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| Document Title | Microsoft Word - Canopy_System_Release_8_User_Guide,_Issue_2RegDraft.doc |
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| Document Author: | John Harris |
Release 8
Planning Guide
P LANNING G UIDE
Issue 2, December 2006
Draft for Regulatory Review
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Release 8
Planning Guide
12 ENGINEERING YOUR RF COMMUNICATIONS
Before diagramming network layouts, the wise course is to
◦
anticipate the correct amount of signal loss for your fade margin calculation
(as defined below).
◦
recognize all permanent and transient RF signals in the environment.
◦
identify obstructions to line of sight reception.
12.1 ANTICIPATING RF SIGNAL LOSS
The C/I (Carrier-to-Interference) ratio defines the strength of the intended signal relative
to the collective strength of all other signals. Canopy modules typically do not require a
C/I ratio greater than
12.1.1
◦
3 dB or less at 10-Mbps modulation and −65 dBm for 1X operation. The C/I ratio
that you achieve must be even greater as the received power approaches the
nominal sensitivity (−85 dBm for 1X operation).
◦
10 dB or less at 10-Mbps modulation and −65 dBm for 2X operation. The C/I ratio
that you achieve must be even greater as the received power approaches the
nominal sensitivity (−79 dBm for 2X operation).
◦
10 dB or less at 20-Mbps modulation.
Understanding Attenuation
An RF signal in space is attenuated by atmospheric and other effects as a function of the
distance from the initial transmission point. The further a reception point is placed from
the transmission point, the weaker is the received RF signal.
12.1.2
Calculating Free Space Path Loss
The attenuation that distance imposes on a signal is the free space path loss.
PathLossCalcPage.xls calculates free space path loss.
12.1.3
Calculating Rx Signal Level
The Rx sensitivity of each module is provided at
http://motorola.canopywireless.com/prod_specs.php. The determinants in Rx signal level
are illustrated in Figure 37.
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Tx antenna
gain
Rx antenna
gain
free space signal
Tx
cable
loss
Rx
cable
loss
distance
Rx
signal
level
Tx
power
receiver
or amplifier
Transmitter
transmitter
or Amplifier
amplifier
Figure 37: Determinants in Rx signal level
Rx signal level is calculated as follows:
Rx signal level dB = Tx power − Tx cable loss + Tx antenna gain
− free space path loss + Rx antenna gain − Rx cable loss
NOTE:
This Rx signal level calculation presumes that a clear line of sight is established
between the transmitter and receiver and that no objects encroach in the
Fresnel zone.
12.1.4
Calculating Fade Margin
Free space path loss is a major determinant in Rx (received) signal level. Rx signal level,
in turn, is a major factor in the system operating margin (fade margin), which is calculated
as follows:
system operating margin (fade margin) dB =Rx signal level dB − Rx sensitivity dB
Thus, fade margin is the difference between strength of the received signal and the
strength that the receiver requires for maintaining a reliable link. A higher fade margin is
characteristic of a more reliable link.
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12.2 ANALYZING THE RF ENVIRONMENT
An essential element in RF network planning is the analysis of spectrum usage and the
strength of the signals that occupy the spectrum you are planning to use. Regardless of
how you measure and log or chart the results you find (through the Spectrum Analyzer in
SM and BHS feature or by using a spectrum analyzer), you should do so
◦
at various times of day.
◦
on various days of the week.
◦
periodically into the future.
As new RF neighbors move in or consumer devices in your spectrum proliferate, this will
keep you aware of the dynamic possibilities for interference with your network.
12.2.1
Mapping RF Neighbor Frequencies
Canopy modules allow you to
◦
use an SM or BHS (or a BHM reset to a BHS), or an AP that is temporarily
transformed into an SM, as a spectrum analyzer.
◦
view a graphical display that shows power level in RSSI and dBm at 5-MHz
increments throughout the frequency band range, regardless of limited selections
in the Custom Radio Frequency Scan Selection List parameter of the SM.
◦
select an AP channel that minimizes interference from other RF equipment.
The SM measures only the spectrum of its manufacture. So if, for example, you wish to
analyze an area for both 2.4- and 5.7-GHz activity, take both a 2.4- and 5.7-GHz SM to
the area. To enable this functionality, perform the following steps:
CAUTION!
