Advances in Multiuser Detection

5

GENERIC MULTIUSER DETECTION AND STATISTICAL PHYSICS

Dongning Guo and Toshiyuki Tanaka

5.1 INTRODUCTION

Fuelled by the advent and rapid development of cellular telephony, the problem of multiuser signal detection (or separation) has received great attention since the mid-1980s as one of the major avenues towards optimal error performance and spectrum usage in wireless communications. This chapter introduces the concept of generic multiuser detection and summarizes some recent advances in the analysis and design of generic detectors using statistical physics techniques.

5.1.1 Generic Multiuser Detection

Consider a multidimensional communication system in which each user randomly generates a “signature vector” and modulates its own (usually error-control coded) symbols onto the signature for transmission. The received signal is the superposition of all users' signals corrupted by Gaussian noise. With knowledge of all signature vectors, the goal of a multiuser receiver is to reliably recover the information intended for all or a subset of the users. The multiuser channel, best described by a vector model, is very versatile and is widely used in applications that include code-division multiple access (CDMA) as well as certain multiple-input multiple-output (MIMO) systems.

The maximum information rate through a multiuser channel is achieved by jointly optimal decoding, which is prohibitively complex for all but a small user population and codeword length. Hence, the tasks of untangling ...