Transmit Power on APs constantly changing

rhunter · ‎09-17-2007

I am having some complaints about users in one of our bulldings saying their connection is in/out. Looking into the logs/events on WLC, we see that the APs in that building are changing their transmit power once a minute and sometimes more.

Any ideas on what could be causing the transmit power to fluctuate constantly? Interference? rogue?

pmccubbin · ‎09-17-2007

Are any of the APs rebooting? We had a situation where an in-line power card which some of a building's APs were plugged into was of a pre 802.3af specification. The APs on this card consequently were constantly rebooting and the other APs were adjusting their power to compensate.

Interference could also be an issue. Are there any machines which could be causing RF interference?

Please report back and let the forum know what you discover.

Hope this helps.

rhunter · ‎09-17-2007

The APs are not rebooting.

So, if interference is an issue, what could it be? We are seeing some rogue access points in these buildings. Could they be causing the APs to change their power up and down. The APs are somewhat dense. There are 16 AP over 4 floors. The building is shaped like the letter "U".

dennischolmes · ‎09-19-2007

There are several possibilities based on what hardware you are using. If this solution is WLC based then you should not be seeing power shifts in single minute intervals. The system by default evaluates and makes adjustments every 10 minutes. See your RRM settings info in the configuration guide. Another issue could be placement of the APs on varying floors if using omnidirectional antennae. The APs should NEVER be place one on top of the other on adjacent floors. The fix, move the APs so that they are not directly on top of one another and use patch antennae to control the coverage areas. Another problem that has common symptoms to those you describe is an RF Phenomenon known as RF multipath distortion. In multipath distortion, the signal from an AP will bounce off of walls, floors, or metal obstructions creating an effect where the signal is split and arrives at the receiveing station at slightly different times. This is actually how 802.11n works but in your case you are using b/g. To fix this problem you will again need to evaluate your antennae. Make sure to use a diversity based antenna system as this is comprised of two separate antenna elements and will allow for the best signal received to be used. If all else fails, call in an RF expert.