that
can be resolved more readily by engineering analysis alone. Below, each
of these points are addressed in the order in which they are raised.
Capacity DECT provides 12 traffic channels per 2-MHz bandwidth,
that is, 6 per megahertz; while PHS provides 4 traffic channels per
300-kHz bandwidth, that is, 13 per megahertz. However, PHS requires
around 3 dB more cochannel protection as a result of its more complex
modulation scheme, increasing the cluster size that must be used. The
effect of this on the cluster size can be modeled as follows. Making use
again of Lee’s equation, the cluster size of DECT, with an SIR of around
9 dB will be 2.3, whereas that for PHS witha3dBgreater SIR requirement
will be 3.2. Factoring this into the capacity results in a DECT capacity per
cell of 2.6 voice channels/cell/MHz, while PHS achieves 4 voice chan-
nels/cell/MHz. Hence, it would appear that PHS can provide a greater
capacity per megahertz per cell. However, it is not clear whether this is an
important issue.
Infrastructure cost It is not generally possible to evaluate the relative
infrastructure costs until quotations from the manufacturers have been
received. Because fewer DECT transceivers are required since each DECT
transceiver can provide 12 channels compared to the 4 of PHS, it may be
that economies can be realized in the manufacturing, which will cause
DECT to be cheaper. However, in the case that only 4 channels are
320 The Complete Wireless Communications Professional
required, the DECT system will probably be more expensive. In practice,
the base station costs will be dominated by the economies of scale
achieved and not the manufacturing difficulties. Moreover, in this area, it
remains to be seen which technology will achieve the greatest economies.
This would appear to be an issue that cannot yet be resolved and depends
on the deployment, but where high capacity is required, the greater
number of channels on a DECT transceiver would make it likely that
DECT would be less expensive.
Simplicity of planning Since both systems use DCA, in most deploy-
ments it would seem likely that there is little difference between the two
systems. The only slight difference is that PHS requires separate control
channels whereas DECT uses the same frequencies for control and traffic
channels; as a result, DECT may be slightly simpler to plan.
Provision of 64-kbps bearers It is clearly correct that DECT, with its
capability to concatenate channels, can provide higher data rates than
PHS. Concatenation of channels will probably be introduced to PHS at
some point, but the lower number of bearers per channels means that
PHS will always be inferior to DECT in this area.
Provision of repeaters Although there may be repeaters in the DECT
product range and not in the PHS range, there seems little reason why
PHS repeaters could not be provided if required.
Interworking with GSM The only reason why DECT has an advan-
tage in this area is because standardization has been taking place for some
time. If required, PHS could also be made to interwork with GSM,
although there may be political difficulties in writing the standards since
ETSI is unlikely to welcome the non-European standard.
Delay, connection, and power consumption The specifications
show that PHS has a shorter delay than DECT. However, in both cases
the delay is insignificant. Both are probably simple to connect to the
PSTN and the level of power consumption is unlikely to differ much
between them.
14.3.3 Analyzing the debate
In this case, most of the issues can be resolved by engineering analysis,
although probably neither of the two parties would agree fully with the
Areas of conflict 321
preceding analysis, and further study may be more appropriate in some
areas. Nevertheless, it seems clear that PHS provides a higher capacity
while DECT provides a wider range of services. The major unknown is the
relative costs between the two systems. As previously mentioned, since
most network decisions are taken on a cost basis, the decisions are diffi-
cult to resolve in general. However, in specific cases, with quotes from
manufacturers and a network plan, it becomes entirely tractable to
resolve the issue.
The complete wireless professional would determine whether capac-
ity or functionality was of overriding importance in this deployment,
determine the cost differences between the two systems, and make an
informed decision as to the most appropriate choice. Typically, with cord-
less systems, capacity, although important, is not critical because of the
inherently high-capacity nature of the deployment (although this is not
the case for WLL systems where cordless cells are larger). Functionality
may be critical for certain deployments where marketing requires a par-
ticular facility and this should be established. Again, the complete wire-
less professional will make a decision mostly based on financial rather
than technical issues.
14.4 CDMA versus TDMA
14.4.1 Background to the debate
The two cellular systems, GSM and cdmaOne, were introduced in
Chapter 3. What was not mentioned was the bitter debate that has taken
place between the manufacturers of the two different technologies. The
history started around 1991, when a relatively small U.S. company,
Qualcomm, announced that it had designed a new mobile radio system
based on CDMA technology that offered substantial capacity gains over
existing systems. Qualcomm made dramatic claims for their technology,
stating that it could provide a capacity over 20 times greater than the
existing U.S. AMPS analog technology. Obviously, if true, this was good
news for operators and for Qualcomm, but bad news for manufacturers
who had invested heavily in GSM, especially as Qualcomm made it clear
that they held all the key patents required for their CDMA system.
322 The Complete Wireless Communications Professional
A parallel debate took place in the United States between cdmaOne
and IS-136. In this case the protagonists were Ericsson for IS-136 and
Qualcomm for cdmaOne. The debate was very similar to the GSM–cdma-
One debate and is not discussed further in this section.
At first engineers attempted a mathematical analysis and an analysis
using simulation to determine whether these claims were correct. How-
ever, although both approaches could be used, they required major sim-
plifications that were soon challenged as being unreasonable. Qualcomm
took a high-profile approach to tell everyone how good their technology
was compared to other technologies which led the GSM manufacturers to
attack their claims. The resulting “battle” was a little pointless because it
was clear that the answer would not be known until CDMA systems were
deployed on a large scale. Nevertheless, it was important to convince a
number of operators to do this, and so the “marketing” continued from
both sides.
14.4.2 The capacity of CDMA versus
TDMA
TDMA and CDMA are both ways of dividing up the radio spectrum so that
a number of users can talk at the same time. There are two key issues. The
first is the efficiency of the division process taking into account guard
bands that need to be provided between adjacent users to stop them inter-
fering. The second factor is the capability of the access method to
distribute the interference evenly across all mobiles, as mentioned in
Section 2.4.8. Only if the interference is evenly distributed across all the
mobiles can the minimum cluster size be adopted and the maximum
capacity achieved.
When comparing CDMA and TDMA systems, it is important to assess:
◗How much spectrum is lost in the process of division of the
frequencies?
◗How successful is the access method in distributing interference
evenly across all the users?
Division of the frequencies Inefficiencies in TDMA result for sev-
eral reasons.
Areas of conflict 323
◗As discussed in Section 2.4.8, there is a need to allow mobiles time
to increase their power at the start of the burst.
◗Because of the high bandwidth used, ISI becomes problematic and
space needs to be set aside for a sounding sequence for the
equalizer.
◗Framing information is required by the mobiles so that they are able
to transmit in the correct place.
Of these, the first two are most important. As seen in Section 3.2, in a
typical burst of 148 data bits, only 116 can be used to transmit user’s data,
representing an efficiency of only 78%.
In CDMA, the inefficiency is caused by signals not being received with
equal power and hence interfering to a larger extent with other users,
reducing the capacity. As shown in Section 2.4.8, with a relatively small
error in power control, the system capacity might fall to only 40% of what
it would be with perfect power control, although this is something that
needs to be proved in actual deployments.
Distributing the interference Because in CDMA all mobiles use the
same frequencies, they interfere with each other to the same extent. As a
result, CDMA perfectly distributes interference between users.
TDMA inherently results in uneven interference since some users on
the same timeslot will be closer than other users and, hence, will experi-
ence unequal interference. As a result, the CDMA cluster size is around
one-tenth that of a typical TDMA system. The GSM cluster size can be
reduced using some of the techniques described in Section 9.4, which can
reduce the gains of CDMA, but this simple analysis suggests that, taking
the detrimental effects of power control and the positive effects of inter-
ference distribution, CDMA might have a capacity gain of around 2 to
4 times that of GSM.
The complete wireless professional, realizing that a mathematical or
simulation approach is intractable, would highlight the key issues and
realize that CDMA will typically have a higher capacity than TDMA, with
the extent of the advantage depending on the way that both of the net-
works are deployed and the capacity enhancement techniques adopted
within GSM. He or she would wait until networks had been deployed, if
possible, to look at the practical evidence, which appears to show that
324 The Complete Wireless Communications Professional
CDMA typically provides a capacity gain of approximately two to three
times that of GSM.
14.4.3 Other issues introduced into
the debate
Although the debate tended to focus around which system had the great-
est capacity, there were a number of other factors that were also claimed
to be important. These included claims that:
◗CDMA systems have a greater range than GSM.
◗CDMA does not need frequency planning and, hence, is simpler to
deploy than GSM.
◗CDMA cannot be deployed well in microcells.
◗CDMA systems have a higher risk.
◗CDMA systems have a higher cost.
◗Americans should adopt CDMA as Europe had mandated GSM but
were trying to sell GSM into the United States, representing unfair
competitive practice.
◗GSM is deployed worldwide, resulting in roaming capabilities, and
the worldwide acceptance makes it the dominant standard.
◗CDMA systems are difficult to design due to the “cell-breathing”
problem.
Greater range The claim for greater range for CDMA was made
because the gain achieved by the despreading process allows the receiver
to operate at a lower signal level and hence at a greater distance from the
transmitter. While this is true, in heavily loaded systems, the interference
from other mobiles and from neighboring cells is such that the range is
reduced and CDMA only achieves a similar range to TDMA.
Lack of frequency planning Because the same frequency is used in
each cell within CDMA, there is no need to make a decision as to which
frequency to allocate to which cell, unlike TDMA. However, there are
now many automated planning tools that can rapidly perform the TDMA
frequency allocation process; hence, this is no longer a serious handicap.
Areas of conflict 325
Macrocell/microcell If a microcell is deployed under a macrocell in a
CDMA system, then it must use a different frequency. Otherwise, the
transmissions made by the mobiles in the macrocell will be at a much
greater power level and will cause excessive interference to the microcell.
However, if the number of channels required in the microcell is small,
then the assignment of an entire frequency may be wasteful. As a result,
using a hierarchical cell structure may reduce the efficiency of CDMA.
Risk Until recently there was a relatively high risk associated with
deploying a CDMA system because no other system had been deployed
and the problems that might arise were not well known. However, there
are now more than 100 CDMA networks around the world and the risk
has rapidly fallen to a level similar to that of a TDMA system.
Cost As with the other conflicts described in this chapter, cost is diffi-
cult to compare until there are quotations from manufacturers for identi-
cal networks. What appears to be the case is that CDMA base stations are
more expensive than TDMA base stations but have a higher capacity and
so fewer are required. This generally causes CDMA to be less expensive in
a high-capacity situation, but relative cost must be determined for a spe-
cific case.
Open markets There is much discussion in mobile radio as to what
extent markets are open around the world, allowing equal competition
for all standards. This is a complex political issue rather than one that can
be resolved by analysis, but nevertheless, one of which the engineer
should be aware.
Roaming For some users, the roaming that GSM offers will be an
advantage. However, in a typical network only around 5% of the users
roam, so this is not a key issue. The issue of the dominant standard is only
important if the lower economies of scale push up CDMA prices too high,
or worse, result in the system eventually being withdrawn from the mar-
ket. However, given the number of manufacturers involved in CDMA
products, the latter seems unlikely.
Breathing problems Deployment of CDMA systems has shown that
there can be problems with cells “breathing.” As a CDMA cell becomes
more heavily loaded, the interference increases. This results in a reduc-
tion in the link budget (because the effective noise floor is now higher)
and a corresponding reduction in range. As a result, the size of cells can
326 The Complete Wireless Communications Professional
fluctuate with load. This tends to make cell planning problematic and
often results in the system having to be designed so that there is substan-
tial overlap between cells. This ensures that even when cells are con-
tracted, there is still good coverage available.
14.4.4 Analyzing the debate
There appear to be several key issues.
◗Resolving the capacity difference between the two systems is not
possible until deployments have taken place. However, it would
seem likely that the capacity of CDMA systems is greater than that
of GSM.
◗It is only possible to determine the relative costs of the two systems
for a particular deployment at a particular point in time, but it seems
likely that generally CDMA will be more expensive than GSM due
to the increased complexity of the system.
◗There are emotive arguments that cloud the issue.
◗The large amounts of money and reputations at stake mean that
any rational discussion is unlikely.
The complete wireless professional would have realized early on that
general arguments about capacity and costs were pointless but that in
situations where capacity was essential, CDMA was more likely to be
appropriate, whereas in situations where cost was essential, GSM was
more likely to be appropriate. The key step is to determine for a particular
network design what the different costs of the two systems would be and
to use this as a starting point for the analysis. The complete wireless pro-
fessional would have avoided arguments concerning capacity or general
arguments concerning costs as far as was possible.
14.5 Handling conflict
The examples presented here have, perhaps, provided a rather idealized
view of the manner in which conflict can be treated. For an engineer in a
manufacturer who is committed to a particular product, it may be difficult
to view the debate dispassionately; in any case, the employer expects the
Areas of conflict 327
engineer to support their product. As a consultant pressed for a view as to
which of two competing technologies is best, the answer “it depends”
does not seem to provide the certainty for which the client is looking.
However, there are a number of important lessons that can be learned
from this.
◗Where there are engineering issues, some can be solved using
analysis and skill, but there will remain insoluble issues that should
be recognized as such. A deep understanding of the underlying
mechanisms might help provide some guidance as to the likely
solutions to these problems.
◗In most cases, the key to the problem will be a financial appraisal
that may also include a cost-benefit analysis, but to be of any value
this will typically need to be for a specific situation.
◗The complete wireless professional will also need to cope with
financial issues, strategic issues, marketing and policy issues, and a
number of unknowns. These should be clearly identified and dis-
cussed with relevant experts.
The complete wireless professional will do a much better job of
resolving conflict than one with a more narrow focus. With the ability to
understand most or all of the relevant issues, he or she can put the engi-
neering problems into perspective. Such an engineer will be very valuable
in helping clients or employers find their way through the increasing
uncertainties in the world of mobile radio.
References
[1] Lee, W. C. Y., “Spectrum Efficiency in Cellular,” IEEE Trans. on Vehicular
Technology, Vol. 38, No. 2, May 1989, pp. 69–75.
[2] Akerberg, D., “Comparison of DECT and PHS,” Ericsson Report TY95:077,
Jan. 1996.
[3] Hamano, T., “PHS: The Technology and Its Prospects Outside Japan,” Mobile
Communications International, Nov. 1995, pp. 54–56.
328 The Complete Wireless Communications Professional
Management
Alice asked, “Cheshire-Puss, would you tell
me, please, which way I ought to go from
here?” “That depends a good deal on where
you want to get to,” said the cat.
Lewis Carroll
15.1 Introduction
The complete wireless professional needs to
have good managerial skills. He or she will
need to be able to manage and motivate staff
and be knowledgeable about human resource
management and many other similar disci-
plines. He or she will play a role in developing
corporate strategy, particularly in the areas
where technology is a key input. This section
concentrates on the development of strategy
since it is arguably one of the most impor-
tant skills and the one that lends itself best
to textbook analysis as opposed to human
resource skills that are better taught in
workshop settings. As discussed in more
329
Contents
15.1 Introduction
15.2 An overview of
management
15.3 Understanding
corporate strategy
15
CHAPTER
detail in Chapter 16, the complete wireless professional would often
benefit from earning MBA in order to have a better understanding of the
workings of management. A good overview of all management topics can
be found in [1].
15.2 An overview of
management
A complete manager would need to have an understanding of the follow-
ing areas.
