5.7 GHz Frequency Selection theory
Hi All,
I am setting up a 5.7 GHz system across the pond. We have access to all ismu-nii channels, 5735 – 5840 GHz. In the SM users manual (issue 5 page 61) Canopy suggests “AP’s should be separated by at least 20 MHz, however, 25 MHz of separation is advised”. Canopy also suggest only using 3 of the 6 channels, etc. I assume they want to reserve the other 3 channels for Backhaul units?
Since I am an Amateur Radio guy, I am well aware of the problems associated with “adjacent channel interference”. I am trying to understand how and why the AP’s get interference, and the only theory I can come up with, is if the SM’s they are listening for are very close in distance? A local SM transmitting 20 MHz away, could “de-sense a.k.a. Interference” with the AP on the next 20 MHz channel. There may be other issues too such as the AP’s TX/RX turn-on times (I need more info to understand).
Anyway, I came up with a frequency plan for 5.7 that I have implement in my system. Since I only have a few customers at this time, I have not been able to evaluate the system performance. I do not have any Backhauls on 5.7. Therefore I can use all six (20 Mhz) 5.7 GHz channels for AP antennas. I will be expanding to 6 towers total. This plan meets or exceeded all frequency separations recommended by Canopy and then some. And it seem to make expanding the cell structure better, with less potential for interference. I am open to any suggestions and comments.
Miles@telecron.com
This chart shows the Frequency, the Spacing between Adjacent channels and the frequency difference between channels on opposite sides of the tower. Assumes a 6 section system on 5.7 GHz.
Freq Ch Down Ch Up Ch Rear
A 5,735 60 40 20
B 5,775 40 40 20
C 5,815 40 60 25
D 5,755 60 85 40
E 5,840 85 45 65
F 5,795 45 60 20
Hi Miles,
Using the 3 channels is only when you have AP’s back to back. So one AP facing due north would have the same frequency as the other facing due south. The other 3 channels not used are not assumed to be reserved for backhauls as we highly recommend AP’s and BH’s being on separate bands. Example AP’s on 5.7 and BH’s on 5.2.
If you want to use all 6 channels then just make sure they are all non-overlapping as you did.
There is a decent white paper in our library that discusses interference. It can be found at http://motorola.canopywireless.com/libr … r91602.pdf
If the SM that is in close proximity is using the same frequency and is registered to the AP then there will be no interference. The AP and SM would be synchronized so that they transmit and receive at separate times. We use the CMM to provide a GPS clock source to keep the environment in sync.