In communications, the additive white Gaussian noise (AWGN) channel is one in which the only impairment is the linear addition of wideband Gaussian noise with a constant spectral density (expressed as watts per hertz of bandwidth). There is no fading, frequency selectivity, interference, nonlinearity or dispersion.

Wideband Gaussian noise comes from many natural sources, such as the thermal vibrations of atoms in antennas, "black body" radiation from the earth and other warm objects, and from celestial sources such as the sun.

The AWGN channel is a good model for many satellite and deep space communication links. It is not a good model for most terrestrial links because of multipath, terrain blocking, interference, etc.