The following procedure causes the SM to drop any active RF link. If a link is
dropped when the spectrum analysis begins, the link can be re-established
when either a 15-minute interval has elapsed or the spectrum analyzer feature is
disabled.
Procedure 2: Analyzing the spectrum
1. Predetermine a power source and interface that will work for the SM or BHS in
the area you want to analyze.
2. Take the SM or BHS, power source, and interface device to the area.
3. Access the Tools web page of the SM or BHS.
RESULT: The Tools page opens to its Spectrum Analyzer tab. An example of this
tab is shown in Figure 143.
4. Click Enable.
RESULT: The feature is enabled.
5. Click Enable again.
RESULT: The system measures RSSI and dBm for each frequency in the
spectrum.
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6. Travel to another location in the area.
7. Click Enable again.
RESULT: The system provides a new measurement of RSSI and dBm for each
frequency in the spectrum.
NOTE: Spectrum analysis mode times out 15 minutes after the mode was
invoked.
8. Repeat Steps 6 and 7 until the area has been adequately scanned and logged.
=========================== end of procedure ======================
As with any other data that pertains to your business, a decision today to put the data into
a retrievable database may grow in value to you over time.
RECOMMENDATION:
Wherever you find the measured noise level is greater than the sensitivity of the
radio that you plan to deploy, use the noise level (rather than the link budget) for
your link feasibility calculations.
12.2.2
Anticipating Reflection of Radio Waves
In the signal path, any object that is larger than the wavelength of the signal can reflect
the signal. Such an object can even be the surface of the earth or of a river, bay, or lake.
The wavelength of the signal is approximately
◦
2 inches for 5.2- and 5.7-GHz signals.
◦
5 inches for 2.4-GHz signals.
◦
12 inches for 900-MHz signals.
A reflected signal can arrive at the antenna of the receiver later than the non-reflected
signal arrives. These two or more signals cause the condition known as multipath. When
multipath occurs, the reflected signal cancels part of the effect of the non-reflected signal
so, overall, attenuation beyond that caused by link distance occurs. This is problematic at
the margin of the link budget, where the standard operating margin (fade margin) may be
compromised.
12.2.3
Noting Possible Obstructions in the Fresnel Zone
The Fresnel (pronounced fre·NEL) Zone is a theoretical three-dimensional area around
the line of sight of an antenna transmission. Objects that penetrate this area can cause
the received strength of the transmitted signal to fade. Out-of-phase reflections and
absorption of the signal result in signal cancellation.
The foliage of trees and plants in the Fresnel Zone can cause signal loss. Seasonal
density, moisture content of the foliage, and other factors such as wind may change the
amount of loss. Plan to perform frequent and regular link tests if you must transmit
though foliage.
12.2.4
Radar Signature Detection and Shutdown
With Release 8.1, Canopy meets ETSI EN 301 893 v1.2.3 for Dynamic Frequency
Selection (DFS). DFS is a requirement in certain countries of the EU for systems like
Canopy to detect interference from other systems, notably radar systems, and to avoid
co-channel operation with these systems. All 5.4 GHz modules and all 5.7 GHz
Connectorized modules running Release 8.1 have DFS. Other modules running Release
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8.1 do not. With Release 8.1, Canopy SMs and BHSs as well as Canopy APs and BHMs
will detect radar systems.
When an AP or BHM enabled for DFS boots, it receives for 1 minute, watching for the
radar signature, without transmitting. If no radar pulse is detected during this minute, the
module then proceeds to normal beacon transmit mode. If it does detect radar, it waits for
30 minutes without transmitting, then watches the 1 minute, and will wait again if it
detects radar. If while in operation, the AP or BHM detects the radar signature, it will
cease transmitting for 30 minutes and then begin the 1 minute watch routine. Since an
SM or BHS only transmits if it is receiving beacon from an AP or BHM, the SMs in the
sector or BHS are also not transmitting when the AP or BHM is not transmitting.
When an SM or BHS with DFS boots, it scans to see if an AP or BHM is present (if it can
detect a Canopy beacon). If an AP or BHM is found, the SM or BHS receives on that
frequency for 1 minute to see if the radar signature is present. For an SM, if no radar
pulse is detected during this 1 minute, the SM proceeds through normal steps to register
to an AP. For a BHS, if no radar pulse is detected during this 1 minute, it registers, and
as part of registering and ranging watches for the radar signature for another 1 minute. If
the SM or BH does detect radar, it locks out that frequency for 30 minutes and continues
scanning other frequencies in its scan list.
