Wireless Communications

7Diversity Techniques

Abstract

The error probability of coherent communication systems in AWGN drops exponentially with increased signal-to-noise ratio, , in accordance with the -function . When operating in a random field, multipath fading randomizes , thereby considerably degrading the average error performance. Indeed, a random field has a mechanism to damage the transmission reliability. Yet, there must be another mechanism therein for its solution. A possible remedy is to acquire multiple copies of the transmitted signal to smoothen its randomness. This can be done, for example, by placing a number of antennas over the random field. Such multiple copies can be combined in different ways, resulting in various diversity combining techniques, such as maximum ratio combining, equal-gain combining, selection combining, and post-detection combining. In this chapter, the reader is exposed to various diversity techniques and related mathematical skills used thereto.

7.1 Introduction

For the motivation of diversity techniques, let us examine the influence of multipath fading on transmission ...