User guide

Canopy System User Guide Using the Frame Calculator Tool (All) for
Co-location
pmp-0229 (Mar 2013)
543
The second step to avoid interference is to configure parameters on all APs of the same frequency
band in proximity such that they have compatible transmit/receive ratios (all stop transmitting
each frame before any start receiving). This avoids the problem of one AP attempting to receive
the signal from a distant SM while a nearby AP transmits, which could overpower that signal.
The following parameters on the AP determine the transmit/receive ratio:
• Max Range
• Downlink Data percentage
• (reserved) Control Slots
If all the APs of a given frequency band are FSK APs or all are OFDM APs, the simplest way to
avoid interference is to set these three parameters with identical values on all APs in proximity. If
OFDM and FSK APs of the same frequency band are in proximity, or if you want APs set to
different parameters (differing in their Max Range values, for example), then you should use the
Frame Calculator to identify compatible settings.
The frame calculator is available on the Frame Calculator tab of the Tools web page. To use the
Frame Calculator, type into the calculator various configurable parameter values for each proximal
AP, and then record the resulting Uplink Rcv SQ Start value. Next vary the Downlink Data
percentage in each calculation and iterate until the calculated Uplink Rcv SQ Start for all co-
located APs are within 300 bit times; if possible, within 150 bit times. In Cambium Point-to-
Multipoint systems, 10 bit times = 1 µs.
OFDM modules provide an OFDM Frame Calculator and FSK modules provide an FSK Frame
Calculator. To perform frame calculations for co-located OFDM and FSK modules, you must use
an OFDM module for the OFDM calculations and an FSK module for the FSK calculations.
The calculator does not use values in the module or populate its parameters. It is merely a
convenience application that runs on a module. For this reason, you can use any FSK module (AP,
SM, BHM, BHS) to perform FSK frame calculations for setting the parameters on an FSK AP and
any OFDM module (AP, SM, BHM, BHS) to perform OFDM frame calculations for setting the
parameters on an OFDM AP.
IMPORTANT!
APs that have slightly mismatched transmit-to-receive ratios and low levels of
data traffic may see little effect on throughput. A system that was not tuned for
co-location may work fine at low traffic levels, but encounter problems at higher
traffic levels. The conservative practice is to tune for co-location before traffic
ultimately increases. This prevents problems that occur as sectors are built.
An example of the Frame Calculator tab is shown in Figure 184.