◗Management theory covers areas such as the design of the organiza-
tion and some of the classic management theories relating to the
division of labor and the extent to which managers should be con-
cerned about their staff. The complete wireless professional will
typically not need to become overly involved in this area.
◗International management covers issues associated with international
trade, including an understanding of the different cultures; why
companies become global; and the different politics, economic, and
technical factors in other countries. Although not essential, the
complete wireless professional might find it helpful to have some
appreciation of the international dimension.
◗Unless setting up their own company, entrepreneurship is not an area
of which the complete wireless professional needs to be particularly
aware; however, many organizations now value individuals who
can show entrepreneurialism while within the company and this
may be something the complete professional may wish to develop.
◗Planning and strategic management covers the way in which decisions
affecting future areas and products for the company are made and is
important for the complete wireless professional to understand.
◗Strategy implementation covers the practical means of putting a new
strategy into action, making sure it is accepted by all the staff and
that everyone is working toward the new goals. When in a manage-
ment role, this will be one of the tasks of the complete wireless
professional.
330 The Complete Wireless Communications Professional
◗Decision making looks at the more scientific ways to make a decision
between one project and another or between different ways of
investing money. Most engineers are intuitively good at this any-
way because it typically involves logic and the application of prob-
abilities to outcomes.
◗Organizational structure and behavior covers the division of the work,
the departmentalization and span of management, functional and
matrix organizations, and ways to go about designing an organiza-
tion. It is not something in which the typical complete wireless pro-
fessional will be heavily involved, but a passing understanding of
this area may be useful.
◗Authority, delegation, and decentralization covers the nature of author-
ity, the delegation of power to line staff, the design of jobs, and
means of enpowerment. As before, an understanding of this area
may be useful to the complete wireless professional.
◗Human resource management covers areas such as recruitment, selec-
tion, orientation and training, appraisal, promotion, and discipli-
nary action. It is something in which the complete wireless
professional may get involved if they build a team around him or
her but hopefully something in which he or she will have support.
◗The management of change is a complex issue involving a need to
get employees to accept new ideas and change the manner in which
they are working. This is not typically something with which the
complete wireless professional would need to be involved but about
which he or she should understand the principles.
◗Leadership covers the attributes of the people with power in the
organization and looks at a range of different leadership styles.
Exceptional leadership skills will not be an essential characteristic of
the complete wireless professional, but some leadership skills will
be helpful in his or her role.
◗Finance and accounting looks in more detail at the areas introduced in
Chapter 8.
◗Information systems covers the design and use of management infor-
mation systems and will cause few problems for engineers accus-
tomed to computer technology and statistical analysis.
Management 331
The remaining part of this chapter focuses on the important topic of
strategy.
15.3 Understanding corporate
strategy
The need for strategy is epitomized by the quote at the top of this chap-
ter—without a firm plan as to where an organization is going, it is likely
not to get anywhere. Many organizations seem to try to go somewhere
without understanding where, and the result is general confusion and
rarely success in the marketplace. The development of strategy is a rela-
tively new concept—most organizations in the sixties and seventies had
little idea of where they were going unless they happened to have entre-
preneurial leadership. It was not until the 1980s that the science and
practice of corporate strategy was developed, mostly by one man, Michael
Porter, widely recognized as the giant in this area. All textbooks on corpo-
rate strategy, such as [2, 3], reference Porter widely. Actually, Porter’s
own books are quite hard work, and it is better to read others’ interpreta-
tion of his words.
Corporate strategy is all about beating your opponents by devising
and implementing a strategy that will allow you to sell more products or
services than the competition. To some extent this arena could be com-
pared to a game of chess. In the 1960s and 70s, this game was being played
with little understanding of good strategy and with ill-defined rules. In
the 1980s, some companies started to understand what Porter was saying
and became much better players. They won the next games of chess easily
and went on to the become the great organizations of the 1980s, those
featured in [4]. By the 1990s, most surviving organizations had assimi-
lated much of the knowledge on strategy and the game of chess was again
between equal opponents but played on a higher level. Any organization
that does not understand strategy will come to the chess board ill-
prepared and will be soundly beaten by better opponents. The best way to
understand strategy is to read one of the excellent books referred to previ-
ously. All the remainder of this section does is to provide a summary of
some of the key issues.
Strategy starts with an analysis of the situation facing the company,
including all internal and external factors. From this understanding
332 The Complete Wireless Communications Professional
comes a selection of possible strategies that can then be analyzed to deter-
mine which is the most appropriate. Key is the correct understanding of
the current situation—from this, potential strategies seem to flow readily.
The following are tools to help understand the situation. They are typi-
cally used in a brainstorming session where a team of people take each
heading in turn and list every factor they can think of, however appar-
ently stupid, in order to try and capture all the issues.
PEST and SWOT These are acronyms that help the strategist remem-
ber to analyze a range of different areas. PEST stands for political, eco-
nomic, social, and technical.
◗Political: An understanding of political changes (such as a change of
government) or trends (such as deregulation) that are likely to have
an impact on the sector in coming years; for manufacturers this
needs to be understood for a number of different countries.
◗Economic: An assessment of the economics of the country (such as
GDP projections) and the economics of the users (such as whether
operators will be able to borrow money) allowing the ability to pay
for a product to be assessed; for example, a projection of high GDP
growth would suggest richer citizens who may be prepared to spend
more on mobile communications.
◗Social: Relevant social factors, such as a backlash against the use of
mobile phones in public places, or an increase in crime requiring
mobile phones for security.
◗Technical: A look at technical developments that might change the
market; this includes major breakthroughs such as new batteries,
general trends such as small and cheaper handsets, and develop-
ments in related industries such as the capability to send very high
data rates down fixed lines.
SWOT stands for strengths, weaknesses, opportunities, and threats.
◗Strengths: The things that the company does well or has as attributes,
such as a well-known name, excellent distribution channels, or
good financing capabilities.
◗Weaknesses: The opposite factors such as a lack of skilled staff or an
outdated manufacturing plant.
Management 333
◗Opportunities: Areas the company might enter or new products they
might develop, such as adding a WLL portfolio based on existing
cellular products.
◗Threats: Things that competitors might do that would damage the
company such as introducing a much cheaper product or one that is
technically superior in a manner that will bring benefits to the
users.
Five-forces model This model was developed by Porter to help people
assess the state of their industry. Porter’s model is shown in Figure 15.1.
Like the acronyms, the intention is that the strategist considers each
of the following different areas.
◗Threat of new entrants looks at whether new companies might enter
the market. To understand this it is necessary to consider the barri-
ers to entry; for example, a new cellular equipment manufacturer
requires expensive manufacturing plant and new operators require
spectrum, which can be difficult to get.
334 The Complete Wireless Communications Professional
Competition
within the
industry
Bargaining
power of
suppliers
Threat of new
entrants
Bargaining
power of
buyers
Possibility of
new products
Figure 15.1 The five forces model.
◗Bargaining power of suppliers considers whether the suppliers will
alter the way in which the company works by increasing prices,
insisting on certain strategies, or favoring a competitor.
◗Bargaining power of buyers is similar for the buyers. Buyers may be
able to negotiate reduced prices or changes to equipment. This is
especially true in the manufacturing industry where cellular opera-
tors are able to negotiate excellent discounts for large orders.
◗Competition within the industry looks at what the existing competitors
might do based on knowledge of their current strategy and looks at
“what-if” scenarios in the same manner that a chess player will
examine all viable moves his or her opponents might make.
◗Possibility of new products tries to look very widely at what might
come along in the future. Classic examples are glass bottle makers
who failed to see the advent of plastic packaging. To look at what
might happen requires a very broad mind, but suggesting a number
of possibilities such as wristwatch communicators1and then look-
ing at their likelihood and implications is an important exercise.
The value chain This is another concept developed by Porter, show-
ing that each part of the company contributes to the “value” added to the
end product. In making the company as efficient as possible it is important
to assess each part of the value chain and ask whether the operation could
be outsourced and how the efficiency of the operation could be graded. A
possible value chain for a cellular operator is shown in Figure 15.2.
The value chain also shows the interrelationships between different
parts of the company. This may allow areas of shared expertise to be iden-
tified and, if the company has other divisions, allow sharing of some areas
of expertise between the different divisions.
Having used these tools, the situation facing the company should be
clear. Strategy development then follows through more brainstorming,
development of spreadsheet models, research on particular points raised,
and good ideas from those present. Devising a strategy, like inventing a
new product, is not something that can be done by following rules but
Management 335
1. Many mobile phone manufacturers are striving to devise the wristwatch communicator
and a number of prototypes have already been exhibited. To build such a device requires
a shift in thinking away from high-power transmitters, keypads, and speakers integrated
into the phone. The development of such devices may change the power base within the
world of mobile radio.
requires creativity coupled to a good understanding of the situation. In
devising strategy the following points are relevant.
Price or quality Porter, looking at different companies, said that basi-
cally a company can compete on price and become the lowest cost pro-
ducer; or can compete on quality, producing a product for which
customers are prepared to pay more because of some differentiating fea-
ture; or can focus on a narrow segment of the market that is so small that
other companies will not be inclined to enter the market. He said that
companies should follow one of these three strategies—to try and do
more than one, or to follow none actively, was to get “stuck in the mid-
dle,” leading to a lack of direction and eventual failure. Companies that
decide to compete on price must have the lowest cost production of all
their competitors, otherwise they will enter into a price war that they will
lose. Such companies focus on being “lean and mean” with minimal over-
head and new techniques for cutting costs—direct line insurance compa-
nies who removed the cost of shops in town centers are a good example of
this. Companies that compete on quality should have some attribute that
it is difficult for others to copy, such as the capability to produce the small-
est phones on the market, and need to work continually to maintain this
advantage since others will seek to copy. However, while they have a
clear differentiator, this can be used to maintain high prices and high
profitability—Ferrari is a good example where the name, image, and
engines developed in Formula One racing provide a combination of fea-
tures that others cannot easily copy. Finally, companies that look for a
336 The Complete Wireless Communications Professional
Equipment
procurement Cellular
operations Marketing Sales
Network deployment and maintenance
Human resource management
Development of new services and technologies
Figure 15.2 A possible value chain for a cellular operator.
small niche should make sure that they have a product that it is not
worthwhile for a large company to copy.
When devising strategy it is important first to decide whether the
company will compete on price or quality. This fundamental decision
then has implications for the detailed strategy adopted to achieve the tar-
get point on the grid. A much more detailed discussion of this technique
can be found in [2].
Necessary outputs—the mission statement and the statement of
strategy Once the strategy is decided upon, it is important to
implement it. Implementation and change management is a large sub-
ject, probably outside the scope of the complete wireless profession-
al’s expertise. However, the complete wireless professional will want
to help in the first stages of communicating the new strategy. These
are conventionally the much derided mission statement and strategy
documents.
◗The mission statement should be a short, concise statement of exactly
what the company is trying to achieve. It should make it clear what
are the most important factors. For example, one manufacturer
might, as a mission, say, “We will produce the lowest cost cellular
handsets on the market,” whereas another might say, “We will pro-
duce the smallest and most innovative handsets on the market,”
while another might say, “We will produce the widest range of
handsets to fit all the uses and all the markets.” The last statement
would be a poor strategy because of the attempt to do everything
rather than concentrating on price or differentiation. Drafting the
mission statement often takes some time, but at the end everyone
should be clear on the single most important goal.
◗The strategy should indicate how the goal stated in the mission state-
ment will be achieved. For example, if the mission is to produce the
lowest cost handsets, then the strategy might be to work with
suppliers to cut costs and to move production to the lowest cost
countries. The strategy should be a list of clear steps that will be fol-
lowed to achieve the required objective. Anyone reading the strat-
egy should be in no doubt that if implemented successfully the
strategy would result in the mission being realized.
Management 337
There is much more than this to strategy. For example, one of the
strategies might be to attack a competitor. The attack may be on the com-
petitor’s strengths to discredit them, on their weaknesses to quickly gain
market share from them, on many fronts simultaneously, on segments
where the competitor has little presence, or in “hit and run” attacks
where special offers for a limited period take market share before the
operator has time to react.
Developing strategy is a big risk business. An inappropriate strategy
could ruin the company. The complete wireless professional would be
advised to cut his or her teeth on the numerous case studies that are avail-
able from management schools. Even better is to complete an MBA
where he or she would be guided through the development of strategy in
more detail.
References
[1] Stoner, J., and R. Freeman, Management, London: Prentice-Hall, 1992.
[2] Thompson, A., and A. Strickland, Strategy Formulation and Implementation,
New York: Irwin, 1992.
[3] Johnson, G., and K. Scholes, Exploring Corporate Strategy, New Jersey:
Prentice-Hall, 1993.
[4] Peters, T., and R. Waterman, In Search of Excellence, New York: Harper and
Row, 1982.
338 The Complete Wireless Communications Professional
The complete
wireless professional
Personally I’m always ready to learn,
although I do not always like being taught.
Winston Churchill
16.1 Introduction
The first fifteen chapters of this book, in gen-
eral, provide an overview of the areas of
knowledge required to fully understand the
world of mobile radio and partake in
the conflicts that will undoubtedly occur
in the future. This chapter turns to the indi-
viduals themselves and to the tools they can
use to advance their standing, to enhance
their capability to intervene in debates, and to
promulgate their opinion more widely than
would otherwise be possible. This chapter
looks at the topics of conferences, publica-
tions, research, and qualifications for the
complete wireless professional.
339
Contents
16.1 Introduction
16.2 Conferences and
publications
16.3 Links with
research organizations
16.4 Qualifications
16
CHAPTER
16.2 Conferences and
publications
Conferences and publications are useful vehicles for the complete wire-
less professional to use to publicize his or her analysis of particular situa-
tions and to get a wider view of the issues and problems involved in a
particular situation. By appearing at conferences, the complete wireless
professional will also enhance his or her own standing, which will be use-
ful for a number of reasons:
◗Making others more receptive to listen to his or her viewpoint
because of the kudos that speaking at conferences can provide;
◗Making it easier to approach key decision makers;
◗Increasing the wireless professional’s visibility, which will help his
or her future career prospects.
Getting invited to speak at the conference Getting invited to speak
is relatively simple. Most conference organizers spend a lot of time
searching for appropriate speakers. Simply by contacting them with a list
of topics on which you would be happy to talk will normally result in
a flood of invitations to speak at forthcoming conferences. Getting to
know the conference organizer and meeting with him or her occasionally
can even result in taking part in some of the preliminary planning
of the conference, providing an opportunity to shape the conference
along the lines that are personally most relevant. Conference organizers’
contact details can be readily obtained from the back of conference
advertising material.
Preparing the presentation Preparation is a task that becomes
much simpler with experience. Sufficient time needs to be set aside for
preparation—those talks that have been prepared on the train on the way
to the conference are generally easy for the audience to identify because
they lack structure and thought. However, presentations can also be
overprepared. In particular, writing out the complete talk is widely
acknowledged to result in poor presentations due to the tendency to then
read the presentation rather than speak to the audience, resulting in
wooden and insincere presentations. The best form of preparation is to:
340 The Complete Wireless Communications Professional
1. Make a list of the key points to be delivered during the
presentation.
2. Check on the length of time allocated for the presentation and
take off 5 minutes for questions and overruns from previous
speakers.
3. Produce a first draft of the slides for the presentation, assuming
that each slide should take around 2 minutes to present (over
time individuals will get to know how long they tend to talk per
slide). Make sure that the size of the text is sufficient to be read
from the back of a large hall and the background does not reduce
its legibility.
