Please could someone take a look at this:
Quoting the manual:
"The system uses Time Division Duplexing (TDD) - one channel alternately
transmits and receives - rather than using one channel for transmitting
and a second channel for receiving. To accomplish TDD, the AP must provide sync to its SMs – it must keep them in sync. Furthermore, collocated APs must be synced together - an unsynchronized AP that transmits during the receive cycle of a collocated AP can prevent that second AP from being able to decode the signals from its SMs."
If we think of 2 collocated APs that use different non-overlapping
channels in the same band, say 5.735 for AP-A and 5.775 for AP-B, how
would AP-A “prevent the second AP from being able to decode signals from its SMs”, even if they were unsynchronized, considering that it operates on a totally different channel?
If it is true that each AP uses ONLY its configured non-overlapping
frequency channel, there would be no way for one AP to interfere with the
other, even if their transmit/receive cycle was not synchronized.
In other words, if APs that are APPARENTLY on different, non-overlapping channels, but within the same band, must be “synchronized” in order to co-exist well, this is implying APs are actually transmitting or at least working in some way with the whole band.
Isn’t this comparable to saying, from Canopy’s perspective: “I will use the whole band I was built for, no matter what channel you configured me at, if you want to co-exist with me, synchronize, if not, be aware that I use ALL your channels”.
We are not trying to put it into a commercial perspective (i.e. Canopy vs others), but really can’t find a precise technical answer. Any opinion/suggestion will be appreciated.
Thanks,
Diego Cosalter.-
The reason this happens is because RF bands aren’t sharply defined chunks with edges in the real world. There is a slight curve to the frequencies in use that causes some overlap. As well, the receivers pick up everything on all channels, but only try to decode the channel they’re working on. This means that everything else just turns into noise. A way around this is to install high quality band-pass filters on everything, but you may still run in to performance issues. They are intended as a last measure in a very RF noisy environment.
But this is somewhat different from your subject line - the problem with Canopy and WiFi on the same frequencies is that Canopy transmits all the time no matter how much data is being moved. Analogous to an old-school telephone “circuit” system instead of traffic only when there is data like on WiFi. Of course this exacerbates the noise issue since it never really goes away.
I think that APs could coexist even if not unsynchronized, but there must be some distance (e.g. few meters) and frequencies have to be as far as possible each other. Of course this could be a potential source of problems.
I have all of my AP (about 10) connected with 802.11 backhauls hosted on the same pole or tower (1 AP and 1 backhaul).
I always choose a frequency difference of at least 60 Mhz (on 5.4 band) and never had any particular interference/issue.