User's Manual

PMP 400/430 and PTP 200 Series Canopy User Guide
Supplement
Issue 4 0 – DRAFT 6 November 2009 Page 30 of 64
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 5.8 GHZ OFDM WITH STANDARD 5.7 GHZ
CANOPY FSK
When locating 5.8 GHz PMP 430 OFDM APs near 5.7 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.
When collocating only Canopy OFDM APs together, or collocating only Canopy hardware-
scheduled FSK APs together, the simple practice of setting the Downlink Data %, Range, and
Control Slots the same on all APs ensures they won’t interfere with each other. (These
parameters are set on the “Configuration => Radio” page of the AP.) However, due to the
different “physical” layer between Canopy OFDM and Canopy FSK, this doesn’t necessarily work
when collocating OFDM and FSK together.
You will need to use frame calculators on both the OFDM and FSK modules, as they are different
frame calculators. For the same Downlink Data %, Range, and Control Slots, the frame
calculators give different results. Use of the frame calculators is similar to the previous use when
collocating software-scheduled and hardware-scheduled APs.