Cambium Networks PTP 450 Series, Configuration Manual

Page: 241 / 649

Chapter 1: Configuration Configuring radio parameters
Page
1-213
Example
Let us assume that all APs in a cluster have the same Max range settings, a 2.5 ms frame length and a 20
MHz channel BW, but the operator has fine-tuned the DL duty % per AP as follows:
AP1:
Max range: 2 miles
Contention slots: 3
DL duty cycle = 75%
AP2:
Max range: 2 miles
Contention slots: 3
DL duty cycle = 80%
Running the frame calculator as explained in the Steps for co-location , the AP1 Antenna Transmit End
and Antenna Receive start times are:
• AP1 Antenna Transmit End = 1.6440 ms
• AP1 Antenna Receive Start = 1.7972 ms
AP2’s Antenna Transmit End and Antenna Receive start times are:
• AP2 Antenna Transmit End = 1.7411 ms
• AP2 Antenna Receive Start = 1.8943 ms
The settings in AP1 in the cluster are now modified by changing the number of contention slots from 3
to 7, for example because this sector is constantly experiencing a higher volume of VoIP traffic.
Running the frame calculator again, the new AP1 Antenna Transmit End and Antenna Receive start times
are:
• AP1 Antenna Transmit End = 1.5711 ms
• AP1 Antenna Receive Start = 1.7243 ms
The two equations above have to be checked for correct co-location:
• AP1 Antenna Receive Start > AP2 Antenna Transmit End

1.7243 ms >1.7411 ms NOT OK
• AP2 Antenna Receive Start > AP1 Antenna Transmit End

1.8943 ms >1.5711ms OK
The first of the two equations are not true. AP2 is still transmitting when AP1 has already started
receiving. This creates interference at the AP1 receiver.
To avoid this interference scenario, the duty cycle of AP2 can be further adjusted slightly. For example,
changing the duty cycle of AP2 from 80% to 79% changes the AP2 Antenna Transmit End and Antenna
Receive start times as follows:
• AP2 Antenna Transmit End = 1.7168 ms
• AP2 Antenna Receive Start = 1.8700 ms
The two equations have to be checked again for co-location:
• AP1 Antenna Receive Start > AP2 Transmit End

1.7243 ms >1.7168 ms OK
• AP2 Receive Start > AP1 Transmit End

1.8700 ms >1.5711 ms OK
Now both equations are true and the APs can be co-located.