Digital Communication Systems

CHAPTER

9

Signaling over Fading Channels

9.1    Introduction

In Chapters 7 and 8 we studied signaling over AWGN and band-limited channels, respectively. In this chapter we go on to study a more complicated communications environment, namely a fading channel, which is at the very core of ever-expanding wireless communications. Fading refers to the fact that even though the distance separating a mobile receiver from the transmitter is essentially constant, a relatively small movement of the receiver away from the transmitter could result in a significant change in the received power. The physical phenomenon responsible for fading is multipath, which means that the transmitted signal reaches the mobile receiver via multiple paths with varying spatio-temporal characteristics, hence the challenging nature of the wireless channel for reliable communication.

This chapter consists of three related parts:

First we study signaling over a fading channel by characterizing its statistical behavior in temporal as well as spacial terms. This statistical characterization is carried out from three different perspectives: physical, mathematical, and computational, each of which enriches our understanding of the multipath phenomenon in its own way. This first part of the chapter finishes with:

• BER comparison of different modulation schemes for AWGN and Rayleigh fading channels.
• Graphical display of how different fading channels compare to a corresponding AWGN channel using binary PSK.

This evaluation ...