4. Go to a closed room and talk aloud through the presentation, tim-
ing how long it takes. During this rehearsal make notes on the
slides where topics did not seem to flow or where more prompts
might be required to remember the key points.
5. Reduce the length of the presentation until it is 10 minutes less
than the length of time assigned (so that even allowing the
5 minutes for questions the presentation will still be 5 minutes
short). This is a very useful tactic that helps prevent the standard
problem of talking too fast during the presentation. Knowing that
the presentation is too short tends to result in speakers talking
more slowly to avoid finishing too early. A presentation that is too
long is generally disastrous for the audience.
6. Redraft the presentation based on the rehearsal so that the flow of
the presentation is clear and the audience will easily understand
the starting position, the assumptions made, the logical deduc-
tions, and the conclusions. Presentations that flow clearly from
slide to slide are generally well received.
7. For those who are more experienced at presentations, at this stage
consider whether there is any way that the start of your presenta-
tion can be made a little different, such as by using a striking
graphic or a key statement on the first slide rather than the
expected “Contents” slide. This helps grab the attention of the
audience. For example, a first slide stating “The market for TETRA
The complete wireless professional 341
is only one-fourth that of current assumptions” will generally
work better than a contents page with the bullets: Introduction,
TETRA, The Market, Conclusions.
8. Re-rehearse the presentation, timing it again to ensure that it is
still too short. (Even if the presentation really is too short, most
audiences prefer this to overly long presentations that impinge on
their lunch breaks.) Again check that there is a clear structure and
flow to the presentation.
9. If necessary, continue to revise and rehearse the presentation.
With more experience, it becomes possible to shorten this procedure
to typically a single rehearsal and often only one draft of the slides. It is
important to remain very critical of one’s own presentations. Colleagues
will typically always say that the presentation was “great” because that is
human nature. After every presentation it is worth asking:
◗Did the presentation flow well while it was being given, or did it
have the feeling that it was jumping from topic to topic?
◗Was it presented to time?
◗Did the audience appear restless?
In preparing the slides it is important not to overcrowd them with
detail (many presenters end up apologizing for “busy slides”). A tendency
is to add graphics to every slide on the basis that these will somehow grab
the attention of the audience. In practice, simple slides, with graphics
only where they really add value, are much more appropriate since they
result in the audience focusing on the key points. It is quite routine for a
simple presentation, with no graphics, to be rated more highly by an audi-
ence than one comprising complex multimedia material.
Giving the presentation There is much skill in giving a good presen-
tation, but it is something that can be learned and should be carefully
studied by the complete wireless professional. The complete wireless pro-
fessional should aim to go on a two-day presentation skills workshop,
lead by an experienced presenter, where presentations are recorded on
video and replayed for analysis. Not only will this help ensure that the
skills are learned but will also do much to reduce nervousness. Unfortu-
nately, most engineers are introspective individuals not given to
342 The Complete Wireless Communications Professional
flamboyant presentations and often require training to give a more open
presentation. Some of the key points to try to remember when giving the
presentation are:
◗At most engineering conferences most of the other presenters are
terrible, so it does not take much to appear to be a good presenter.
◗Most presenters overrun their slot despite thinking they could
never talk for that long.
◗Talking too fast is a standard problem and one that dramatically
reduces the message being delivered.
◗Looking at the audience is essential—it is best to have some system
where it is possible to see the slides while still looking toward the
audience (e.g., using a PC to run the projection or by interleaving a
paper copy of the slides with the acetates and putting the paper copy
on the lectern as the acetates are placed on the projector).
◗Pausing occasionally and altering the tone and volume of voice
will help keep the audience awake, especially in the difficult after
lunch slot.
◗Never read a presentation from a script and try to avoid standing
behind a lectern if possible since the latter can tend to place a “bar-
rier” between the speaker and the audience.
When in the audience it is worthwhile to try to analyze what the
interesting speakers are doing that allows them to keep your attention.
Often it will be the combination of humor, a detailed grasp of their sub-
ject, and an incisive analysis of the situation. The latter two are things that
every wireless professional should strive toward in his or her presenta-
tions. Humor is more difficult—forced humor is often worse than no
humor at all and the general advice is only to be humorous if it comes
naturally to you.
Becoming the chairman Chairing a conference is often considered a
highly prestigious accolade given to those who are recognized as industry
gurus. Actually, this is far from the truth. The conference organizers typi-
cally do not know who the gurus really are and, in any case, are easily
bribed by the conference sponsors to give their key staff the chairman’s
role. The complete wireless professional should seek to become a
The complete wireless professional 343
chairman because of the prestige associated with it but should realize that
getting to be a chairman is something to be worked at in discussion with
the organizers rather than something that will naturally follow from
years of good work. A very good, if rather obvious, tactic is simply to say
to the organizer that you would like to be the chairman. Deliver a CV
showing how you have achieved much and keep trying. Do not be put off
by a few failures—in many cases, this will be because someone has paid
money to be the chairman.
To many at a conference, the chairman might seem to have an easy
time, just introducing the speakers and asking some questions. Chairmen
can have an easy time, but doing the job well is exhausting. A good chair-
man should:
◗Provide interesting and stimulating opening remarks.
◗Read and rewrite the speaker biographies so they are short and to
the point.
◗Have a number of perceptive and penetrating questions for each
speaker.
◗Be ruthless in keeping the conference running on time—most
speakers overrun even the longest slot and being late for lunch is
what the delegates hate the most.
◗Run discussion sessions, seeding the discussion with controversial
(but well-founded) remarks to get audience participation and mak-
ing sure that the discussion does not become a dialogue between a
speaker and someone in the audience by suggesting this discussion
takes place in the coffee break.
◗Help the conference organizer by reading messages and relaying
logistics.
◗Provide a summary of the conference that extracts the key points
rather than just summarizes what everyone says and analyses these
points to provide some cogent conclusions.
Most of these tasks have to be performed during the day, while listen-
ing to presentations, keeping an eye on the time, and thinking up ques-
tions. The role of a chairman is worthwhile but not to be undertaken
lightly!
344 The Complete Wireless Communications Professional
Writing papers Written papers are also a good vehicle for promoting
views (and for self-promotion). There is a wide range of different types of
written papers.
◗Learned journal articles normally based on research work and dis-
cussing some new idea or topic;
◗Institute magazine articles that are less mathematical and more
tutorial but nevertheless are still “learned”;
◗Papers for monthly magazines that tend to be much more relaxed in
style will rarely have any mathematics and will often not discuss
any new ideas;
◗Conference papers that should support the presentation given.
The learned journal articles are normally the preserve of the research
worker who has been investigating some new topic. These journals are
typically only read by academia and research establishments, which will
not be where either the complete wireless professional, or the people he
or she is seeking to influence, will reside. Although it might be helpful for
the complete wireless professional to have written some of these learned
journal articles in the past in order to boost his or her credentials, this is
typically not where he or she should be focusing his or her attention.
The institute magazine articles (e.g., the IEEE Communications Maga-
zine or the IEE Electronics and Communications Journal) are somewhat more
relevant. They will be read more widely by other engineers and allow the
chance to analyze existing situations. They also tend to be more respected
than articles in monthly magazines. However, they will only be read by
other engineers and, in the case of the analysis of a conflict situation, a
wider readership including managers and others in the industry might be
more appropriate.
Monthly magazine papers carry the lowest level of kudos but typically
the highest circulation and are a very good vehicle for the complete wire-
less professional to express his or her views on a current situation. Before
writing the article, look carefully at some back issues of the target maga-
zine to gain an understanding of the style and length of published articles.
Reference the editorial contact information inside the front inside cover
and contact them to discuss the possible contribution.
Just like presentations, the key to a good paper is clarity and accuracy.
A paper that has a clear starting point and a clear direction and works
The complete wireless professional 345
through in an easy-to-follow manner to some logical conclusions will be
much better than most of the other papers published and widely read.
Papers that just seek to act as an advertising vehicle should be avoided
since these are rapidly glanced through by readers.
One of the important attributes for a complete wireless professional is
a good writing style. Sadly, it is very rare to find an engineer who can
write well—most are more interested in numerate rather than literate
disciplines. The best way to learn to write well is to work for someone who
can write well and is prepared to spend the time criticizing written work.
If this is not possible, courses on writing technical reports will help, as will
reading well-written novels. The key to a good writing style is clarity of
thought and language and brevity of words. Carefully reread articles
before they are sent to the journal asking:
◗Are the key ideas clearly brought out?
◗Could anyone follow the logical steps described here?
◗Is the text “tight” and unambiguous?
When reading early drafts of papers, views are often expressed that
the paper needs “polishing.” This is generally unhelpful to the author,
since if he or she knew how to polish the paper, he or she would probably
have done it already. The underlying meaning is that the paper contains
all the material that is required but does not read well. This may be
because ideas do not flow clearly and the sentence and paragraph con-
struction is such that sentences often need to be read more than once to
understand them. When reading your own paper, try to look for areas
where the wording and the structure could be improved in order to make
it simpler to understand.
16.3 Links with research
organizations
Use of research Keeping in touch with research is essential for the
complete wireless professional. The research topics of today often become
the practical technologies in use tomorrow. The complete wireless profes-
sional will need to be aware of research in order to design new products or
346 The Complete Wireless Communications Professional
services, to be able to resolve conflict, and to understand and predict
future trends. The simplest way to keep in touch with research topics is to
subscribe to the relevant professional journals (e.g., the IEEE in the
United States) and to periodically attend conferences. The only problem
can be the difficulty in struggling through academic papers—journals that
periodically publish reviews and tutorials can be very helpful in providing
a solution; for example, see [1–5]. Engineers in large companies may
have access to their own research laboratories, which they can use to
investigate particular topics. Intranets may also provide a useful summary
of work being performed within the company. Beyond this, the engineer
can become more proactive with sponsorship or participation in multi-
party research programs.
Sponsorship of university research If the company does not have
its own research department or if the research department does not have
the capacity to perform all the work required, then it can be “subcon-
tracted” to universities. Universities often provide an inexpensive means
of getting work performed. However, they may do so by harnessing indi-
viduals with their own agenda, which is often to obtain a doctorate. These
individuals will only wish to work on “major” problems that will provide
sufficient material for a thesis and may take many years to complete.
Hence, universities are often very cost effective for long-term research
topics (such as adaptive antennas) but, depending on the university and
the individuals involved, may be less suitable as the work becomes closer
to commercial reality. Further, the relative lack of control over the
research may make universities less well suited for work of the highest
importance to the company, although again, this will vary from univer-
sity to university.
Another way to use universities is simply as a means for generating
new ideas. Often university staff and graduates are highly inventive peo-
ple who can think in unconstrained ways. As a result they will often gen-
erate a myriad of new ideas, a few of which may become useful to the
company. The role of the complete wireless professional then becomes
one of filtering out the good ideas from all the various ideas suggested.
This is a surprisingly difficult role. It is human nature to be skeptical of
new ideas, especially those furthest removed from current practice;
hence, it is easy to dismiss too many of the new ideas. The com-
plete wireless professional should remember this in-built tendency and
should think carefully about each of the ideas, discussing them with
The complete wireless professional 347
colleagues where appropriate. Some companies commission universities
to give them research briefs and open days to keep abreast of what
the university is doing, often favoring those universities where the
professor of communications has a good track record of generating suc-
cessful new ideas.
National and international research programs There has been an
increasing trend toward the use of multiparty research programs, espe-
cially in Europe where the Research into Advanced Communication in Europe
(RACE) and the Advanced Communications Technologies (ACTS) programs,
sponsored by the European Commission, have generated many thou-
sands of man-years of research. A program like ACTS invites a consor-
tium to put together a research program and bid for ACTS funding.
Typically, the EC will fund around 50% of the project with the remainder
coming from the participants. The aim is both to maintain Europe’s
leadership within mobile radio engineering and to foster cooperation
between European companies. The history of such programs has been
mixed with some generating excellent results, but in other cases the work
falls below the highest standards and can disappoint. The difficulty is that
the organizations within the consortium often have different goals and
different remits. The academics typically want to publish, whereas the
industrial partners want exploitable results that they can patent. In some
cases, differences such as these, coupled with some partners who did not
take the research seriously, has resulted in the premature closure of proj-
ects by the EC monitoring committee.
An interesting case of how some of these programs did not meet their
goals was the TDMA versus CDMA arena (see Section 14. 4). The EC com-
missioned two projects, one for each access scheme, to determine the best
possible performance of the schemes. The idea was that by comparing the
results of the two projects, Europe would be able to make a rational deci-
sion as to the selection of the air interface for third generation mobile
radio (see Chapter 11 for a description of what finally happened). How-
ever, both the projects were delayed and, when finally completed, their
results incompatible. Not all research projects fail to live up to promise
and some have provided very impressive results, but it is clear that careful
selection of partners and project management is required to achieve
success.
348 The Complete Wireless Communications Professional
16.4 Qualifications
It is likely that the complete wireless professional will have a degree in
engineering, probably electronic engineering or similar from a good uni-
versity. This is a prerequisite both to provide sufficient background
knowledge to be able to understand the fundamentals of mobile radio
systems and to demonstrate sufficient intelligence and application to
overcome the challenges that will be faced in the future. For most engi-
neers, the degree may be the only form of qualification. However, there is
much to be gained in further qualification.
A Ph.D. is a useful, but not essential, tool. It engenders more respect
than would otherwise be the case, which can be useful when making a
point of view. Assuming that the Ph.D. was conducted on a relevant topic,
it can dramatically improve the understanding of how mobile radio sys-
tems work. The best Ph.D. would be one that requires the development of
a complete simulation of a mobile radio system. Writing such a simulation
is an excellent education in all the detailed aspects of mobile radio system
design. During the Ph.D., immersion in the university environment can
be helpful. Understanding the way in which research is performed is use-
ful when dealing with research institutions. Universities can be usefully
harnessed by industry to perform certain research work at a relatively low
cost, and an understanding of the individuals in the university and their
aims and aspirations helps in this area. The complete wireless professional
is likely to have to read learned papers from time to time in order to assess
new ideas, and time spent at universities will make this easier. However,
the complete wireless professional will not want to spend too much time
in a research environment where his or her much broader skill base
would be wasted.
An MBA is also useful. Again this engenders respect and prevents the
engineer from being pigeonholed as a “techie.” Although the complete
wireless professional may not have a large team of people to manage, he
or she will be involved in financial and strategic issues; an understanding
of these will be very helpful in his or her subsequent career.
The complete wireless professional should not scorn the national
electrical engineering institutions (e.g., the IEEE in the United States).
Institute membership brings with it increased respect, chartered engi-
neering status, and a useful source of information on new developments
The complete wireless professional 349
in mobile communications. Not only should the complete wireless pro-
fessional join these institutions, he or she should try to increase his or her
rank in the institution as often as possible, passing through senior mem-
ber to eventually fellow status. Partaking in committees and advisory
panels further enhances prestige and provides useful contacts to those in
the business of generating new ideas.
The complete wireless professional should be well aware of his or her
worth to companies. Engineers who are able to understand the wider
financial and strategic issues, are articulate and able to write well, and can
resolve conflict are very rare. The complete wireless professional will be in
very high demand and able to command a salary level much higher than
other engineers. The complete wireless professional should set his or her
sights high—he or she will be able to achieve much in his or her career.
