Report: Packet communications on a mobile radio channel

The cellular mobile phones first developed by AT&T Bell Laboratories operate in the 800- to 900-MHz band. A property of this mobile radio channel is that the FM signal undergoes multipath fading because of scattering and reflections from buildings and obstructions.^1,2,3 As a result, the amplitude of the signal received at any point over distances of a few hundred wavelengths is not constant but varies randomly about a mean level with a Rayleigh distribution while its phase is uniformly distributed between 0 and 2π. When the instantaneous value falls substantially below that mean, a fade is said to occur and noise captures the receiver. If a voice signal is being transmitted, the received speech is interrupted with noise bursts that appear in the form of pops and clicks that may persist even under idle channel conditions. If digital data is being transmitted over the FM channel, these fades cause error bursts in the received data. (The use of the same RF channel in an adjacent cell causes co-channel interference. This interfering signal is also Rayleigh-distributed but is independent of the desired channel and leads to similar noise bursts.)