Sometimes Less is More

In a world of universal mobile connectivity, the Wifi Internet provider is faced with serving population densities far exceeding those of the past.  Many of these  venues serve large groups of open, public or wireless guest access clustered in areas such as airport terminals, subways, train terminals, stadiums, hotels and other populated venues.  With so many users grouped so closely together, the potential for co-channel or adjacent channel interference is dramatically increased.

With multimedia emerging as the primary content of interest, controlling such interference becomes a major factor in maximizing available Wifi channel capacity to meet the traffic’s required bandwidth and latency demands.  Key factors for managing interference are the ability to control Access Point (AP) and client power levels.  While AP power has been managed and controlled effectively for quite some time now, the client’s power is set manually and not negotiated with the AP as is common between cell phones and their associated base stations.

For most clients, their Wifi’s power level is set by the device’s operating system software drivers to maximum, then forgotten.  When the Client’s radiation, be it on-channel or on an adjacent channel, reaches another AP to which it is not associated, it can cause interference to that AP’s channel, degrading its throughput.  In many cases where the Wifi infrastructure has been deployed casually without regard to power or channel management, the interference is so poor that it shuts the AP down.  Clients physically close to each other on the same channel but associated with different AP’s can also interfere with themselves and create channel contention to one another.

There is good news on the horizon for the Wifi Internet provider. The Wifi Working Group for 802.11k has developed what are called “Cooperative Control” mechanisms between the AP and its associated 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 summary 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 AP’s 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 to report the link quality it is seeing.

Once integrated into the Wifi Internet provider’s infrastructure and the Client’s operating system’s Wifi device drivers, these controls will go a long way to minimizing or preventing interference that can reduce or cripple channel capacity.  To learn more about the power of “Cooperative Control”, check out the 802.11 webpage:  http://www.ieee802.org/11/

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