References
[1] The IEE Electronics and Communications Magazine, published bimonthly by the
IEE, London.
[2] The IEEE Communications Magazine, published bi-monthly by the IEEE, New
York.
[3] The IEEE Spectrum Magazine, published bimonthly by the IEEE, New York.
[4] The IEEE Journal on Selected Areas in Communications, published bimonthly by
the IEEE, New York.
[5] The Bell System Technical Journal, published quarterly by Bell Laboratories,
New Jersey.
350 The Complete Wireless Communications Professional
Appendix A
Erlang B macro
This macro will work on a Excel spreadsheet. When called with the
traffic level in Erlangs and the grade of service as a blocking probabil-
ity (e.g., 1%), it will return the number of circuits required.
‘ Function to return the Circuits required for a given traffic
‘ figure and Grade Of Service
Function Erlangb(traffic As Single, gos As Single)
Dim top As Single
Dim bottom As Single
Dim circuits As Single
top =1
bottom =1
circuits =1
While (top / bottom) gos
top =top * (traffic / circuits)
bottom =bottom +top
circuits =circuits +1
Wend
Erlangb =circuits −1
End Function
351
Appendix B
Mandating standards
B.1 Introduction
This appendix takes a look at whether spectrum managers or govern-
ments should mandate the use of particular standards when assigning
licenses to operate a particular service. This practice is widespread within
Europe (e.g., GSM/DCS1800 for cellular, TETRA for PMR/PAMR,
CT2/DECT for cordless) but is avoided in most other countries. There are
arguments both for and against the practice and these are listed in this
appendix.
It is important to note that this is a deep and complex issue around which there
is currently probably insufficient evidence to fully resolve the problem. This appen-
dix can only scratch the surface of the problem; much more detailed study is
required to fully expose all the issues.
An important issue that impinges on this debate is the degree of
“openness” of standards. Some standards are truly open, with internal
interfaces well defined and IPR issues controlled so that true multi-
sourcing is possible. Others contain proprietary interfaces requiring sig-
nificant royalty payments that may prevent effective competition. If
standards are not mandated and the market is open to competing
353
technologies, it is important to recognize that the widespread deployment
of standards that are not fully open could lead to distorted markets.
In Section B.2 each of the key issues is listed and discussed. In
Section B.3 some case studies are discussed, while Section B.4 presents
some implications.
B.2 The key issues
In this section the arguments used both for and against mandating a stan-
dard are examined. The real impact of some of these arguments will
become clearer after examining the case studies provided in Section B.3.
Arguments used for mandating a standard include the following.
Economies of scale It is claimed that mandated standards can result
in much greater sales than would have been the case otherwise, driving
down end user prices and hence maximizing the benefits.
Standards certainly provide the potential for economies of scale, the
question is whether mandating them improves this. GSM has achieved
excellent economies of scale, but arguably this is due to the openness of
the standard and its excellent design making it attractive around the
world. Other mandated standards have not achieved such good econo-
mies of scale. Key issues appear to include the ability of manufacturers to
spread research and development over many customers, a common spec-
trum allocation so that different mobiles are not required in each country,
and the ability to sell in most countries, that is, national markets are not
barred to standards. It would appear that producing well-designed and
truly open standards are the key factors in achieving economies of scale
and not the mandating of the standard.
Support to European industry It is claimed that mandated stan-
dards allow European industry to develop products that they are assured
of selling within the European market and provide substantial export
opportunities.
There are many problems with this argument, which can be summa-
rized by saying that mandating standards may be necessary for success but
is not sufficient—market conditions for the acceptance of the standard
must also exist. First, mandated standards do not necessarily ensure
354 The Complete Wireless Communications Professional
European sales—DSRR is a good counterexample to the obvious success
of GSM. Even where successful, mandated standards do not guarantee
success to the local industry—few of the CT-2 sales benefit the United
Kingdom, where the standard first appeared in Europe. Finally, manage-
ment research by Porter [1] and others has shown that a home market
biased toward national organizations tends to hinder rather than aid
international competitiveness; nor does using mandated standards to
encourage the growth of local industry seem to work despite it being tried
recently in Korea and other countries. Most management gurus would
argue that the likes of Nokia and Ericsson were world leaders due to their
innovation and skills and not due to a home market encouraged to buy
their products. Also, non-European companies (e.g., Motorola, AT&T,
NEC, and Panasonic) sell widely into the European market and only 5 out
of the current top 20 mobile operators are European. The case for this
argument looks weak.
European roaming It is argued that mandating standards across
Europe allows users to roam across Europe with a single terminal provid-
ing substantial end-user benefits.
GSM has clearly been successful in this regard and the benefits of
roaming are valued highly by a subset (around 5%) of its users. Around
8% of potential TETRA users claim to value roaming. Roaming provides
additional societal benefits such as enhancing the “borderless Europe”
concept through the equal provision of information and services to all
countries, enhances the mobility of businesses, and helps with the intro-
duction of the Information Society. At a lower level, roaming overcomes
the need for type approval in each country.
To some extent, if roaming is valued by users, then they would be pre-
pared to pay a premium for GSM-compliant systems and hence the mar-
ket process would provide a roaming facility. However, the societal
benefits are unlikely to be achieved by the market alone and mandating of
common standards may be necessary in this regard. Further study of the
importance of mandating standards to achieve societal benefits would be
worthwhile.
Interference It is claimed that a common standard and frequency allo-
cation reduces interference between neighboring countries and is
required for European frequency harmonization.
Appendix B 355
Cross-border interference is a major issue requiring significant effort
on the part of national operators. In principle, a spectrum mask is all that
is required to eliminate interference problems as is used in the United
States and elsewhere. In practice, detailed planning between different
operators across borders is essential. Interference may be particularly
problematic if very different multiple access mechanisms are in use on
either side of the border (e.g., CDMA and TDMA). However, the use of the
same standard does not seem to significantly ease this interference problem
and, hence, the need for mandated standards here appears weak.
Maintenance of Europe’s lead in mobile radio By continually
developing standards whose use is mandated, it is argued that Europe
continues to lead the world in mobile radio.
Arguably, it does not. The most innovative technologies are now aris-
ing within countries unconstrained by mandated standards. As men-
tioned earlier, many would argue the success of European countries
comes despite having imposed standards, not because of it. Finally, man-
dated standards do not prevent non-European countries entering the
market, so the success of a European standard may not necessarily bring
benefits to Europe.
Mandating a standard provides good spectrum efficiency
Since the spectrum manager can have an input into the spectrum effi-
ciency of the standard as it is developed, he or she can ensure that it makes
good use of the available resource.
This is not necessarily true. Good spectrum efficiency will only occur
if the mandated standard is the most technically efficient available. This
may not be so in many cases (e.g., it is argued that CDMA is technically
more efficient that GSM). Worse, spectrum pricing, as it is being consid-
ered by many countries, encourages efficient use of radio spectrum, but
mandating standards removes one degree of freedom for users to improve
their efficiency. (Note that changing technical efficiency is necessarily a
slow process as operators depreciate their existing equipment.)
Mandating a standard increases the openness of the standard
Having standards that are truly open is critical—this allows multiple
sourcing of components and terminals, resulting in a highly competitive
market. Mandating forces increased openness through a more intensive
356 The Complete Wireless Communications Professional
standards-making process and regulations regarding IPRs of mandated
standards.
There is little evidence to support this. Some mandated standards are
open (e.g., GSM) whereas others are highly proprietary (e.g., Linear
Modulation in the United Kingdom). It appears to be the rules and phi-
losophy imposed by the standards-making bodies such as ETSI that are
instrumental in achieving openness and not the act of mandating. What-
ever, it is clear that a standard that is not fully open in all respects should
not be mandated since this provides a monopoly advantage to the owners
of the key IPRs.
Achieving the single European market The EC has been keen to
encourage and mandate the harmonization of technical standards to
enable the free movement of goods and services across member states.
While open standards may promote free trade, idiosyncratic national
standards may act as nontariff barriers (e.g., the French choice of SECAM
for its color TV standard).
There is much truth in this. However, what is not clear is whether the
costs of opening the European market in this way exceed the costs of hav-
ing a closed European market in some areas. Possible costs might include
the potential adverse impact on innovation. This is an area that merits
further study.
Increasing consumer and producer certainty and encouraging the
early adoption of new standards Faced with a proliferation of
standards, producers and consumers are often unsure as to which tech-
nology to adopt in case they become stranded with an obsolete product or
locked into the single supplier of a proprietary standard. This may lead to
a waiting game in which players delay decisions until the market becomes
clearer. In extreme cases this prevents new technology emerging (e.g.,
the digital cassette). Government intervention in the form of mandating
the use of a particular standard can arguably overcome this problem.
There is certainly some truth in this. Further study would be useful to
determine whether this is a key issue or whether having only a single
standard (which was not mandated) but was manifestly open would be
sufficient. Also, increasing certainty will not help in the case that an inap-
propriate standard has been selected (e.g., DSRR).
Arguments used against mandating a standard include the following.
Appendix B 357
Enforced use of standard is contrary to a free market approach
and can distort the market This somewhat idealistic argument is
undoubtedly true. Enforced use of a standard occurs in few other areas
and inhibits innovation. If the “wrong” standard is selected (e.g., DSRR)
the users will suffer. If the “right” standard is selected (e.g., GSM) users
will gain little over a free market approach. If the standard is, perhaps,
more costly than available alternatives and the service competes with
another (e.g., PAMR versus cellular), then the market can be distorted
with resources wasted and competition restricted. If other market-
oriented approaches like spectrum pricing are in use, the consequences
may be significant.
This is undoubtedly true. Economists would argue strongly that the
restrictions on users should be limited to a minimum and that distorting
markets is a bad thing (the Communist regimes being the example of
extreme market distortion). Note, however, that the use of proprietary
technologies can distort the market to a greater degree than open stan-
dards and should be carefully avoided.
How can the government know best? To some extent this is the
same argument as the free market but asks how government bodies are
able to select the optimum standard. This is sometimes known as the
“blind giant problem.”
This argument is probably false. Government does not design the
standard, industry does. Government only mandates a standard devel-
oped by industry who have a better claim to understand the market. This
approach should continue.
Mandating standards prevents innovation There are some worry-
ing trends that might be attributable to mandating standards. Many of the
innovative ideas in mobile radio now appear to emanate from outside
Europe—these include CDMA cellular systems and frequency hopping
private radio systems. It is possible that these are early signs that mandat-
ing particular standards can stifle innovation. These new systems also
counter the view held by many that unless a standard is mandated, thus
almost guaranteeing a market, manufacturers will not take the risk of
investing in the development. Indeed, despite the closed market
in Europe, and hence reduced sales potential, manufacturers outside
Europe are still willing to take these risks where they see the potential for
volume sales.
358 The Complete Wireless Communications Professional
Mandating a standard is contrary to free-trade principles
In theory only European organizations (or non-European organizations
with a significant European presence) can partake in the ETSI standardi-
zation process (non-European organizations do not have voting rights)
and, hence, influence the development of radio system for sales into
Europe. The European market is then blocked, through a mandated stan-
dard, to U.S. equipment, for example. However, Europe expects to be able
to export its standards to the open U.S. market. Understandably, U.S.
companies can be annoyed by this behavior.
Loss of benefits arising from product differentiation and
increased consumer choice Much of this issue depends on the rela-
tive values that consumers place on standardization versus the benefits of
product differentiation and product choice.
The strength of this argument depends on whether the European
market could support more than one standard. If this is so, imposing a
standard may impose additional costs on the consumer relative to the free
market. Further investigation is required to determine in which situa-
tions more than one standard could be supported, but many would sus-
pect that in most cases only a single standard could be supported.
These arguments are now considered in the context of case studies in
the following section.
B.3 Case studies
In this section a number of case studies are considered that help to throw
light on the arguments presented in the previous section.
GSM This is the example that proponents of mandating standards
quote when they wish to demonstrate its success. With 198 networks in
92 countries and 100 million users at the time of writing, GSM is a stun-
ning success. Note, however, that even greater success has been achieved
by, for example, VHS and analog compact cassette without mandating a
standard—they have become de facto standards. Many countries are now
selecting GSM because of the competitive supplier market. However, the
real question is, “Would the standard have been less successful if its use
was not mandated”? While it is always difficult to conjecture as to what
might have been, it would appear that even if its use had not been
Appendix B 359
mandated in Europe it would have been widely adopted because, at the
time, it was the best system available. So we would argue that standardi-
zation was undoubtedly a good idea and mandating its use unnecessary
but not problematic since it would have been adopted anyway.
Proponents of mandated standards argue that mandating has led to a
European cellular industry so strong that it sells product into a frag-
mented U.S. market that has spent effort infighting rather than joining
forces to attack the world market. We would argue that the U.S. “prob-
lem” was a lack of a truly open U.S. standard and not a lack of a mandated
standard. Note also that the frequent recourse to litigation in the United
States can persuade spectrum managers to license a range of standards.
Mobile data In the United Kingdom particularly, but also throughout
Europe, mobile data networks have largely failed to live up to their initial
subscriber estimates. Some would argue that this was because there was
no mandated standard. (In fact, there was no standard at all, so it would
have been difficult to mandate one.) Others would argue that failure was
caused by too many competitors, poor marketing, a lack of focus on user
applications, and overly optimistic initial estimates. They would also
point out that there now is a de facto standard in Mobitex.
GSM is now starting to develop a significant data market, but this does
not necessarily prove that a mandated standard was required to penetrate
the market; rather that as an added extra on top of voice, data has more
appeal than when offered alone. The argument that a mandated standard
would have improved this market appears, with this cursory assessment,
to be weak.
Digital short-range radio This is often quoted as the counterexam-
ple to the success of mandating standards. The standard was developed
and spectrum allocated for its use, but since no equipment was developed
no one was able to offer a service. Now the spectrum has been reallocated
to other uses and proprietary technology allowed for this service. If there
had been no mandated standards, users could have had a service more
rapidly, potentially providing greater economic benefit to Europe. The
key problem was the development of the “wrong” standard. This is the
fundamental point: mandating a standard runs the risk of picking the
wrong one. Here, not mandating a standard would have certainly pro-
vided some benefits. (Interestingly, DSRR was developed in reaction to
concerns that a Japanese system would dominate the European market
and not in reaction to a perceived user need.)
360 The Complete Wireless Communications Professional
Digitally enhanced cordless telephone Here the mandated stan-
dard has resulted in limited and slow take up of the product. Other, argua-
bly more appropriate, technologies such as PHS have made much more
rapid inroads outside Europe. If a standard had not been mandated, then
possibly manufacturers may have produced a more appropriate technol-
ogy, easing introduction and increasing international competitiveness.
Again the “wrong” standard appears to have been developed with DECT
appearing to be attempting to simultaneously address the public and pri-
vate markets, preventing it from targeting a particular market well. The
CT-2 standard appeared to have a similar fate.
B.4 Implications
This appendix has briefly and superficially considered a wide range of
issues. This section tries to tie some of these together to arrive at some
conclusions.
Since approximately 1980, European spectrum managers have been
mandating the use of particular standards for particular spectrum bands.
This practice appears to have occurred largely without question, possibly
due to the support of European bodies. Spectrum managers have used a
number of arguments to make their case, some of which, when analyzed,
appear unconvincing, others of which may have substance and merit fur-
ther investigation. The arguments against mandating, although generally
ideological, appear mostly valid.
