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Srini Grahadurai

high b/g channel utilization

Hi guys, having lot of issues after adding 8 extra AP's in our warehouse floor to get more coverage. Out of the existing 32 AP's on the floor 70% of the AP's have more than 80% channel utilization. It is b/g network so we use 1,6,11. We dont use TPC or DCA as we had lot of issues in our warehouse with it before. The transmit power is custom "1". Data rates 1 and 2 are set to mandatory..will disabling it help? I am going with the spectrum analyzer tommorow to see if i can find something. We have VoWLAN (used sparringly though) in the same 2.4Ghz spectrum too will it increase the duty cycles? I have scaled down the QoS from platinum to best-effort but its still the same. Bounced couple of AP's but no luck. I think it is co-channel interference but utilization over 80% and in some AP's it is  even 91% ....quite ridiculous.    

Any suggestions are appreciated!



Hi Srini,

It's tough to tell you what changes to make without seeing your current run-config so we can see the total RF snapshot of your environment.  The spectrum analyzer look mostly like BT, but maybe some DECT phones as well since you mentioned.  Several topics above are quite valid regarding channel utilization but be sure to consider the specific requirements of the clients you are servicing before making changes relative to their communication.

I'm not sure what version you were running the last time you used the WLCs RRM features, but this is really probably your best bet, but may require some tweaking.  With those 8.5dbi antennas maxed at power level one, you may be overpowering your environment, but I can't say for sure without run-config.

I would usually suggest the WLC's RRM defaults a starting baseline.  I'm not sure what version your last RRM experience was with, but this is quite a polished solution.  You may need to make various changes, but you can get a better understanding of the current RF based upon the WLC's choices. 

For instance, if you set all RRM to Defalut and Auto and after several intervals you find your power levels dropping to 4, 5, and so on, you would immediately know that your manual power assignment is severely impacting the RF with co-channel interference.  Given your description, I wouldn't suspect your power levels would stay at levels 1 and 2, but can't say for sure without current run-config.

The TAC says it is layer 1 inteference as I found from airmagnet spectrum. May be the environment is too hot as well as we use custom power level for all AP's as 1. Now that we have increased AP density i am thinking whether TPC can help to reduce co-channel interference as we can play with only 1,6 and 11. Proper site-survey wasn't done as we followed the standard AP placement template for warehouse.

The AP is wall mounted 8m high from the floor with no tilt of antennas. The aisles are fully stocked and 7m high it looks like a thick we are just skeptical about the coverage we would received in the middle of the floor especially from 1-3m from the floor.

I think TPC is based upon the readings received from neighbors.In our environment most of the AP's can see each other so TPC will decrease the power of the AP but the client will get bad signal especially in the middle of the floor.

Studying the signal pattern of the antenna we use it helps to have a tilt towards the floor by an there any formula to calculate the tilt in a indoor environment? To start with we are going to disable 1M and try to find the interference source.

Thanks guys.

TPC could certianly help out.  If you have added even more APs and are still maxing power at one, you are probably pretty hot.  TPC will make the "best" choice in regards to power levels.   Please also consider the maximum transmit power of your clients.  Maxing the AP out to reach your center aisle could have zero effect (and mostly negative) if your clients have a max 50mw transmit power; just as an example.  the AP needs to hear your client, so I wouldn't depend on your client having "more bars" as indication of proper performance for that client.  The interference appears to be BT due to the FHSS CU sequencing, which is a concern, but the power level assignments could be doing more harm than these.

Without a site survey it's anybody's guess what's best for your environment.  Again, a run-config would go a long ways in making suggestions for you.

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