Tuesday, October 26, 2010

More Power Means Less

While assembling some notes from a recent working group meeting, i was reminded of a discussion regarding Wi-Fi client power management; or lack thereof.  This is a major factor in maximizing available capacity for Multimedia-Grade environments given the density and close proximity of APs in such deployments. The problem, simply stated, is that a Wi-Fi client's RF power is set manually, not negotiated with the AP as is common to cell phones and their base stations.  For many clients, I've seen this power level set to max most of the time.  When the client's radiation, be it on-channel or adjacent channel, reaches another AP to which it is not associated, it can cause interference to that APs channel, degrading its throughput.  I've seen cases where in a "non-optimized" environment, the interference is so bad, it shuts the AP down.  

Fortunately help is on the way.  The Working Group for 802.11k is developing what are called "Cooperative Control" mechanisms between the AP and the client.  These are direct and positively acknowledged conversations that among other things, will allow the AP and client to negotiate power levels to optimize performance while minimizing interference.  Here is a mummery of relevant 802.11k features:
  • Beacon Report - The client reports Beacons that it detects to the AP.  This gives the AP and its associated controller more information about the environment seen by the client.
  • Neighbor Report - The AP sends a list of neighbor APs to the client.  This is used to reduce scanning.
  • Power Constraint Element - The AP instructs the client device to change (typically reduce) its transmit power.
  • Link Measurement Request/Report - The AP can ask the client o report the link quality it is seeing.

To learn more about the power of "Cooperative Control",  check out the 802.11 webpage:

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