Above all, spectrum managers have looked at GSM, which has been a
great success, and compared it to the U.S. cellular market and reached the
conclusion that mandating a standard provides Europe with a significant
competitive advantage. As argued in Sections B.2 and B.3, this view is
flawed and attempts to repeat the success of GSM, though mandating
additional standards are not guaranteed to succeed. GSM succeeded
because there was a strong user requirement for a standard mobile radio
system across Europe and the GSM standard met the user requirement. It
may have been that it did not need to be mandated to succeed, although
this would have depended upon the extent to which individual countries
would have tried to develop their own systems. The United States
failed not because they allowed a range of proprietary systems to use the
radio spectrum but because industry failed to agree on a common
standard.
Appendix B 361
Europe has taken a lead in cellular radio because of its strong research
base, early availability of radio spectrum for cellular applications, strong
standards-making body, and economic and topographic factors. It is now
starting to lose that edge as innovative CDMA technologies are intro-
duced in the United States and as the United States dominates the mobile
satellite arena. Its lead in cordless technology is being threatened by the
Japanese personal handiphone system, and its lead in paging is under
threat by the U.S. Flex system manufactured by Motorola, possibly due to
the fact that DECT and ERMES are not well aligned with user require-
ments. Arguably, mandated standards is reducing the ability of Europe to
react to user needs and to provide competitive systems.
A factor that has been noted by many as of overriding importance is
the openness of the standard. Fundamentally, this does not appear to be
affected by whether the standard is mandated but by the standards-
making process. For this reason, openness has not been considered in
detail in this appendix.
In summary, it would appear that there are arguments for and against
mandating, most of which require further investigation to determine
whether they are valid.
B.5 Conclusions
This appendix raises some of the issues associated with the mandating of
particular standards when licensing an organization to provide a particu-
lar service. The practice of mandating seems widespread within European
governments and spectrum managers, despite their often heard claims
that they embrace free market ideals.
Of the arguments for and against mandating, the following views can
be summarized:
◗Mandating does not appear to materially affect the achievement of
economies of scale; it is the openness and appropriateness of stan-
dards that achieves this.
◗Mandating may actually hinder rather than help local industry.
◗Mandating does help roaming and may provide important societal
benefits.
362 The Complete Wireless Communications Professional
◗Mandating may hinder Europe maintaining its current lead in
mobile radio by preventing innovation.
◗Mandating may prevent the most spectrally efficient technologies
being adopted.
◗Mandating may help to achieve a single European market.
◗Mandating may be required to stimulate a market and prevent
manufacturers and consumers waiting for the winning standard to
emerge.
◗Mandating is contrary to a free market approach.
◗Mandating may decrease consumer choice.
A number of case studies were discussed that appeared to indicate
that standardization can be helpful, but for the best advantage, standards
should not be mandated. It was also noted that mandating may be reduc-
ing the level of innovation within European mobile radio industry, may
be preventing the most technically efficient use of spectrum (and possibly
reducing the economic benefit to the country), and may be contrary to
free trade ideals.
References
[1] Porter, M., The Competitive Advantage of Nations, London: MacMillan Press,
1998.
Appendix B 363
Glossary
AbS Analysis by synthesis. A type of speech coding where an attempt
is made to model the vocal tract of the speaker in order to reduce the
information needed to be transmitted.
ADPCM Adaptive Differential Pulse Code Modulation. A relatively
simple form of speech coding using a differential form of PCM.
ADSL Asymmetric digital subscriber line. A means of achieving high
data rates on twisted copper pair telephone wires and capable of provid-
ing up to 8 Mbps from the network to the subscriber and a few 100 kbps in
the reverse direction.
Allocation The process in spectrum management of determining the
purpose for which a piece of spectrum should be used.
AM Amplitude modulation. The modulation of the amplitude of a
carrier wave in accordance with the information to be transmitted.
AMPS Advanced Mobile Phone Service. An analog phone standard
in widespread use in North and South America.
AMR Advanced multirate speech coder. A proposal for a new speech
coder for GSM which would vary its coding rate in accordance with the
information to be transmitted.
365
ANSI American National Standards Institute. The U.S. body responsi-
ble for setting standards.
ARIB Association of Radio Industries and Businesses. The Japanese
body responsible for setting standards.
ARQ Automatic repeat request. An error correction technique
whereby blocks that are determined to be in error are resent.
ASCI Advanced speech call items. The additions to the GSM standard
that will provide group and broadcast calls.
Assignment The process in spectrum management of deciding
which user should be able to use a particular piece of radio spectrum.
ATIS Alliance for Telecommunication Industry Solutions. The U.S.
body responsible for the standardization of GSM-based solutions for use
in the United States.
ATM Asynchronous transfer mode. A technique for the transmission
of data over fixed networks where the transmitter and the receiver are
not synchronized.
AuC Authentication center. The entity within GSM that authenti-
cates the mobiles and provides a key for encryption purposes.
Autocorrelation The process of multiplying a sequence by a copy of
itself, when the copy is delayed by a variable time.
AVL Automatic vehicle location. The technique of determining the
position of a vehicle.
Back-to-back Transmission from one mobile directly to another
without using base stations.
BCCH Broadcast control channel. The channel within GSM that pro-
vides information on the configuration of the cell.
BCH Bose-Chaudhuri-Hocquenghem. A type of block coding error
correction.
BDT Bureau for the Development of Telecommunications. Part of
the ITU.
366 The Complete Wireless Communications Professional
Beauty contest A technique for deciding to whom to assign a license
by considering the relative merits of a number of competing bids.
Bent pipe A term used in satellite systems where any signal received
by the satellite is immediately rebroadcast back to the Earth station under
the satellite.
BER Bit error rate. The percentage of bits in error when transmitted
through a channel.
BOT Build, operate, and transfer. The act of a third party building a
network, starting to operate the network, and then transferring the net-
work to the owner.
BPSK Binary phase shift keying. A type of modulation where there
are only two possible constellation points and the phase of the carrier is
changed in order to move between constellation points.
BRA Basic rate access (ISDN at 144 kbps). A type of ISDN provision
where the user is given two 64-kbps bearer channels and a 16-kbps data
channel.
BSC Base station controller. The entity within GSM responsible for
controlling the base stations.
BSS Base station subsystem. A term for the combination of BTSs and
BSCs within the GSM network.
BT Bandwidth-time product. A measure of the amount by which a
pulse is distorted prior to modulation where a low BT product results in
a low transmitted bandwidth but spreading of the input pulses over a
number of transmitted data symbols.
BTS Base transceiver station. The entity within GSM responsible for
the transmission of radio signals.
Busy hour The hour during the day when there is the most traffic on
the network.
CAMEL Customized applications for mobile network enhanced
logic. An addition to the GSM standard allowing support for operator-
specific features for roaming mobiles. To do this, intelligent network prin-
ciples are being introduced into the network.
Glossary 367
CBS Common base station. The use within PMR of a base station
shared between a number of users.
CCIR Consultative Committee for International Radio. The previous
name for the ITU-R.
CCIT Consultative Committee for International Telegraphy. The pre-
vious name for the ITU-T.
CCITT Central Committee for Telephony and Telegraphy. The previ-
ous name for the ITU.
CCS Common channel signaling. The sending of signaling informa-
tion on the same fixed line as voice information. The signaling is normally
carried out of band.
CCSC Control channel system codeword. The signaling used within
the MPT1327 standard to identify mobiles or groups of mobiles.
CDMA Code division multiple access. The division of radio spectrum
by the provision of a different code to each of the users.
CELP Code excited linear prediction. A type of speech coding where
excitation sequences are selected from a codebook and those most accu-
rately describing the block of speech sent to the receiver.
CEPT European Conference of Postal and Telecommunications
Administrations. The European spectrum manager.
CIR Committed information rate. The rate that packet-based fixed
network protocols guarantee to provide to a particular user.
Clearance The act of a spectrum manager of removing existing users
from the radio spectrum so that it can be allocated to a new use.
Clipping The loss of the first syllable of each burst of speech due to the
delay in the speech activity detector identifying that a user has started
speaking.
CMIP Common management information protocol. The protocol
used by TMN.
368 The Complete Wireless Communications Professional
CT-2 Cordless telephony system 2. A digital cordless telephone sys-
tem, now generally being replaced by DECT.
CTCSS Continuous tone-controlled signaling system. A system used
in simple PMR radios to identify the group to which the call is destined
through the continuous transmission of low-frequency audio tones.
D-AMPS Digital AMPS. A digital cellular standard mainly in use in
North and South America, also known as IS-136 and TDMA.
DCA Dynamic channel allocation. A system whereby base stations do
not have dedicated channels but select a channel when it is needed for
communications on the basis of the channels currently suffering the low-
est interference. As a result, system capacity is typically increased.
DCS Digitally controlled squelch. A system used in PMR where the
mobile’s speaker is turned off unless there is a signal from the network
activating the mobile.
DCS1800 Digital cellular system at 1,800 MHz. A digital system based
on GSM and operating at 1,800 MHz. This has been renamed GSM1800.
DECT Digital enhanced cordless telephone. A cordless standard now
widely deployed around the world.
DPSK Differential phase shift keying. A modulation technique where
the transmitted information is encoded through the phase difference
between the previous and current symbols.
D-QPSK Differential quadrature phase shift keying. A modulation
technique where the transmitted information is encoded through the
phase difference between the previous and current symbols and there are
four possible symbol points.
DS Direct sequence. A form of CDMA where the input data is multi-
plied by a code.
DSL Digital subscriber line. A technique to enhance the data
rates that can be sent down copper lines using advanced modulation
techniques.
Glossary 369
DSRR Digital short-range radio. A standard for short-range radio sys-
tems providing back-to-back communications, which has been
unsuccessful.
DTI Department of Trade and Industry. Part of the U.K. government.
DUP Data user part. A protocol within SS7 responsible for the trans-
mission of data.
EBIT Earnings before interest and taxation. An accounting measure
that details the profit before interest and taxation are deducted.
EBRD European Bank for Reconstruction and Development
EC European Commission
ECM Explicit congestion message. A message sent in packet-switched
fixed network protocols to warn the information source to reduce the rate
of the transmitted data.
EFR Enhanced full-rate speech coder. A new GSM speech coder
working at the same data rate as previous coders but providing a better
voice quality.
EIR Equipment identity register (when used in conjunction with
mobile networks). A register within GSM that keeps a record of stolen
mobiles so that they can be barred from use on the network.
EIR Excess information rate (when used in conjunction with fixed
networks). An agreed data rate set within ATM networks at which infor-
mation can be transmitted in the case that the network is not congested.
EIRENE European Integrated Radio Enhanced Network. The Euro-
pean railway project to provide a digital mobile radio system.
EMLPP Enhanced multilayer priority and preemption. The addition
of priority and preemption capabilities to the GSM standard.
ERMES European Radio Messaging Service. A standard for digital
paging systems.
ETSI European Telecommunications Standards Institute. The
European body responsible for standardizing telecommunication
systems.
370 The Complete Wireless Communications Professional
FACCH Fast associated control channel. The channel used within
GSM to send signaling information to the user in the case that more sig-
naling information than can be accommodated on the SACCH is required.
Transmission of FACCH information results in stealing speech frames.
Fade The loss, or significant reduction, in radio signal in a particular
location.
Fast fading The term given to a mobile radio propagation phenom-
ena whereby the mobile experiences many fades per second. Fast fading
is caused by multipath propagation.
FCC Federal Communications Commission. The U.S. body responsi-
ble for the management of radio spectrum for non-governmental use.
FDM Frequency division multiplexing. The division of the input data
stream into a number of substreams that are then sent on separate mobile
radio channels.
FDMA Frequency division multiple access. The division of the mobile
spectrum into a number of frequency blocks that users access when they
require a channel.
FE Functional entity. A part within the IN that is responsible for per-
forming a particular function.
FEA Functional entity action. The action performed by a FE.
FFSK Fast frequency shift keying. A type of modulation where the
frequency of the carrier is changed in accordance with the information
transmitted by the minimum amount required to ensure the signal is cor-
rectly decoded.
FH Frequency hopping. The changing of frequency during the
process of transmission, often hundreds of times per second, in order to
evenly distribute interference and overcome fading.
Free space attenuation The loss that a signal experiences as a result
of traveling through free space. It is proportional to the distance squared.
Fresnel zone An area around a LOS path that must remain clear if
the signal is not to suffer significant attenuation.
Glossary 371
GAP Generic Access Protocol. Part of the DECT specification that
ensures mobiles will be able to roam from one network to another.
GDP Gross Domestic Product. The value of the business conducted
within a country.
GMSC Gateway mobile switching center. An entity within GSM that
forms the interface between a GSM network and other networks.
GMSK Gaussian minimum shift keying. A form of phase modulation
where the input data is shaped by a filter having a Gaussian impulse
response prior to transmission.
GPRS General packet radio service. An addition to the GSM standard
that allows the transmission of packet data.
GPS Global Positioning System. A system allowing receivers to locate
themselves to an accuracy of 100m or better. The system works by meas-
uring the received signals from a number of satellites.
GSM Global system for mobile communications. The most successful
digital cellular system in the world.
HDSL High-speed digital subscriber line. A subset of the DSL family
where symmetric data rates of up to 2 Mbps are provided using up to three
parallel copper pairs.
HDTV High-definition TV. A form of TV where a higher definition
picture than normal is transmitted.
HFC Hybrid fiber coax. A design technique used in cable networks
where fiber optic cables are used in the backbone and coaxial cable in the
last mile drop to the subscribers.
HLR Home location register. The entity within GSM that stores the
last known location of the subscribers to the accuracy of an MSC area.
HSCSD High-speed circuit-switched data. An enhancement to the
GSM standard whereby users can concatenate a number of timeslots to
obtain data rates of up to 64 kbps.
IEE Institute of Electrical Engineers. The U.K. professional body rep-
resenting electronic and electrical engineers.
372 The Complete Wireless Communications Professional
IEEE Institute of Electrical and Electronic Engineers. The U.S. profes-
sional body representing electronic and electrical engineers.
IMEI International mobile equipment identity. The number used
within GSM to identify the mobile phone that is being used to make the
call.
IMSI International mobile subscriber identity. The number used
internally within GSM to identify the subscriber who is making the call.
This number is derived from the dialed number, the MSISDN during the
call initiation process.
IMTS Improved Mobile Telephone Service. An early analog phone
service deployed in the United States.
IN Intelligent network. The concept of adding a capability to program
a fixed phone network so that new services can be readily added without
needing to upgrade the hardware. The concept also includes an architec-
ture design that can realize this capability.
INAP Intelligent network application part. A protocol used within
the SS7 signaling system for the support of IN.
IOU Intelligent overlay underlay. A technique used within GSM to
enhance the capacity of a network by deploying carriers in a cell with dif-
ferent transmit powers and different reuse patterns.
IP Intelligent peripheral. An entity within IN responsible for gather-
ing information from and supplying information to the user.
IPO Initial public offering. The first sale of shares in a company onto
the stock market.
IPR Intellectual property right. A patent or similar protective distin-
guishment that gives the inventor rights to exploit their invention with-
out others copying it.
IRR Internal rate of return. An accounting measure of the effective
interest rate that would have to be available from a bank in order to pro-
vide the same return on investment as the project under consideration.
Glossary 373
ISDN Integrated services digital network. A network protocol for
fixed networks that provides digital transmission for users in multiples of
64 kbps.
