Rayleigh Fading Channels *

Abstract

This chapter addresses Rayleigh fading, which affects mobile systems such as cellular and personal communication systems. It explains the fundamental fading manifestations, types of degradation, and methods to mitigate the degradation. The chapter examines two particular mitigation techniques: the Viterbi equalizer implemented in the Global System for Mobile Communication, and the Rake receiver used in Code Division Multiple Access systems built to meet Interim Standard-95. When the mechanisms of fading channels were first modeled in the 1950s and 1960s, the ideas were primarily applied to over-the-horizon communications covering a wide range of frequency bands. Small-scale fading is also called Rayleigh fading because if the multiple reflective paths are large in number and there is no line-of-sight signal component, the envelope of the received signal is statistically described by a Rayleigh pdf. In the case of Rayleigh fading, parameters with overbars are often introduced to indicate that a mean is being taken over the "ups" and "downs" of the fading experience.