adjacentchannel

An adjacent channel is a radio channel whose center frequency lies immediately next to another channel within a given spectrum allocation. In practical systems, channels have finite bandwidth, so their spectra extend beyond their nominal center frequency. When two channels are placed next to each other, the tail of one signal can spill into the adjacent channel, potentially causing interference unless adequate filtering and spectral separation are used. The term is commonly used in telecommunications, broadcasting, and wireless networking to describe the proximity of channels in a shared spectrum.

Adjacent-channel interference (ACI) arises from spectral leakage of transmitters, imperfect receiver selectivity, non-ideal filters, harmonics, and intermodulation products. Receiver front ends with insufficient selectivity or poor image rejection can misinterpret sidelobes from a neighboring channel as part of the desired signal, reducing signal quality and data rates. In dense deployments, strong signals on one channel can overwhelm nearby channels, especially when guard bands are small or equipment has a wide adjacent-band response.

To minimize ACI, regulators specify spectral masks and minimum channel spacing, and network designers insert guard bands between channels. Equipment manufacturers design transmitters and receivers with filters that sharply attenuate adjacent channels and measure performance with metrics such as adjacent-channel leakage ratio (ACLR). In wireless LANs and cellular networks, operators choose non-overlapping or minimally overlapping channels when possible; in 2.4 GHz Wi‑Fi, for example, channels 1, 6, and 11 are widely used to avoid overlap; in 5 GHz bands, many non-overlapping channels exist and radar-detection (DFS) can influence channel choice.

See also: adjacent-channel interference, channel spacing, spectral mask, guard band, ACLR, filter design.