ISI Intersymbol interference. A propagation phenomena whereby a
signal containing the previous bit, or symbol, transmitted, is sufficiently
delayed that it interferes with the current bit or symbol.
ISM Industrial scientific and medical. A category of use of radio spec-
trum whereby the spectrum is not used for communications but for pur-
poses such as microwave heating.
ISUP Integrated services user part. Part of the SS7 signaling system
protocol responsible for carrying ISDN data.
ITU International Telecommunications Union. The worldwide body
responsible for spectrum management.
LAN Local area network. A communications network, often fixed,
that provides communications between a small group of users in the same
building or on the same campus.
LEO Low Earth orbit. A satellite orbit between 500 km and 1,000 km
above the surface of the Earth, used by the new generation of personal
communication satellites.
Limited mobility The ability of the user to make a call on a mobile
phone but only within a restricted area, often covering a single city.
LMDS Local multipoint distribution system. A TV transmission sys-
tem using radio propagation at around 28 GHz. It is also being proposed
for wideband data transmission.
Long code A code used within the cdmaOne system that is assigned
to a particular user to distinguish them from other users.
LOS Line of sight. A form of radio propagation where it is possible for
the receiver to visually see the transmitter.
LTP Long-term predictor. Part of a speech coder that provides infor-
mation about relatively long-term variations in the speech waveform.
MAP Mobile application part. Part of the SS7 signaling protocol used
to support GSM signaling between BSC, MSC, and location registers.
374 The Complete Wireless Communications Professional
MBA Master of Business Administration. An academic degree in
business management.
MCCH Main control channel. The name of the control channel used
within TETRA.
MLPP Multilevel priority and preemption. The name of the priority
and preemption scheme used within ISDN.
MMDS Microwave multipoint distribution system. A type of TV
distribution system using analog transmission and working in the
2.5-GHz band, providing one-way transmission only.
MOS Mean opinion score. The score given to a speech coder by a
panel of listeners to rate its ability to accurately encode and decode voice.
MPE Multipulse excited. A form of speech coder where the excitation
waveform is represented by multiple pulses.
MSC Mobile switching center. The entity within a GSM network
responsible for switching all calls.
MSISDN Mobile station integrated services digital number. A mobile
number used within GSM as the number dialed by users who wish to con-
tact a mobile.
MSK Minimum shift keying. A type of phase modulation whereby
the phase of the carrier is only changed by half a cycle, in a linear manner,
over a bit period.
MTP Message transfer part. A part of the SS7 protocol responsible for
the accurate transmission of messages across the network.
MTS Mobile Telephone Service. An early form of mobile radio system
deployed in the United States in 1946.
MVDS Microwave video distribution system. A type of TV distribu-
tion system standardized across Europe, working at 40 GHz and providing
a large number of TV channels on the downlink with some limited return
path capability.
NMT Nordic Mobile Telephone. An analog mobile phone standard
used widely in Scandinavia at 450 MHz and 900 MHz.
Glossary 375
NPV Net present value. An accounting measure used to determine
the profit from a project after discounting future cash flows by the oppor-
tunity cost of capital.
ODMA Opportunity driven multiple access. A scheme whereby
mobiles who hear a message destined for another mobile can retransmit
this message if the other mobile is out of reach of a base station.
OFDM Orthogonal frequency division multiplexing. A category of
FDM where the subchannels used for transmission are orthogonal to one
another.
OMAP Operations and maintenance application part. Part of the SS7
signaling protocol responsible for passing messages to the operations and
maintenance center.
OMC Operations and maintenance center. The part of a mobile or
fixed network that monitors the operation of the network for faults and
can modify the parameters of remote parts of the network, such as the fre-
quency at which a particular base station transmits.
OnePhone A concept developed by BT whereby users have a dual-
mode DECT/GSM phone that selects the DECT standard when indoors
and the GSM standard when out of doors.
O-QPSK Offset quadrature phase shift keying. A type of QPSK where
the change between symbols on one of the quadrature branches is offset
by half a symbol period compared to the other branch to avoid the trans-
mitted wave form passing through the origin during a change of symbol.
O&M Operations and maintenance. Another term for the OMC.
PABX Public access branch exchange. A switch in a fixed network.
PAMR Public access mobile radio. A type of PMR where the network
is provided by a third party, or operator, and shared between a number of
users.
PBX Private branch exchange. A small switch within an office provid-
ing service to the users in the office, allowing interoffice calls, and
providing a point of interconnection with the PSTN.
376 The Complete Wireless Communications Professional
PCM Pulse code modulation. A simple voice-coding technique using
regular samples to provide a digital datastream at 64 kbps.
PCS Personal communications service. Another name for digital cel-
lular operators, particularly applied to operators in the United States with
spectrum at 1,900 MHz.
PDC Personal digital cellular. The Japanese digital cellular standard.
PDH Plesiochronous digital hierarchy. A technique used in fixed net-
works to communicate between switches running at different clock
speeds by a process of multiplexing and demultiplexing.
PEST Political, economic, social, and technological. An acronym used
by management when conducting brainstorming sessions to set strategy.
PHS Personal handiphone system. A Japanese cordless standard.
Pilot Tone A signal sent at a constant power level which allows
mobiles to detect the presence of carriers.
PLMN Public land mobile network. The normal term for a mobile
network such as that operated by a mobile radio operator.
PM Phase modulation. The modulation of the phase of the carrier
wave in accordance with the information to be transmitted.
PMR Private mobile radio. A use of radio systems where the user pro-
vides their own infrastructure. There is a complete industry with different
mobiles and infrastructure to support this particular mode of operation.
PN Pseudorandom noise. A type of mathematical sequence with par-
ticular properties such that the signal is very close in appearance to ran-
dom noise.
PRA Primary rate access. The provision of 30 data channels each pro-
viding 64 kbps within ISDN.
PRMA Packet reservation multiple access. A type of access whereby
users only transmit when they have information to send and the network
reserves them resource for the duration of their transmission.
PSTN Public switched telephone network. The normal name for a
fixed telephone network such as that operated by the PTO.
Glossary 377
PTO Post and Telecommunication Organization. The normal term for
the company that operates the main PSTN within country. The PTO is
state-owned in some countries.
QAM Quadrature amplitude modulation. A type of modulation
where both the phase and the amplitude of the transmitted signal is var-
ied in accordance with the information to be transmitted.
QPSK Quadrature phase shift keying. A type of modulation where
the phase is varied in accordance with the information to be transmitted
and can take one of four discrete values.
Quantization error The difference between the original waveform
and the waveform after digitization has occurred.
RA Radiocommunications Agency. The body in the United Kingdom
responsible for the management of radio spectrum.
Rain Fading The reduction in signal strength during heavy rain as a
result of absorption of the radio signal by the moisture in the atmosphere.
RC Raised cosine. A form of pulse shaping whereby a cosine segment
is fitted to the leading and falling edges of the pulse.
RF Radio frequency. The term for operations and components that act
at the carrier frequency.
RFQ Request for quotation. A document sent out, often by an opera-
tor, requesting quotations from suppliers.
RMS Root mean square. A mathematical measure derived by taking
the square root of the average of the squared input data.
RPE Regular pulse excited. A form of AbS speech coding whereby the
coder is excited by a regular stream of pulses.
RPE-LTP Regular pulse excited—long-term prediction. A form of
RPE speech coder where a long-term predictor is used to further remove
the redundancy in the voice signal.
RS Reed Solomon. The name of a type of block coding scheme.
RX-QUAL Received signal quality. A measure of the quality of the
received signal in a GSM system.
378 The Complete Wireless Communications Professional
SACCH Slow associated control channel. A channel within the GSM
system used to send signaling information to and from the mobile while
they are on a call.
Sampling rate The frequency at which the input waveform is
sampled.
SCH Synchronization channel. A channel within the GSM control
channels that is used to allow the mobiles to synchronize to the framing
structure.
SCCP Signaling connection and control part. A protocol within the
SS7 signaling system used to provide a virtual connection and context for
transmissions.
SCP Service control point. An entity within an IN that controls the
service provided to the users.
SDH Synchronous digital hierarchy. A type of fixed network where
all the switches are working in synchronization.
SELCALL Selective calling. A type of signaling message sent at the
start of a PMR broadcast that only alerts those for whom the call is
destined.
SFN Single frequency network. A technique used within digital TV
where all the cells broadcast on the same frequency and a form of equal-
izer within the receiver removes any echoes.
SIB Service-independent building block. A concept within IN
whereby the components of the service offered to the users are identified
at a level not specific to a particular network.
SIM Subscriber Identity Module. A card within the GSM system that
carries the identity of the subscriber. By being placed in a different phone
it can allow subscribers to easily change phone but keep the same
number.
SIR Signal-to-interference ratio. The difference between a wanted
signal and an interfering signal.
SME Small- or medium-sized enterprise. This is typically defined as
companies with less than 200 employees.
Glossary 379
SMG Special mobile group. The group within ETSI that conducts
GSM standardization.
SMR Specialized mobile radio. The name given to PMR within the
United States.
SMS Short message service. The ability within GSM to send text mes-
sages of up to 160 characters in length to a mobile.
SNR Signal-to-noise ratio. The difference between the wanted signal
and the noise.
SONET Synchronous optical network. A network linked using opti-
cal fiber with all entities operating synchronously.
Squelch A function within PMR of not allowing the signal to activate
the loudspeaker if it falls below a certain level that is normally set by the
user using a rotary knob.
SRBR Short-range business radio. The name given by Motorola to a
simple radio system that provides back-to-back communications.
SSP Service switching point. An entity within an IN that provides the
switching function.
SS7 Signaling system number 7. A protocol for sending information
over a fixed network.
Switching in space The addition of switching capability to a satellite
system so that calls can be passed from one satellite to another until they
are over the Earth station closest to their destination.
SWOT Strengths, weaknesses, opportunities, and threats. An acro-
nym used by managers when brainstorming strategy in order to consider
all important issues.
TACS Total Access Communications System. An analogue cellular
radio system widely deployed within Europe.
TC Technical committee. A committee set up within ETSI to study a
particular issue.
380 The Complete Wireless Communications Professional
TCAP Transaction capability application part. Part of the SS7 protocol
that links separate messages together into a context so that discrete
responses can appear to be answers to a specific request.
TCM Trellis Code Modulation. An advanced form of encoding
whereby modulation and error correction are linked together in a means
that enhances the information rate that can be transmitted.
TCP/IP Transport control protocol/Internet protocol. The protocol
used for transmission over the Internet.
TD-CDMA Time division—code division multiple access. A combi-
nation of TDMA and CDMA.
TDD Time division duplex. The transmission of uplink and downlink
on the same frequency but at different times.
TDMA Time division multiple access. A multiple access technique
whereby users are given access to all the bandwidth but for a limited time.
TETRA Terrestrial trunked radio. A standard for digital PMR radio
systems.
TIA Telecommunications Industry Association. The U.S. body
responsible for telecommunications standardization of most systems,
with the exception of GSM1900.
TMN Telecommunications management network. A concept cover-
ing all fixed and mobile telecommunications networks whereby the same
OMC can be used across a wide range of equipment by standardizing the
OMC interface.
TRAU Transcoder and Rate Adaption Unit. The entity within GSM
responsible for transcoding voice and for adapting the rate of data to be
transmitted, if required.
Trombone A name for the route followed by some international calls
within GSM where the call passes to the home country and back again in
a long loop.
Trunking gain The gain in efficiency of use of radio channels that
results when a large number of channels are placed together in a pool.
Glossary 381
TRX Transmitter receiver. The name within GSM for the entity
within the base station responsible for transmitting and receiving the
signal.
TUP Telephone user part. The part of the SS7 protocol responsible for
simple speech communications.
UHF Ultra High Frequency. The use of radio frequencies between
300 MHz and 3 GHz.
UIC Union Internationale des Chemins de Fer (European Railway
Union). The official body responsible for the harmonization of railway
systems across Europe.
UMTS Universal mobile telephone service. The European concept for
the next generation of mobile radio systems to be deployed around the
year 2002 onward.
USP Unique selling point. A management term for the unique feature
offered by their product or service.
VBS Voice broadcast service. The addition to the GSM standard to
provide broadcast capabilities.
VDSL Very high-speed digital subscriber line. A form of DSL that will
operate over distances of less than 100m but provide data rates of up to
50 Mbps in both directions.
VGCS Voice group call service. The addition to the GSM standard to
provide group calls.
VLR Visitors’ location register. The entity within GSM that is coupled
to each MSC and stores the location of each mobile to the accuracy of a
location area.
VSAT Very small aperture terminal. A satellite terminal that commu-
nicates with geostationary satellites and has a dish diameter of less than
2m. Most VSATs are much smaller than this and can fit into briefcases.
W-CDMA Wideband code division multiple access. A form of CDMA
where the bandwidth of the transmitted signal is around 5 MHz.
Winner’s curse A problem that can occur in auctions whereby the
winner has overvalued the market and subsequently goes bankrupt.
382 The Complete Wireless Communications Professional
WLL Wireless local loop. A concept whereby fixed phones are pro-
vided using radio transmission.
xDSL Belonging to the family ADSL, HDSL, and VDSL.
XOR Exclusive OR mathematical operation.
Glossary 383
About the author
William Webb graduated from Southampton University with a first
class honors degree in electronic engineering and all top year prizes
in 1989. In 1992, he earned his Ph.D. in mobile radio and in 1997 was
awarded an MBA, all from Southampton University, United Kingdom.
From 1989 to 1993, William worked for Multiple Access Communi-
cations Ltd. as the Technical Director in the field of hardware design,
modulation techniques, computer simulation, and propagation model-
ing. In 1993, he moved to Smith System Engineering Ltd., where he was
involved in a wide range of tasks associated with mobile radio and spec-
trum management including devising the U.K. spectrum pricing propos-
als and writing the modifications to the GSM standard to introduce group
and broadcast calls. In 1997, he moved to Netcom Consultants where he
led the Wireless Local Loop division, and in 1998 he moved to Motorola
where he is responsible for the Wireless Local Loop and In-Building
products.
Dr. Webb has published over fifty papers, holds four patents, was
awarded the IERE Premium in 1994, is a member of the IEE where he sits
on the Editorial Advisory Panel, and is a senior member of the IEEE. He is
the coauthor, with L. Hanzo, of Modern Quadrature Amplitude Modulation
(Wiley and Sons, New York, 1992) and the author of Introduction to
Wireless Local Loop and Understanding Cellular Radio, both published by
Artech House, 1997.
