Wireless channel

Wireless local area network channels using IEEE 802.11 protocols are sold mostly under the trademark WiFi.

The 802.11 workgroup has documented use in five distinct frequency ranges: 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, and 5.9 GHz bands. Each range is divided into a multitude of channels. Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges.

Fourteen channels are designated in the 2.4 GHz range, spaced 5 MHz apart from each other except for a 12 MHz space before channel 14.

For 802.11g/n, it is not possible to guarantee orthogonal frequency-division multiplexing (OFDM) operation, thus affecting the number of possible non-overlapping channels depending on radio operation.

As the protocol requires 16.25 to 22 MHz of channel separation (as shown above), adjacent channels overlap and will interfere with each other. Leaving three or four channels clear between used channels is recommended to avoid interference. The exact spacing required depends on the protocol and data rate selected as well as the electromagnetic environment where the equipment is used.

When two or more 802.11b transmitters are operated in the same airspace, their signals must be attenuated by -50 dBr and/or separated by 22 MHz to prevent interference. This is because the DSSS algorithm transmits data logarithmically along a 20 MHz bandwidth. The remaining 2 MHz gap is used as a guard band to allow sufficient attenuation along the edge channels.

Note: The 40 MHz bands in the diagram above are labelled with their centre channel numbers, but the management interface of many Wi-Fi devices labels one of these bands with the centre channel of one of the 20 MHz bands it overlaps plus an Up or Down notation to specify the other half of the band. For example, channel 3 in the diagram is called channel 1+Upper or Channel 5+Lower, and Channel 11 in the diagram is called Channel 9+Upper or Channel 13+Lower.

Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges. Network operators should consult their local authorities as these regulations may be out of date as they are subject to change at any time. Most of the world will allow the first thirteen channels in the spectrum.

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Wikipedia