Chapter 3 - The Mobile Channel and Diversity Reception in CDMA Systems

Abstract

The chapter focuses on the mobile channel and diversity reception in code division multiple access (CDMA) systems. Mobile wireless transmissions undergo more distortion in the mobile channel than do wireline systems. These effects result in distortion of the transmitted signal and are a result of several factors, including reflectors in the transmission path, mobile velocity, the transmission frequency (that is, carrier frequency), and other parties' attempts to utilize the transmission band. Generally, the signal to be transmitted is shaped as a pulse to restrict its bandwidth. Receivers are also designed using bandpass filters to isolate the signal of interest. As a result, the effects of the mobile channel are usually considered only in the band of interest, as effects outside the transmission band are assumed to be suppressed through receiver filtering. The chapter also describes the mobile radio channel in wireless systems and introduces concepts, such as multipath, coherence bandwidth, fading, and diversity, along with an overview of the power control mechanism in CDMA systems in relation to interference issues specific to CDMA systems. Also included is an introduction to some of the fundamental aspects of accurate reception of a CDMA signal, the diversity reception through the use of a rake receiver, and the application of feedback power control to CDMA systems to combat the near-far effect.