In
wireless communications,
fading is deviation of the
attenuation affecting a signal over certain propagation media. The fading may vary with time, geographical position or radio frequency, and is often modeled as a
random process. A
fading channel is a communication channel that experiences fading. In wireless systems, fading may either be due to
multipath propagation, referred to as
multipath induced fading, or due to shadowing from obstacles affecting the
wave propagation, sometimes referred to as
shadow fading.