I was asked last week about planning for coverage hole detection in a wireless network. The gentleman said he had a really good survey (design) and the guys that did the design really did a great job with their Air Magnet software and the heat maps proved it.
His problem wasn't the overlap of cells, co-channel interference, or anything like that... His main problem was that the survey was performed at the max power level of his VoIP devices (802.11 wireless phones). In doing so, in the event a coverage hole issue was triggered, the controller was turning the nearby access points up 3dB higher than the max power of the VoIP phones and issues were arising because of it.
The solution is to really go back and re-survey at a lower power level so that when a coverage hole detection is triggered and the controller has to turn the power up on a couple of access points, the power level will not be raised above the max power of the VoIP phones.
In his case, since the installation was complete and the moving of the access points was going to be really costly, we set his VoIP phones to the "G only" setting and allowed lower data rates on the network (Nothing 11MBs and below).
The spectrum analysis showed a clean environment for 2.4GHz and the phones were the only devices using the 2.4GHz band so it worked out great and he had no more issues with his phones.
Another lesson to remember when starting a new design (survey). Always know the devices you are going to have on your wireless network before designing it, and survey at power levels below the max power level of the weakest device you are going to deploy. This prepares you for a coverage hole detection without compromising the integrity of your wireless network.
Brett Hill, CWNE #147
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