Note, after an SM or BHS has seen a radar signature on a frequency and locked out that
frequency, it may connect to a different AP or BHM, if color codes, transmitting
frequencies, and scanned frequencies support that connection.
For all modules, the module displays its DFS state on its General Status page. You can
read the DFS status of the radio in the General Status tab of the Home page as one of
the following:
◦
Normal Transmit
◦
Radar Detected Stop Transmitting for n minutes, where n counts
down from 30 to 1.
◦
Checking Channel Availability Remaining time n seconds, where
n counts down from 60 to 1. This indicates that a 30-minute shutdown has
expired and the one-minute re-scan that follows is in progress.
DFS can be enabled or disabled on a module’s Radio page: Configuration > Radio >
DFS.
Operators in countries with regulatory requirements for DFS must not disable the feature
and must ensure it is enabled after a module is reset to factory defaults.
Operators in countries without regulatory requirements for DFS will most likely not want
to use the feature, as it adds no value if not required, and adds an additional 1 minute to
the connection process for APs, BHMs, and SMs, and 2 minutess for BHSs.
−
RECOMMENDATION:
Where regulations require that radar sensing and radio shutdown is enabled, you
can most effectively share the spectrum with satellite services if you perform
spectrum analysis and select channels that are distributed evenly across the
frequency band range.
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A connectorized 5.7-GHz module provides an Antenna Gain parameter. When you
indicate the gain of your antenna in this field, the algorithm calculates the appropriate
sensitivity to radar signals, and this reduces the occurrence of false positives (wherever
the antenna gain is less than the maximum).
12.3 USING JITTER TO CHECK RECEIVED SIGNAL QUALITY
The General Status tab in the Home page of the Canopy SM and BHS displays current
values for Jitter. This is an index of overall received signal quality. Interpret the jitter
value as indicated in Table 32.
Table 32: Signal quality levels indicated by jitter
Correlation of Highest Seen
Jitter to Signal Quality
Signal
Modulation
High
Quality
Questionable
Quality
Poor
Quality
1X operation
(2-level FSK)
0 to 4
5 to 14
15
2X operation
(4-level FSK)
0 to 9
10 to 14
15
In your lab, an SM whose jitter value is constant at 14 may have an incoming packet
efficiency of 100%. However, a deployed SM whose jitter value is 14 is likely to have
even higher jitter values as interfering signals fluctuate in strength over time. So, do not
consider 14 to be acceptable. Avoiding a jitter value of 15 should be the highest priority in
establishing a link. At 15, jitter causes fragments to be dropped and link efficiency to
suffer.
Canopy modules calculate jitter based on both interference and the modulation scheme.
For this reason, values on the low end of the jitter range that are significantly higher in 2X
operation can still be indications of a high quality signal. For example, where the amount
of interference remains constant, an SM with a jitter value of 3 in 1X operation can
display a jitter value of 7 when enabled for 2X operation.
However, on the high end of the jitter range, do not consider the higher values in 2X
operation to be acceptable. This is because 2X operation is much more susceptible to
problems from interference than is 1X. For example, where the amount of interference
remains constant, an SM with a jitter value of 6 in 1X operation can display a jitter value
of 14 when enabled for 2X operation. As indicated in Table 32, these values are
unacceptable.
12.4 USING LINK EFFICIENCY TO CHECK RECEIVED SIGNAL QUALITY
A link test, available in the Link Capacity Test tab of the Tools web page in an AP or BH,
provides a more reliable indication of received signal quality, particularly if you launch
tests of varying duration. However, a link test interrupts traffic and consumes system
capacity, so do not routinely launch link tests across your networks.
12.4.1
Comparing Efficiency in 1X Operation to Efficiency in 2X Operation
Efficiency of at least 98 to 100% indicates a high quality signal. Check the signal quality
numerous times, at various times of day and on various days of the week (as you
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checked the RF environment a variety of times by spectrum analysis before placing
radios in the area). Efficiency less than 90% in 1X operation or less than 60% in 2X
operation indicates a link with problems that require action.
