ACS seems not to select the best channel in 2.4GHz.

Eduard GV eduardgv at
Fri Feb 6 05:14:16 EST 2015

>> What I'd like to try (at some point, when I have time and resources)
>> is a different formula for the interference_factor. Something like the
>> linear sum of the average signal level measured in all channels
>> (applying attenuation factors) and weighted by their utilization.
> I'd certainly welcome experimentation in this area.

Does anyone have half a dozen or so compatible devices to spare :D ?

>> Why not 1, 5, 9, 13 (where available)?
> That is somewhat of a complex area..


> It would actually be interesting to see some statistics on operating
> channel use in European deployments. Some quick searches through public
> reports on this seemed to point towards channels 1, 6, 11 being used in
> around 75% cases and 5, 9, 13 having a minimal (< 10 % in total) use.

We conducted a survey in Barcelona and found it was ~60% for the
triumvirate (i.e. 1, 6, 11), and ~40% for the rest of the 2.4GHz
channels (~15% of the total in the set 5, 9, 13). We gathered more
interesting data which we will hopefully publish soon.

> In addition to the actual deployments, there are station implementation
> reasons for 1, 6, 11 being a convenient set. Number of scan
> optimizations make it more likely for APs to be found on those channels,
> e.g., due to them being searched first or more frequently and channel 13
> being scanned only with passive scanning. In addition, some P2P use
> cases are quite a bit more efficient if the AP connection is on one of
> the social channels (which, surprise surprise, are those 1, 6, 11).

One final insight in this regard... we were allowed to "play" with the
Wi-Fi infrastructure of a small campus to test our centralized channel
management algorithm with their ~100 APs. Those APs coexisted with
other ~100 "rogue" APs. In the beginning, most of the ~200 APs were on
either 1, 6 or 11. After two weeks managing our ~100 APs' channels
(using the whole available spectrum), the "rogue" APs (the channel
selection mechanism of which is unknown to us) reacted so that,
eventually, the channel distribution became fairer (> 50% of them in
the set 1, 5, 9, 13).

> All that said, it may make sense to provide an option for configuring
> different bias for which channels to prefer. There may be reasons that
> give different preferences even between whatever the set of selected
> common channels are, so making this a bit more flexible could be useful.


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