PMP 400 and PTP 200 Series
Canopy User Guide Supplement
Issue 3, January 2009
Page 15 of 45
•
Showing relative power levels across the band, to aid in selecting channels and
performing RF planning.
•
Troubleshooting to finding the frequency, relative power level, and location of
interferers by rotating a single SM, or triangulating from multiple SMs in a
geographical area.
The OFDM spectrum analyzer, the FSK spectrum analyzer, and the FSK
Receive Power Level
are all measuring and displaying
peak
power levels. The OFDM
Receive
Power
Level
is
measuring and displaying the
average
power level. In addition, an OFDM SM measures power
across 10-MHz channels while an FSK SM measures power across 20-MHz channels.
Due to all this, the reported
Receive
Power
Level
on an OFDM SM can be 10 to 15 dB lower
than the value shown for that channel on the spectrum analyzer. For example, for an OFDM AP
transmitting on 5540 MHz, the OFDM SM might show a
Receive
Power
Level
of -70 dBm while
the OFDM and FSK spectrum analyzers show power levels of -54 and -51 dBm at 5540 MHz.
The built-in spectrum analyzer can be very useful as a tool for troubleshooting and RF planning,
but doesn’t duplicate the accuracy and programmability of a dedicated, high-end spectrum
analyzer, which may be needed in some cases.
3.6
COLLOCATION OF 5.4 GHZ OFDM WITH STANDARD 5.4 GHZ
CANOPY FSK
When locating 5.4 GHz PMP 400 and PTP 200 Series OFDM APs near 5.4 GHz standard
Canopy FSK APs (especially on the same tower, but also in the same geographical area), the
following practices should be followed to avoid interference between the two systems:
•
Plan spacing between OFDM and FSK channels to provide
25 MHz center spacing
,
which gives a 10 MHz guard band between the 10 MHz OFDM channel and the 20
MHz FSK channel.
•
Coordinate
Downlink Data %, Range, and Control Slot settings using both the
OFDM and the FSK
frame calculators
The following paragraphs give more details on these recommended practices.
3.6.1
Channel Spacing
Center spacing of 25 MHz between collocated FSK and OFDM APs provides a 10 MHz guard
band between the 20 MHz and 10 MHz channels, which has proven useful and needed in field
testing. Alternatively, in cases where channel planning is severely restricted and the 10 MHz
guard band (25 MHz spacing) is not possible, using vertical separation of 5 feet or more between
the OFDM and FSK APs may allow collocation with no guard band (15 MHz spacing) in some
deployments.
3.6.2
Frame Calculations and Configuration Settings
Interference between collocated Canopy systems can be avoided by following two practices:
1. Use a CMM. This synchronizes frame start, so that all collocated APs begin
transmitting at the same time each 2.5 millisecond frame.
2. Use the frame calculators in each module, OFDM and FSK (the frame calculators are
different, as frame details are different) to select Downlink Data %, Range, and
Control Slots for each system that produce “Rec SEQ Start” values that are within
300 bit times. This ensures that all collocated APs end transmission each frame
before any collocated AP begins to receive.