12.4.2
When to Switch from 2X to 1X Operation Based on 60% Link Efficiency
In the above latter case (60% in 2X operation), the link experiences worse latency (from
packet resends) than it would in 1X operation, but still greater capacity, if the link remains
stable at 60% Efficiency. Downlink Efficiency and Uplink Efficiency are measurements
produced by running a link test from either the SM or the AP. Examples of what action
should be taken based on Efficiency in 2X operation are provided in Table 33.
Table 33: Recommended courses of action based on Efficiency in 2X operation
Module Types
Advantage AP
with
Advantage SM
Further Investigation
Result
Recommended Action
Check the General Status tab
of the Advantage SM. See
Checking the Status of 2X
Operation on Page 93.
Uplink and
downlink are both
≥60% Efficiency.
Rerun link tests.
Rerun link tests.
Uplink and
downlink are both
≥60% Efficiency.
Optionally, re-aim SM, add a
reflector, or otherwise mitigate
interference. In any case, continue
2X operation up and down.
Check the General Status tab
of the Canopy SM. See
Checking the Status of 2X
Operation on Page 93.
Uplink and
downlink are both
≥60% Efficiency.
Rerun link tests.
Uplink and
downlink are both
≥60% Efficiency.
Optionally, re-aim SM, add a
reflector, or otherwise mitigate
interference. In any case, continue
2X operation up and down.
Results are
inconsistent and
range from 20% to
80% Efficiency.
Monitor the Session Status tab in
the Advantage AP.
Monitor the Session Status tab
in the Advantage AP.
Link fluctuates
between 2X and
1X operation.
Optionally, re-aim SM, add a
reflector, or otherwise mitigate
interference. Then rerun link tests.
Rerun link tests.
No substantial
improvement with
consistency is
seen.
On the General tab of the SM,
disable 2X operation. Then rerun
link tests.
Rerun link tests.
Uplink and
downlink are both
≥90% Efficiency.
Continue 1X operation up and
down.
Rerun link tests.
Advantage AP
with
Canopy SM
NOTES:
1.
Or check Session Status page of the Advantage AP, where a sum of greater than 7,000,000 bps for the
up- and downlink indicates 2X operation up and down (for 2.4- or 5.x-GHz modules.
2.
For throughput to the SM, this is equivalent to 120% Efficiency in 1X operation, with less capacity used at
the AP.
This link is problematic.
3.
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12.5 CONSIDERING FREQUENCY BAND ALTERNATIVES
For 5.2-, 5.4-, and 5.7-GHz modules, 20-MHz wide channels are centered every 5 MHz.
For 2.4-GHz modules, 20-MHz wide channels are centered every 2.5 MHz. This allows
the operator to customize the channel layout for interoperability where other Canopy
equipment is collocated.
Cross-band deployment of APs and BH is the recommended alternative (for example,
a 5.2-GHz AP collocated with 5.7-GHz BH).
IMPORTANT!
Regardless of whether 2.4-, 5.2-, 5.4-, or 5.7-GHz modules are deployed,
channel separation between modules should be at least 20 MHz for 1X operation
or 25 MHz for 2X.
12.5.1
900-MHz Channels
900-MHz Single AP Available Channels
A single 900-MHz AP can operate with the 8-MHz wide channel centered on any of the
following frequencies:
906
907
908
(All Frequencies in MHz)
909 912 915 918 922
910 913 916 919 923
911 914 917 920 924
900-MHz AP Cluster Recommended Channels
Three non-overlapping channels are recommended for use in a 900-MHz AP cluster:
(All Frequencies in MHz)
906
915
924
This recommendation allows 9 MHz of separation between channel centers. You can use
the Spectrum Analysis feature in an SM, or use a standalone spectrum analyzer, to
evaluate the RF environment. In any case, ensure that the 8-MHz wide channels you
select do not overlap.
12.5.2
2.4-GHz Channels
2.4-GHz BH and Single AP Available Channels
A BH or a single 2.4-GHz AP can operate in the following channels, which are separated
by only 2.5-MHz increments.
(All Frequencies in GHz)
2.4150 2.4275 2.4400 2.4525
2.4175 2.4300 2.4425 2.4550
2.4200 2.4325 2.4450 2.4575
2.4225 2.4350 2.4475
2.4250 2.4375 2.4500
The channels of adjacent 2.4-GHz APs should be separated by at least 20 MHz.
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IMPORTANT!