385
Index
Index
π/4DQPSK, 106, 124
A
Accounting, 211–22
balance sheet, 215–18
first pass modeling and, 221–22
funds flow statement, 218–20
introduction to, 211
profit and loss, 212–15
Advanced Communications
Technologies (ACTS)
program, 348
Advanced Mobile Phone Service
(AMPS), 9
Advanced multirate coder (AMR)
coder, 45
Advanced speech call items
(ASCI), 271–72
Aeronautical radio, 158
Alliance for Telecommunications
Industry Solutions
(ATIS), 302
Alpha proposal, 275, 276
Ambulance services, 266–67
American National Standards
Institute (ANSI), 303
Amplitude modulation (AM), 58
defined, 56
quadrature, 62–63
waveform illustration, 57
See also Modulation
Analog-to-digital converter, 38
Analysis by synthesis (AbS), 42
codecs, 44
defined, 42
encoder illustration, 43
APCO25, 13, 125
Association of Radio Industries and
Businesses (ARIB), 300
Asynchronous transfer mode
(ATM), 80, 176–78
defined, 176
design uses, 177
fixed-size packets, 178
OSI layered protocol, 176, 177
Auctions (radio spectrum), 291–94
English, 291
multiple English, 292–93
multiple object, 292
PCS, 293–94
387
Auctions (radio spectrum)
(continued)
sealed bid first-price, 291–92
second-price sealed bid, 292
simple, 291
“winner’s curse,” 294
See also Radio spectrum
Authentication center (AuC), 90
Auto-correlation properties, 74, 75
Automatic vehicle location
(AVL), 267
B
Balance sheet, 215–18
defined, 215
goal of, 216
illustrated, 216–17
See also Accounting
Bandwidth
increasing, 246
reducing, 246
TETRA requirement, 315
Bandwidth-time (BT) values, 61
Baseband hopping, 249
Base station
controllers (BSCs), 88
costs, 226
identity code (BSIC), 100
subsystem (BSS), 88, 89
Base transceiver stations (BTSs), 88
Bill generation, 243
Binary phase shift keying (BPSK), 56
constellations, 64
performance comparison, 59
Bit error rate (BER) threshold, 68
Block codes, 49
Block interleavers, 51
Broadcast control channel
(BCCH), 97
Bureau for the Development
of Telecommunications
(BDT), 283
Bursts
contents of, 98–99
structure, 98
Business case, 223–37
defined, 223
financing, 233–35
network costs, 223–26
operating expenses, 227
revenue, 227–33
structure, 223
summary, 235–37
See also Mobile radio networks
C
Cable TV systems, 140–41
Capacity enhancement, 246–53
introduction to, 246
techniques, 246–47
when to use, 252–53
Carrier recovery, 66–68
decision-directed, 67–68
problem, 67
requirement, 66
times-n, 67
Carrier-to-interference (C/I), 315
CCITT7 protocol, 174–75
application support, 174
CCCP, 167
defined, 172
INAP, 167–68
MAP, 174, 175
TCAP, 167
user parts, 174
See also Protocols
CdmaOne, 14, 101–5, 323
capacity, 105
channels, 102
388 The Complete Wireless Communications Professional
defined, 101–2
downlink transmission, 102, 103
handoff, 105
uplink transmission, 103–4
CDMA vs. TDMA, 322–27
background, 322–23
capacity of, 323–25
debate analysis, 327
issues, 325–27
Cells
adjacent, measurements
of, 99–100
capacity planning, 193
cluster of, 33
concentric, 247, 249, 253
coverage requirement, 194
defined, 33–34
macrocells, 252, 326
microcells, 198–99, 251–52,
253, 326
names, 34
picocells, 198–99
size of, 198–99
splitting, 247
underlay/overlay, 247
using more, 247, 251–52
Cellular systems, 85–106, 142
cdmaOne, 101–5
choice of, 111–14
comparing, 87
GSM, 88–101
IS-136, 106
PMR vs., 261–63
range of, 85–88
standards, 86
technical parameters, 87
technologies, 85–106
WLL vs., 142–43
See also Mobile radio
CEPT, 285
defined, 10
standardization, 11
Channels
control, 94–101
DECT, 133
imperfections, overcoming, 48–55
MPT1327 standard, 118
number of required, 36
paging, 102
synchronization, 102
traffic, 35, 93, 95–96
Circuit-switched transmission, 79
Clock recovery, 64–66
early-late, 65–66
requirement, 65
synchronizer, 66
times-two, 65
types of, 65
zero-crossing, 66
Clusters
decreasing size of, 247
illustrated, 33
repeated, 35
size of, 34
Code division multiple access
(CDMA), 14
autocorrelation curve, 76
breathing problems, 326–27
codewords, 72, 73, 74, 76
cost, 326
defined, 69
despreading process, 75
frequency planning, 325
inefficiency, 324
interference distribution, 324–25
macrocell/microcell, 326
markets, 326
power control error sensitivity, 77
power control systems, 77–78
range, 325
risk, 326
roaming, 326
signal recovery, 75
spreading process, 73
Index 389
Code division multiple access
(CDMA) (continued)
spreading result, 74
See also CDMA vs. TDMA;
Multiple access
Code excited linear prediction
(CELP) coders, 44
design of, 45
structure, 45
Coders
AbS, 42, 43
AMR, 45
CELP, 44–45
speech, 40
variable rate, 46
Codewords, 72, 73, 74, 76
Committed information rate
(CIR), 176
Common base station (CBS), 116
Concentric cells, 247, 249, 253
Conference Europeenne des
Administrations des Postes
et Telecommunications.
See CEPT
Conferences, 340–46
benefits of appearing at, 340
chairing, 343–44
getting invited to, 340
papers, writing, 345–46
presentation, giving, 342–43
presentation preparation, 340–42
Conflict, 311–28
CDMA vs. TDMA, 322–27
DECT vs. PHS, 319–22
handling, 327–28
introduction to, 311–12
TETRA vs. GSM, 313–19
Continuous tone-controlled signal
system (CTCSS), 115–16
subaudio tones, 115
variation, 116
Control channels, 94–101
broadcast (BCCH), 97
fast associated (FACCH), 99
frequency (FCCH), 102
helping mobile find, 97
key functions, 94
MPT1327, 118
PHS, 135
slow associated (SACCH), 94, 124
See also Channels
Control channel system codeword
(CCSC), 118
Convolutional codes, 49
Cordless systems, 128–35, 142
DECT, 130–34
defined, 127–28
as limited mobility cellular
system, 129–30
overview, 128–30
PHS, 134–35
within home, 128–29
within office, 129
See also Mobile radio
Corporate strategy, 332–38
defined, 332
development of, 332
five-forces model and, 334–35
inappropriate, 338
mission statement, 337
PEST and, 333
price/quality and, 336–37
start of, 332–33
statement of strategy, 337
SWOT and, 333–34
value chain and, 335–36
Costs
base station, 226
hardware, 225
interconnection, 229
network, 223–26
subscriber unit, 223–25
switching, 226
Coverage requirements, 294–95
390 The Complete Wireless Communications Professional
Customer care, 243–44
Customized applications for
mobile network enhanced
logic (CAMEL), 272–73
D
D-AMPS++, 274
Data link control (DLC), 134
Decision-directed carrier
recovery, 67–68
Decision making, 331
Decoders
speech, 41
Viterbi, 50, 54, 55
Decoding, 52–55
DECT/GSM integration, 182–83, 273
DECT vs. PHS, 319–22
background, 319
claims, 320
debate analysis, 321–22
key issues, 319–21
Delay
adding, 51
complete bit period, 31
one-fourth of bit period, 30
probability of, 37
three-fourth of bit period, 30
Delta scheme, 276
Depreciation, 214–15
Differential coding, 67
Diffraction loss variation, 28
Digital enhanced cordless telephone
(DECT), 10, 11, 130–34
capacity, 320
case study, 361
channels, 133
data link control (DLC), 134
delay, connection, power
consumption, 321
error control, 134
framing structure, 131
infrastructure cost, 320–21
interworking with GSM, 321
introduction, 130–31
medium access control
(MAC), 132–34
physical layer, 131–32
provision of 64-kbps bearers, 321
provision of repeaters, 321
simplicity of planning, 321
See also Cordless systems; DECT
vs. PHS
Digitally controlled squelch
(DCS), 116
Digital short-range radio
(DSRR), 12–13
case study, 360
scope, 12
Digital TV, 141
Discontinuous transmission, 247
Distribution channels, 297
Dual-band operation, 246
Dynamic channel allocation
(DCA), 132, 249–50
defined, 249
maximum practical gain, 250
E
E1 carriers, 170, 171
Early-late clock recovery, 65–66
Earnings before interest and taxation
(EBIT), 215
Economics, 333
of mobile radio networks, 211–37
satellite system, 153–54
TETRA vs. GSM, 315–18
value analysis, 289
Emergency services, 266–67
Encoders
AbS, 43
Index 391
Encoders (continued)
convolutional, 49–50
parametric, 40
Encoding, 49–52
English auctions, 291, 292–93
Enhanced full-rate coder, 247, 273
Entrepreneurship, 330
Equipment identity register (EIR), 90
Equipment manufacturers, 208–9
Erlangs
channels vs., 36
defined, 34
Erlang B formula, 34, 35, 37
Erlang B macro, 351
Erlang C formula, 36, 37
Error correction systems, 49
Error rates, 49
Error-weighting filter, 43
ESTI, 11
European Bank for Reconstruction
and Development
(EBRD), 234
European Commission (EC), 10
European Radio Messaging Service
(ERMES), 290
European Telecommunications
Standardization Institute
(ETSI), 11, 276
defined, 300
members, 302
project team (PT), 301
SMG, 300–301
standards availability, 302
standard stages, 304–5
structure, 301
technical committee (TC), 300
See also Standards
Excess information rate (EIR), 176
Explicit congestion messages
(ECMs), 176
F
Fading
defined, 21
frequency selective, 31
phenomenon, 22
Rayleigh, 22–28
slow, 21–22
Fast associated control channel
(FACCH), 99
Fast fading. See Rayleigh fading
Fast frequency shift keying
(FFSK), 118
Federal Communications
Commission (FCC), 9
Filters, raised-cosine (RC), 59
Financing, 233–35
defined, 233
options, 233
shareholder, 235
vendor, 234
See also Business case
Five-forces model, 334–35
areas, 334–35
defined, 334
illustrated, 334
Fixed link usage, 158
Fixed mobile convergence
(FMC), 178–87
advanced network convergence
solutions, 182–84
defined, 178
defining, 179
future of, 185–87
introduction, 178
mobile substitution
solutions, 184–85
network integration
solutions, 181–82
network overlay
solutions, 180–81
392 The Complete Wireless Communications Professional
solutions, 179–85
solution summary, 186
use by different parties, 179
Fixed/mobile integration, 295
Fixed networks
architectures, 162–69
intelligent, 165–68
interfacing with, 161–87
mobile convergence, 178–87
need for, 161–62
numbering/addressing plans, 169
outline, 162
protocols, 170–78
switch design, 162–65
TMN, 168–69
Frame relay, 175–76
Frames
hyperframe, 97
structure, 98
superframes, 97
Free-space loss, 21
Frequency control channel
(FCCH), 102
Frequency division multiple access
(FDMA), 13
cost disadvantage, 70
defined, 68
deployment, 69
inefficiency, 69
signal combining, 71
spectrum, 70
See also Multiple access
Frequency hopping, 247, 253
baseband, 249
defined, 248
synthesizer, 249
when to use, 253
Frequency modulation (FM), 58
defined, 56
waveform illustration, 57
See also Modulation
Frequency selective fading, 31
Funds flow statement, 218–20
calculation, 218
defined, 218
illustrated, 219–20
See also Accounting
G
Gateway mobile switching center
(GMSC), 90
Gaussian MSK (GMSK), 56
comparative performance, 59
comparative performance with
different BT values, 61
General packet radio service
(GPRS), 272
Gold codes, 75
Government policy, 294–97
coverage requirements, 294–95
distribution channels, 297
fixed/mobile integration, 295
number of mobile operators
and, 296–97
GSM, 10–12, 14, 88–101, 263, 265
advanced speech call items
(ASCI), 271–72
BSS, 88, 89
burst structure, 98
call routing, 92–93
CAMEL, 272–73
case study, 359–60
DECT handset integration, 273
enhanced full-rate codec
(EFR), 273
evolution, 271–74
frame structure, 98
framing format for control
purposes, 94–101
framing format for speech, 93–94
Index 393
GSM (continued)
full-rate speech codec, 45
general packet radio service
(GPRS), 272
handover, 92
high-speed circuit switched data
(HSCSD), 272
locating subscriber, 91
numbering scheme, 100–101
paging and random access, 91–92
for private users, 316
SIM toolkit, 273
spectrum, 70
spectrum efficiency, 101
success of, 10
switching system, 90
system architecture, 88–91
system overview, 89
technology evaluation, 313–15
transmission within, 93–101
wide area coverage, 314
See also TETRA vs. GSM
H
Half-rate coder, 246
Handoff, soft, 105
Handover, GSM, 92
Hata model, 196
Hertz, Heinrich, 4
High-speed circuit switched data
(HSCSD), 272
History
early, 4–7
milestones, 5
mobile radio milestones, 8–10
transistor and, 7
Home location register (HLR), 47
Human resource management, 331
Hyperframes, 97
I
Improved Mobile Telephone Service
(IMTS), 8
Industrial, scientific, and medical
(ISM) uses, 158
Information systems, 331
Initial public offering (IPO), 235
Integrated services digital network
(ISDN), 173–74
BRA, 173, 174
defined, 173
ISUP, 174
PRA, 173
Intelligent network application part
(INAP), 168
Intelligent networks (INs), 165–68
benefits, 165
conceptual model, 166
defined, 165
distributed functional plane, 166
functional model, 167
global functional plane, 166
physical plane, 166–67
service plan, 165–66
Intelligent peripheral (IP), 168
Intelligent underlay/overlay
(IUO), 249
Interconnection, 199–203
calculation example, 232
costs, 229
fee prediction, 230
leased link, 201
methods, 200–201
method selection factors, 200
microwave link, 201–2
parameters, 199–200
point-to-point overlay
networks, 202–3
satellite link, 203
Interexchange signaling
protocols, 172
394 The Complete Wireless Communications Professional
Interference
cross-border, 356
distributing, evenly, 248–50
mandated standards and, 355–56
reduction, 251
Interleavers, block, 51
Internal rate of return
(IRR), 235, 236–37
International management, 330
International mobile equipment
identity (IMEI), 101
International mobile subscriber
identity (IMSI), 101
Internet telephony, 139–40
Intersymbol interference (ISI), 20, 29
Iridium, 153
IS-136 standard, 106, 323
ITU
Council, 283
E.164 recommendation, 169
Plenipotentiary Conferences, 283
radio communication
conferences, 283–84
radio communications
assemblies, 284
Radio Regulations Board, 284
recommendations, 284–85
structure of, 282
L
Large users, 255–68
emergency services, 266–67
introduction to, 255–57
police, 263–66
railways, 257–63
working directly with, 256
Leadership, 331
Leased links, 201
License applications, 205–7
factors, 205–6
good, 207
government objectives and, 206
winning, 207
Line-of-sight (LOS) path, 26
Links
budget, 195
leased, 201
microwave, 201–2
satellite, 203
Local area networks (LANs), 130
Local multipoint distribution system
(LMDS), 141
defined, 147
technologies for, 144–49
Long-term predictor (LTP), 43
Low Earth orbit (LEO)
systems, 151–52
M
Macrocells, 252, 326
Management, 329–38
authority, delegation, and
decentralization, 331
of change, 331
corporate strategy and, 332–38
decision making, 331
human resource, 331
information systems, 331
international, 330
introduction to, 329–30
leadership and, 331
organizational structure and
behavior, 331
planning/strategic, 330
radio spectrum, 32, 282–87
