Disproportionate quantity of APs using channel 36

[aeccles]

We recently expanded our AP count from around 150 to 320 due to a building expansion.  After looking at some survey results, I saw a good deal of channel contention issues.  Surprisingly, 115 of my APs are using channel 36 while no other channels are used by more than 30 APs.  I confirmed all 9 of the standard channels (Non-DFS) are available in DCA, confirmed DCA was set to automatic, EDRRM is enabled, DCA channel sensitivity is set to medium. I invoked a channel update, but that didn't do much.  I just set it back to auto and set my interval to 8 hours instead of 24.  

I can see how there would be a default channel each AP starts with, then changes from when it sees the need to change.  36 makes sense.  BUT, I'm seeing APs in dense locations that are all sitting on 36.  In one instance, there are 6 aps in a room and 5 of those 6 are on ch36.  These APs are no more than 15 feet from each other and their power levels are all either 1 or 2. The next closest APs are at least 100 ft away.  My spectrum analyzer isn't picking up any interference in this area that would make the other channels off limits.  It doesn't make sense to to me that these haven't changed to another channel.

Can anyone explain this behavior?  A bug? I'm running an older version of code (8.3.150.0) because I have a few older APs I'm still in the process of replacing and need to stay on this version until that work is complete.

Thanks

[Jason Tyler]

Any reason why you have TPCv2 selected?

I suspect this is why most of your AP's will be at TX power level 1 or 2
Typically, TPCv1 is recommended (previously TPCv2 was only advised under TAC guidance)

I would suggest moving to TPCv1 and initialise your DCA, then monitor channel spread and tx power levels to see if they settle down

[aeccles]

It's been on TPCv1 forever, I actually just changed it to TPCv2 yesterday in an effort just try an get the AP channels to move.  I'll switch it back.

In my response to Scott, I noted that I do not have RF profiles set on the WLAN.  Could that be causing it?

[Jason Tyler]

Scott / Leo have give some good comments above.

if you have walked around with Ekahau and it's complaining that there's lots of interference, this could be due to the fact that the majority of the AP's are on pwr level 1 and could indeed be Co-channel interference.

I assume install has been implemented to best practice (survey for capacity / 5GHz / good cell overlap/survey for data& voice / between -67 to -65dB at the cell edge etc etc ) - if this is the case, then in theory, your access points should not be at max tx power
if the are, then revert back to TPCv1, initialise your DCA, let the system settle down on power levels and channels then evaluate

With regards to RF Profiles, you would have to evaluate these and what works best in that environment - these give you the ability to turn off datarates, TPC, CHDM etc, so again, unless you have configured these for specific reasons, in most cases the default may be good enough. So you would have to see if setting / changing these improves in your environment.