In the 2.4-GHz frequency band, an SM can register to an AP that transmits on a
frequency 2.5 MHz higher than the frequency that the SM receiver locks when
the scan terminates as successful. This establishes a poor-quality link. To
prevent this, select frequencies that are at least 5 MHz apart.
2.4-GHz AP Cluster Recommended Channels
Three non-overlapping channels are recommended for use in a 2.4-GHz AP cluster:
(All Frequencies in GHz)
2.4150 2.4350 2.4575
This recommendation allows 20 MHz of separation between one pair of channels and
22.5 MHz between the other pair. You can use the Spectrum Analysis feature in an SM
or BHS, or use a standalone spectrum analyzer, to evaluate the RF environment. Where
spectrum analysis identifies risk of interference for any of these channels, you can
compromise this recommendation as follows:
◦
Select 2.4375 GHz for the middle channel
◦
Select 2.455 GHz for the top channel
◦
Select 2.4175 GHz for the bottom channel
In any case, ensure that your plan allows at least 20 MHz of separation between
channels.
12.5.3
5.2-GHz Channels
Channel selections for the AP in the 5.2-GHz frequency band range depend on whether
the AP is deployed in cluster.
5.2-GHz BH and Single AP Available Channels
A BH or a single 5.2-GHz AP can operate in the following channels, which are separated
by 5-MHz increments.
(All Frequencies in GHz)
5.275
5.280
5.285
5.290
5.295
5.300
5.305
5.310
5.315
5.320
5.325
The channels of adjacent APs should be separated by at least 20 MHz. However,
25 MHz of separation is advised.
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5.2-GHz AP Cluster Recommended Channels
Three non-overlapping channels are recommended for use in a 5.2-GHz AP cluster:
(All Frequencies in GHz)
5.275
5.300
5.325
12.5.4
5.4-GHz Channels
Channel selections for the AP in the 5.4-GHz frequency band range depend on whether
the AP is deployed in cluster.
5.4-GHz BH and Single AP Available
A BH or single 5.4-GHz AP can operate in the following channels, which are separated
by 5-MHz.
5495
5500
5505
5510
5515
5520
5525
5530
5535
5540
5545
5550
5555
5560
5565
5570
(All Frequencies in GHz)
5575 5595 5615
5580 5600 5620
5585 5605 5625
5590 5610 5630
5635
5640
5645
5650
5655
5660
5665
5670
5675
5680
5685
5690
5695
5700
5705
The channels of adjacent APs should be separated by at least 20 MHz.
5.4-GHz AP Cluster Recommended Channels
The fully populated cluster requires only three channels, each reused by the module that
is mounted 180° opposed. In this frequency band range, the possible sets of three nonoverlapping channels are numerous. As many as 11 non-overlapping 20-MHz wide
channels are available for 1X operation. Fewer 25-MHz wide channels are available for
1X operation, where this greater separation is recommended for interference avoidance.
5.4-GHz AP Cluster Limit Case
In the limit, the 11 channels could support all of the following, vertically stacked on the
same mast:
◦
3 full clusters, each cluster using 3 channels
◦
a set of 4 APs, the set using the 2 channels that no AP in any of the 3 full
clusters is using
IMPORTANT!
Where regulations require you to have Dynamic Frequency Selection (DFS)
enabled, analyze the spectrum, then spread your channel selections as evenly
as possible throughout this frequency band range, appropriately sharing it with
satellite services.
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12.5.5
Planning Guide
5.7-GHz Channels
Channel selections for the AP in the 5.7-GHz frequency band range depend on whether
the AP is deployed in cluster.
5.7-GHz BH and Single AP Available ISM/U-NII Channels
A BH or a single 5.7-GHz AP enabled for ISM/U-NII frequencies can operate in the
following channels, which are separated by 5-MHz increments.
(All Frequencies in GHz)
5.735 5.765 5.795 5.825
5.740 5.770 5.800 5.830
5.745 5.775 5.805 5.835
5.750 5.780 5.810 5.840
5.755 5.785 5.815
5.760 5.790 5.820
The channels of adjacent APs should be separated by at least 20 MHz. However,
25 MHz of separation is advised.
5.7-GHz AP Cluster Recommended ISM/U-NII Channels
Six non-overlapping ISM/U-NII channels are recommended for use in a 5.7-GHz AP
cluster:
(All Frequencies in GHz)
5.735
5.775
5.815
5.755
5.795
5.835
The fully populated cluster requires only three channels, each reused by the module that
is mounted 180° offset. The six channels above are also used for backhaul point-to-point
links.
