Error Correction Coding, 2nd Edition

Chapter 19Fading Channels and Space‐Time Codes

19.1 Introduction

For most of this book the codes have been designed for transmission through either an AWGN channel or a BSC. One exception is the convolutive channel, for which turbo equalization was introduced in Section 14.7. In this chapter, we introduce a coding technique appropriate for Rayleigh flat fading channels. Fading is a multiplicative change in the amplitude of the received signal. As will be shown in Section 19.2, fading is mitigated by means of diversity, that is, multiple, independent transmissions of the signal. Space‐time coding provides a way of achieving diversity for multiple transmit antenna systems with low‐complexity detection algorithms.

A very important “meta‐lesson” from this chapter is that the coding employed in communicating over a channel should match the particular requirements of the channel. In this case, space‐time codes are a response to the question: Since diversity is important to communicating over a fading channel, how can coding be used to obtain diversity for portable receivers?

A discussion of the fading channel and its statistical model are presented in Section 19.2. In Section 19.3, the importance of diversity in combating fading is presented. Section 19.4 presents space‐time codes, which are able to provide diversity with only a single receive antenna and moderate decode complexity. Trellis codes used as space‐time codes are presented in Section 19.5.

19.2 Fading Channels

In the ...