The 802.11h specification is an addition to the 802.11 family of standards for wireless local area networks (WLANs). 802.11h is intended to resolve interference issues introduced by the use of 802.11a in some locations, particularly with military radar systems and medical devices.
The rules for 802.11h were recommended by the International Telecommunication Union (ITU) because of problems that arose with interference to and from other devices, especially in Europe. Two schemes are used to minimize interference. Dynamic frequency selection (DFS) detects the presence of other devices on a channel and automatically switches the network to another channel if and when such signals are detected. Transmit power control (TPC) reduces the radio-frequency (RF) output power of each network transmitter to a level that minimizes the risk of interference to and from other systems, while still allowing satisfactory network performance.