As noted above, a 5.7-GHz AP enabled for ISM/U-NII frequencies can operate on a
frequency as high as 5.840 GHz. Where engineering plans allow, this frequency can be
used to provide an additional 5-MHz separation between AP and BH channels.
12.5.6
Channels Available for OFDM Backhaul Modules
Channel selections for BHs in the OFDM series are quoted in the user guides that are
dedicated to those products. However, these BHs dynamically change channels when
the signal substantially degrades. Since the available channels are in the 5.4- and
5.7-GHz frequency band ranges, carefully consider the potential effects of deploying
these products into an environment where traffic in this range pre-exists.
12.5.7
Example Channel Plans for AP Clusters
Examples for assignment of frequency channels and sector IDs are provided in the
following tables. Each frequency is reused on the sector that is at a 180° offset. The entry
in the Symbol column of each table refers to the layout in Figure 38 on Page 142.
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NOTE:
The operator specifies the sector ID for the module as described under Sector
ID on Page 439.
Table 34: Example 900-MHz channel assignment by sector
Direction of Access
Point Sector
Frequency
Sector ID
Symbol
North (0°)
906 MHz
Northeast (60°)
915 MHz
Southeast (120°)
924 MHz
South (180°)
906 MHz
Southwest (240°)
915 MHz
Northwest (300°)
924 MHz
Table 35: Example 2.4-GHz channel assignment by sector
Direction of Access
Point Sector
Frequency
Sector ID
Symbol
North (0°)
2.4150 GHz
Northeast (60°)
2.4350 GHz
Southeast (120°)
2.4575 GHz
South (180°)
2.4150 GHz
Southwest (240°)
2.4350 GHz
Northwest (300°)
2.4575 GHz
Table 36: Example 5.2-GHz channel assignment by sector
140
Direction of Access
Point Sector
Frequency
North (0°)
Sector ID
Symbol
5.275 GHz
Northeast (60°)
5.300 GHz
Southeast (120°)
5.325 GHz
South (180°)
5.275 GHz
Southwest (240°)
5.300 GHz
Northwest (300°)
5.325 GHz
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Table 37: Example 5.4-GHz channel assignment by sector
Direction of Access
Point Sector
Frequency
North (0°)
Sector ID
Symbol
5.580 GHz
Northeast (60°)
5.620 GHz
Southeast (120°)
5.660 GHz
South (180°)
5.580 GHz
Southwest (240°)
5.620 GHz
Northwest (300°)
5.660 GHz
Table 38: Example 5.7-GHz channel assignment by sector
12.5.8
Direction of Access
Point Sector
Frequency
North (0°)
Sector ID
Symbol
5.735 GHz
Northeast (60°)
5.755 GHz
Southeast (120°)
5.775 GHz
South (180°)
5.735 GHz
Southwest (240°)
5.755 GHz
Northwest (300°)
5.775 GHz
Multiple Access Points Clusters
When deploying multiple AP clusters in a dense area, consider aligning the clusters as
shown in Figure 38. However, this is only a recommendation. An installation may dictate
a different pattern of channel assignments.
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Figure 38: Example layout of 7 Access Point clusters
12.6 SELECTING SITES FOR NETWORK ELEMENTS
The Canopy APs must be positioned
142
◦
with hardware that the wind and ambient vibrations cannot flex or move.
◦
where a tower or rooftop is available or can be erected.
◦
where a grounding system is available.
◦
with lightning arrestors to transport lightning strikes away from equipment.
◦
at a proper height:
−
higher than the tallest points of objects immediately around them (such as
trees, buildings, and tower legs).
−
at least 2 feet (0.6 meters) below the tallest point on the tower, pole, or roof
(for lightning protection).
◦
away from high-RF energy sites (such as AM or FM stations, high-powered
antennas, and live AM radio towers).
◦
in line-of-sight paths
−
to the SMs and BH.
−
that will not be obstructed by trees as they grow or structures that are later
built.
Draft for Regulatory Review
Issue 2, December 2006
Release 8
Planning Guide
NOTE:
Visual line of sight does not guarantee radio line of sight.
