Networking / Beginners

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Spectrum management services

Spectrum management services are a special subset of station services. They are designed to allow the wireless network to react to conditions and change radio settings dynamically. Two services were defined in 802.11h to help meet regulatory requirements.

The first service, transmit power control (TPC), can dynamically adjust the transmission power of a station. Access points will be able to use the TPC operations to advertise the maximum permissible power, and reject associations from clients that do not comply with the local radio regulations. Clients can use TPC to adjust power so that range is "just right" to get to the access point. Digital cellular systems have a simliar feature designed to extend the battery life of mobile phones. Lower transmit power also will have some benefit in the form of increased battery life, though the extent of the improvement will depend on how much the transmit power can be reduced from what the client would otherwise have used.

Power control also helps to simplify the electronics in the base station because all signals will be received at roughly the same signal.

The second service, dynamic frequency selection (DFS), was developed mainly to avoid interfering with some 5 GHz radar systems in use in Europe. Although originally developed to satisfy European regulators, the underlying principles have been required by other regulators as well. DFS was key to the U.S. decision to open up more spectrum in the 5 GHz band in 2004. DFS includes a way for the access point to quiet the channel so that it can search for radar without interference, but the most significant part of DFS is the way that it can reassign the channel on an access point on the fly. Clients are informed of the new channel just before the channel is switched.