They should hear one another and coordinate, if I remember correctly. And this is indeed better than the situation where a router or access point is transmitting across a range that straddles another range of frequencies. In the 2.4GHz band, transmitting devices do not use one ‘channel number’ but a whole range of frequencies, so that for example channels 1 and 6 do not overlap but any closer than that, say 1 and 5 or 2 and 6 and there will be some corruption.
If the channels are only spaced four apart, eg 1 and 5, any degradation from frequency overlap will be extremely extremely mild and in that case basically harmless, but 1 and 4 would not be good.
In fact, the only channel numbers that should ever be used are 1 6 and 11+ or alternatively 1 5 9 13 provided that both (i) all four are actually being used and (ii) all neighbours also agree to use that arrangement and not a mixture of 1 5 9 13 plus 1 6 11. If a network is so heavily loaded that it is better to have four always busy channels than three, then the 33% extra capacity that is made available is worth the very slight performance degradation that comes from spacing of 4 channels apart rather than 5.
If your neighbours are using 2, 3, 4, 5, 7, 8, 9, 10 then have them killed, with the one exception of the case where you are all willing to agree to the 1 5 9 13 plan instead of 1 6 11. You will also have to be careful to watch out for the arrival of any new neighbours who do not know that you are using 1 5 9 13 and who will wreck everything by using the standard 1 6 11 layout.
In 2.4GHz transmitting a standard 20MHz wide channel occupies just one of the three slots 1 6 11. Occasionally some greedy people get double speed performance by transmitting on a double-width channel, 40MHz wide and so occupying both say 1+6 or 6+11. This is not a good idea if you have neighbours as there are then only two valid slots. If you are miles from anywhere then it’s different of course.
In 5GHz, there is none of this overlapping channel numbers nonsense and with a standard 20MHz wide channel you can’t transmit on the wrong channel numbers so straddling someone else. The 5GHz channel numbers are multiples of 5MHz and the only possible numbers are multiples of 4 ( 4 * 5MHz = 20MHz) eg 36 40 44 48 etc. I’m not sure whether it is even possible to use weird numbers such as 37,48,39.
Transmitting on a pair of adjacent channels is common, such as channel 36 + 40 (which occupies 36-39 40-43 if you like). It is important not to get out of step with neighbours with this though, so that your pairs half-overlap one another, so do not have one person transmitting on 36+40 and the other on 40+44. Agree on a common pattern of 5GHz channel use if you are going to use 40MHz wide channels (pairs).
In 5GHz more recent kit can use even more than just two channels ie 40MHz wide. 80MHz (four adjacent channels) and even 160MHz (eight adjacent channels) is sometimes possible. Using these can clearly be a disaster unless coordinated with neighbours.
The only 80MHz wide groupings that I would allow would be sets of fours as follows:
36-48 (ie 36+40+44+48)
52-64
100-112
116-128
124-136
149-161
So it is possible to get into a real mess with using the wrong blocks of multiple 5GHz channel numbers when using extra-wide channels.
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Topic: Routers broadcasting WiFi on the same channel number (Read 1616 times)