strategy implementation, 330
theory, 330
Mandating standards, 353–63
case studies, 359–61
conclusions, 362–63
Index 395
Mandating standards (continued)
economies of scale and, 354
European roaming and, 355
free market approach and, 358
free-trade principles and, 359
implications, 361–62
innovation and, 358
interference and, 355–56
introduction to, 353–54
key issues, 354–59
product differentiation and, 359
spectrum efficiency and, 356
standard openness and, 356–57
support of European industry
and, 354–55
See also Standards
Marconi, Guglielmo, 6
Mean opinion score (MOS), 39
Medium access control (MAC)
layer, 132–34
Memorandum of understanding
(MoU), 316–17
Microcells, 198–99, 253, 326
capacity, 252
defined, 251
deployment strategies, 251
See also Cells
Microwave links, 201–2
Microwave multipoint distribution
system (MMDS), 141, 147
Microwave video distribution system
(MVDS), 141, 144–49
Military radio usage, 158
Minimum shift keying (MSK)
defined, 56
Gaussian (GMSK), 56, 59, 61
performance comparison, 59
Mission statement, 337
Mobile application part
(MAP), 174, 175
Mobile radio
basics, 19–82
cellular, 85–106
cordless, 127–35
private (PMR), 7, 107–25
public access (MR), 108, 110
satellite, 128, 149–54
video distribution, 128, 154–59
WLL, 128, 135–39
Mobile radio networks
accounting, 211–22
bill generation, 243
business care, 223–37
capacity enhancement, 246–53
configuration, changing, 241–42
customer care, 243–44
deployment, 205
designing, 191–209
economics of, 211–37
equipment manufacturers, 208–9
future, 269–77
interconnection, 199–203
large users of, 255–68
license application, 205–7
link budget, 195
monitoring, 240–44
operating, 239–53
operations and maintenance
(O&M), 203–4
planning, 193–96
for police, 265–66
progress in, 269–70
range comparison, 262
roll-out process, 192
statistics, 240–41
subscribers, adding/deleting, 242
supplier selection, 204–5
tariff policies, 244–45
technical design, 191–205
theoretical capacity of, 80–82
396 The Complete Wireless Communications Professional
Mobile radio operators, 290–94
auctions and, 291–94
number of, 296–97
Mobile station integrated services
digital network number
(MSISDN), 100–101
Mobile switching center (MSC), 47
gateway (GMSC), 90
paging messages and, 91
Mobile Telephone System (MTS), 8
Mobitex, 360
Modulation, 55–64
π/4DQPSK, 106, 123
amplitude (AM), 56–58, 62–63
classes, 56
frequency (FM), 56–58
idealized scheme, 59
phase (PM), 56, 58
quadrature, 61–63
waveforms, 57
Monitoring, 240–44
correct working of network, 242
fraud, 242–43
MPT1327, 117–19
channels, 118
control channel, 118
defined, 117
message types, 118–19
See also Private mobile radio
(PMR)
Multipath propagation
illustrated, 23
vectorial representation, 25
Multiple access, 68–78
CDMA, 14, 69, 72–78, 322–27
FDMA, 13, 68, 69–71
PRMA, 69
SDMA, 69
TDMA, 13, 14, 68, 71–72, 322–27
types of, 68–69
Multiple reuse patterns, 247, 253
Multipulse excited (MPE) codecs, 44
N
Net present value (NPV), 235
calculation example, 237
positive, 236
Network costs, 223–26
base station, 226
hardware, 225
spreadsheet example, 226
subscriber unit, 223–25
switching, 226
types of, 225
See also Mobile radio networks
Network integration
solutions, 181–82
advantages/disadvantages, 182
definition, 181–82
See also Fixed mobile
convergence (FMC)
Network operation, 239–53
capacity enhancement
and, 246–53
monitoring and, 240–44
tariffs and, 244–45
See also Mobile radio networks
Network overlay solutions, 180–81
advantages/disadvantages, 181
characteristics, 180–81
defined, 180
See also Fixed mobile
convergence (FMC)
Nordic Mobile Telephone 450
(NMT450), 9
Nortel system, 145
Nyquist theorem, 39
Index 397
O
Offset QPSK (O-QPSK), 64
One-way algorithms, 48
Operating expenses, 227
Operations and maintenance
(O&M), 203–4
Opportunities, 334
Orthogonal code families, 76–77
Orthogonal frequency division
multiplexing (OFDM), 157
P
Packet reservation multiple access
(PRMA), 69
Packet switching, 79–80, 165
disadvantages, 79
types of, 79–80
Paging
channels (PCHs), 102
GSM, 91–92
Papers, writing, 345–46
Parametric encoders, 40
Path loss, 21
PBR. See Private mobile radio (PMR)
PCM speech coding, 40
Personal digital cellular (PDC), 106
Personal handiphone system
(PHS), 134–35
capacity, 320
channel types, 135
defined, 134
delay, connection, power
consumption, 321
infrastructure cost, 320–21
interworking with GSM, 321
provision of 64-kbps bearers, 321
provision of repeaters, 321
simplicity of planning, 321
See also DECT vs. PHS
PEST (political, economic, social,
technical), 333
Phase modulation (PM)
defined, 56
illustrated, 58
See also Modulation
Picocells, 198–99
Planet, 197–98
Planning and strategic
management, 330
Pleiochronous digital hierarchy
(PDH), 171
Point-to-multipoint overlay
networks, 202–3
Police, 263–66
introduction to, 263–64
radio system selection, 265–66
requirements, 264–65
See also Large users
Political changes, 333
Post and Telecommunication
Organization (PTO), 9
Power control
accurate, 78
error sensitivity, 77
systems, 77–78
Presentations
giving, 342–43
preparing, 340–42
See also Conferences
Private finance initiative (PFI), 317
Private mobile radio
(PMR), 7, 107–25
cellular vs., 261–63
choice of, 111–14
CTCSS, 115–16
defined, 107
European, 110
growth, 111
introduction, 107–14
marketplace, 108–11
migration to cellular, 113–14
398 The Complete Wireless Communications Professional
MPT1327, 117–19
problems, 111
simple, 114–19
TETRA, 119–25
trunked, 117
user breakdown, 109
See also Mobile radio
Profit and loss account, 212–15
depreciation, 214–15
EBIT, 215
illustrated, 213–14
prediction, 212
See also Accounting
Propagation
multipath, 23
path loss, 21
principles of, 20–31
Protocols, 170–78
ATM, 176–78
CCITT7, 174–75
frame relay, 175–76
framing structure, 170–72
interexchange signaling, 172
ISDN, 173–74
R2 signaling system, 172–73
TCP/IP, 176
X25, 175
See also Fixed networks
Pseudorandom noise (PN)
codes, 77, 104
Public access mobile radio
(PAMR), 108
European market, 110
wireless professionals working
for, 256
Publications, 340–46
Public land mobile networks
(PLMNs), 231
Public safety radio communications
project (PSRCP), 317
Public-switched telephone network
(PSTN), 80, 90, 231
Pulse shaping, 59–61
PureVoice, 45
Q
Quadrature modulation, 61–63
amplitude (QAM), 62–63
See also Modulation
Quadrature PSK (QPSK)
π/4differential, 106, 123
constellation, 64
offset (O-QPSK), 64
phase lock, 67
Qualcomm, 14–15, 45, 87, 322
Qualifications, 349–50
MBA and, 349
Ph.D and, 349
Quantization error, 38
R
R2 signaling system, 172–73
defined, 172
multiple frequency version, 173
tone signaling in, 173
See also Protocols
Radio planning, 196–98
finances, 197
topography, 197
Radio spectrum, 281–97
Allocation/assignment
methods, 287–89
amount of, 32
auctions, 291–94
defined, 32
government policy, 294–97
GSM, efficiency, 101
management, 32, 282–87
mandated standards and, 356
Index 399
Radio spectrum (continued)
mobile radio operators
and, 290–94
pricing, 288
sufficient, 33
trading, 289
users, 154–59
utilization, 32–37
value, 289
Radio systems, 154–58
basic design of, 37–78
block diagram, 38
carrier recovery, 66–68
channel imperfections, 48–55
clock recovery, 64–66
digital, 37, 38, 155
error rates, 49, 50
frequency/phase
modulation, 55–64
multiple access, 68–78
overview, 37
secure transmission, 46–48
voice encoding, 37–46
See also Mobile radio networks
Railways, 257–63
communications within
Europe, 258–59
constraints, 261
controllers, 260
introduction to, 257–58
local communications, 260
PMR vs. cellular, 261–63
remote control and, 260
requirements, 259–61
See also Large users
Raised-cosine (RC) filters, 59–60
characteristic, 59
defined, 59
impulse response, 60
Rayleigh fading, 22–28
defined, 22–23
modeling, 25
received signal amplitude, 25
signal strength probability, 26
waveform, 26
Regular pulse excited (RPE)
codec, 44, 45
Request for quotations (RFQ), 204
Research
National/international,
programs, 348
organization links, 346–48
university, sponsorship of, 347–48
use of, 346–47
Research into Advanced
Communications in Europe
(RACE) program, 348
Revenue, 227–33
calculation overview, 229
classes, 228
spreadsheet example, 230
See also Business case
Roaming
CDMA, 326
European, 355
Root mean square (RMS), 39
S
Satellite systems, 149–54
concept, 150–53
defined, 128
Earth stations, 150, 152
economics, 153–54
geostationary, 150
introduction, 149–50
Iridium, 153
LEO, 151–52
links, 203
VSAT, 151, 203
See also Mobile radio
Sealed bid first price
auctions, 291–92
400 The Complete Wireless Communications Professional
Second-price sealed bid
auctions, 292
Secure transmission, 46–48
Selective calling (SELCALL), 116
Service control point (SCP), 167
Service switching point (SSP), 167
Shannon law, 80–81
Short-range business radio
(SRBR), 12
Signaling connection and control
part (SCCP), 167
Signal-to-interference ratio (SIR), 81
SIM toolkit, 273
Single frequency networks
(SFNs), 155, 158
Slotted-Aloha protocol, 121
Slow associated control channel
(SACCH), 94, 124
Slow fading, 21–22
SMR, 107
choice of, 111–14
defined, 107
digital services, 108
marketplace, 108
market predictions, 109
operators, 108
Social factors, 333
Space division multiple access
(SDMA), 69
Special mobile group
(SMG), 300–301
defined, 300
subgroups, 300–301
See also European
Telecommunications
Standardization Institute
(ETSI)
Specific cell channels (SCCHs), 135
Speech
AbS coder, 42
coders, 40
decoder, 41
framing format for, 93–94
modeling, 40
PCM codings, 40
sampling process, 39
unvoiced, 41, 42
voiced, 41, 42
waveform components, 39
Standards, 299–307
early adoption of, 357
enforced use of, 358
ETSI, 300–302, 304–5
introduction to, 299–300
mandating, 353–63
openness of, 356–57
stages, 304–5
Standards-making
bodies, 300–304
U.S., 302–4
writing, 304–7
Strategy
implementation, 330
inappropriate, 338
statement of, 337
See also Corporate strategy
Strengths, 333
Subscriber Identity Module
(SIM), 47
Subscribers
adding/deleting, 242
tariffs per, 245
unit costs, 223–25
Superframes, 97
Switches
design of, 162–65
lines between, 170
packet, 165
time-space-time, 163, 164
SWOT (strengths, weaknesses,
opportunities, threats), 334
Synchronization channel (SCH), 102
Synchronizer, 66
Index 401
Synchronous digital hierarchy
(SDH), 168, 171
Synchronous optical network
(SONET), 171
Synthesizer hopping, 249
T
Tadiran system, 145
Tariffs
per subscriber, 245
policies, 244–45
TCP/IP, 176
Technical developments, 333
Telecommunications Industry
Association (TIA)
accreditation, 303
divisions, 302
wireless communications
division, 303
Telecommunications management
network (TMN), 168–69
common management
information protocol
(CMIP), 169
defined, 168
managed objects (MOs), 169
Teledesic, 142
Telephones, number structure, 169
Telepoint, 13–14
Terrestrial trunked radio
(TETRA), 10, 11, 119–25,
263, 265, 286
ambient listening, 314
APCO25 and, 13
area coverage techniques, 124–25
back-to-back operation, 314
bandwidth requirement, 315
call reestablishment, 122
cellular channel reuse, 125
defined, 119
dynamic group allocation, 314
expense of, 318
extended mode, 123
framing structure, 123–24
functionality, 318
gain, 315
introduction to, 119–20
load apportionment, 314
minimum mode, 123
network design, 120
network overview, 120
normal mode, 122–23
packet data optimized (TETRA
PDO), 119
quasi-synchronous
transmission, 125
security, 121
shared, 316–17
single-site wide area
coverage, 124
specification, 13
spectrum efficiency, 318
system operation, 120–23
technical parameters, 123–25
technology evaluation, 313–15
time sharing
transmission, 123, 125
voice and data system
(TETRA V+D), 119
See also Private mobile radio
(PMR); TETRA vs. GSM
TETRA vs. GSM, 313–19
background, 313
debate analysis, 318–19
economic comparison, 315–18
technology evaluation, 313–15
Thermionic diode, 6
Third generation systems, 270–77
designing, 274–77
parties involved in, 270
requirements, 270–71
standardization, 15
402 The Complete Wireless Communications Professional
vision of, 270–74
Threats, 334
Time division multiple access
(TDMA), 13, 14, 106
cost, 326
defined, 68
expense comparison, 72
frequency planning, 325
guard bands, 71
inefficiency, 323–24
interference distribution, 324–25
problems, 71–72
range, 325
risk, 326
timing, 71
See also CDMA vs. TDMA;
Multiple access
Times-n carrier recovery, 67
Time-space-time switches, 163, 164
Times-two clock recovery, 66
Total Access Communications
System (TACS), 9
Traffic channels, 35
defined, 93
for half-rate coding, 96
PHS, 135
structure for full-rate coding, 95
See also Channels
Transaction capability application
part (TCAP), 167
Transistor, 7
Transmission
cdmaOne downlink, 102, 103
cdmaOne uplink, 103–4
circuit-switched, 79
packet, 79–80
quasi-synchronous, 125
secure, 46–48
time sharing, 125
within GSM, 93–101
Transmit power control, 247
Trellis diagram, 52, 53, 54
complete, 54
start of, 53
Trunking gain, 36
TV
digital, 155, 158
systems, 154–58
U
Underlay/overlay cells, 247
U.S. standardization, 302–4
Universal mobile
telecommunications service
(UMTS), 186, 273–74
air interface, 275
allocation, 286
University research
sponsorship, 347–48
User packet channels (UPCHs), 135
V
Value chain, 335–36
defined, 335
illustrated, 336
Very small aperture terminals
(VSATS), 151, 203
Video distribution
services, 141–42, 154–59
defined, 128
local multipoint (LMDS), 141
microwave (MVDS), 141
microwave multipoint
(MMDS), 141
types of, 141
Visitor’s location register (VLR), 88
Viterbi decoders, 50, 54, 55
Voice encoding, 37–46
Index 403
W
Walsh codes, 104
Weaknesses, 333
Wideband channels, 29–31
Winner’s curse, 294
Wireless local loop (WLL)
systems, 29, 135–49
access technologies, 137–42
advantages, 140
cellular vs., 142–43
constraints on, 144–45
copper infrastructure, 138–39
defined, 128
deployment, 136
ideal, 148
introduction, 135–37
Nortel, 145
products, 145–48
provisions, 144
Tadiran, 145
technologies, 144–49
comparison, 146
market segments, 149
progress, 148–49
strengths/weaknesses, 147
See also Mobile radio
Wireless office, 184–85
advantages/disadvantages, 185
definition, 184–85
See also Fixed mobile convergence
(FMC)
Writing standards, 304–7
X
X25 protocol, 175
Z
Zero-crossing clock recovery, 66
404 The Complete Wireless Communications Professional

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