12.6.1
Resources for Maps and Topographic Images
Mapping software is available from sources such as the following:
◦
http://www.microsoft.com/streets/default.asp
−
◦
Microsoft Streets & Trips (with Pocket Streets)
http://www.delorme.com/software.htm
−
DeLorme Street Atlas USA
−
DeLorme Street Atlas USA Plus
−
DeLorme Street Atlas Handheld
Topographic maps are available from sources such as the following:
◦
◦
http://www.delorme.com/software.htm
−
DeLorme Topo USA
−
DeLorme 3-D TopoQuads
http://www.usgstopomaps.com
−
Timely Discount Topos, Inc. authorized maps
Topographic maps with waypoints are available from sources such as the following:
◦
http://www.topografix.com
−
TopoGrafix EasyGPS
−
TopoGrafix Panterra
−
TopoGrafix ExpertGPS
Topographic images are available from sources such as the following:
◦
http://www.keyhole.com/body.php?h=products&t=keyholePro
−
◦
http://www.digitalglobe.com
−
12.6.2
keyhole PRO
various imagery
Surveying Sites
Factors to survey at potential sites include
◦
what pre-existing wireless equipment exists at the site. (Perform spectrum
analysis.)
◦
whether available mounting positions exist near the lowest elevation that satisfies
line of site, coverage, and other link criteria.
◦
whether you will always have the right to decide who climbs the tower to install
and maintain your equipment, and whether that person or company can climb at
any hour of any day.
Issue 2, December 2006
Draft for Regulatory Review
143
Planning Guide
12.6.3
Release 8
◦
whether you will have collaborative rights and veto power to prevent interference
to your equipment from wireless equipment that is installed at the site in the
future.
◦
whether a pre-existing grounding system (path to Protective Earth ) exists, and
what is required to establish a path to it.
◦
who is permitted to run any indoor lengths of cable.
Assuring the Essentials
In the 2.4-, 5.2-, 5.4-, and 5.7-GHz frequency band ranges, an unobstructed line of sight
(LOS) must exist and be maintainable between the radios that are involved in each link.
Line of Sight (LOS) Link
In these ranges, a line of sight link is both
◦
an unobstructed straight line from radio to radio.
◦
an unobstructed zone surrounding that straight line.
Fresnel Zone Clearance
An unobstructed line of sight is important, but is not the only determinant of adequate
placement. Even where the path has a clear line of sight, obstructions such as terrain,
vegetation, metal roofs, or cars may penetrate the Fresnel zone and cause signal loss.
Figure 39 illustrates an ideal Fresnel zone.
Fresnel zone
receiver
transmitter
Transmitter
or Amplifier
Figure 39: Fresnel zone
FresnelZoneCalcPage.xls calculates the Fresnel zone clearance that is required between
the visual line of sight and the top of an obstruction that would protrude into the link path.
Non-Line of Sight (NLOS) Link
The Canopy 900-MHz modules have a line of sight (LOS) range of 40 miles (more than
64 km) and greater non-line of sight (NLOS) range than Canopy modules of other
frequency bands. NLOS range depends on RF considerations such as foliage,
topography, obstructions.
12.6.4
Finding the Expected Coverage Area
The transmitted beam in the vertical dimension covers more area beyond than in front of
the beam center. BeamwidthRadiiCalcPage.xls calculates the radii of the beam coverage
area.
144
Draft for Regulatory Review
Issue 2, December 2006
Release 8
12.6.5
Planning Guide
Clearing the Radio Horizon
Because the surface of the earth is curved, higher module elevations are required for
greater link distances. This effect can be critical to link connectivity in link spans that are
greater than 8 miles (12 km). AntennaElevationCalcPage.xls calculates the minimum
antenna elevation for these cases, presuming no landscape elevation difference from one
end of the link to the other.
12.6.6
Calculating the Aim Angles
The appropriate angle of AP downward tilt is derived from both the distance between
transmitter and receiver and the difference in their elevations. DowntiltCalcPage.xls
calculates this angle.
The proper angle of tilt can be calculated as a factor of both the difference in elevation
and the distance that the link spans. Even in this case, a plumb line and a protractor can
be helpful to ensure the proper tilt. This tilt is typically minimal.
The number of degrees to offset (from vertical) the mounting hardware leg of the support
tube is equal to the angle of elevation from the lower module to the higher module (
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