Minimum channel seperation

Products ePMP
1

Whats the minimum channel seperation between sectors in GPS TDD mode?

2

5Mhz

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3

Can someone post an example of channels?
What exactly do you mean by saying “channel separation”?

4

Well, good RF guidlines will tell you to have twice the channel separation of your channel size.  So, with regular WiFi gear, if you're using 20 Mhz wide channels, you'd want to have at least 40 Mhz of channel separation between them (a 'guard zone') so that you don't self interfere. However, with Cambium's GPS sync, you can have as little as a 5Mhz guard zone and have the same benefits.

So, for example, if you're using 2.4 Ghz and 20 Mhz wide channel, and if you select channel 1 (2412Mhz) that is actually transmitting from 2402 to 2422 because it's 20 Mhz wide and 'centered' on 2412.  So, without GPS sync, you'd normally have to have 40 Mhz between the top of your channel use (2422 + 40Mhz) and so the bottom of the next channel would be 2462 - which means you'd have to use 2472 as center, so that transmit on 2462-2482...   and that's a problem obviously because there isn't really room to do that in the allowable frequencies.

Of course, in 5Ghz, there IS actually more room to accomplish that, and of course many choose to use only 10 Mhz wide channels in 2.4Ghz (and therefor only need a 20 Mhz guard zone) in order to be able to fit more frequencies together and so on.  BUT, the point is to have 'separation' between the top of one channel that you're using and the bottom of the next channel you're using.


NOW - with GPS Sync and proper network design, because all the AP's can be synced to transmit at the same time, and to all switch to receive at the same time, you really only need a 5Mhz wide guard zone to have the same effect. So, using my example above, if one radio is on 2412 (2402-2422) then the next radio could be on 2437 (2427-2447) and a third could be on 2462 (2452-2472) and between all three of these, there is 5Mhz of unused 'guard zone', and with a properly synced system (Cambium GPS) that's all that's needed.  MUCH, MUCH more spectrally efficient.

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5

Great explanation! Thank you ninedd!

6

Thank you. The support guys say you need 40mhz but it cant be.

7
@mono2 wrote:

Thank you. The support guys say you need 40mhz but it cant be.

That may be the case if you're not using sync and/or you're using non-OEM antennas that have poor F/B ratios.

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