Simplified Robust Adaptive Detection and Beamforming for Wireless Communications

7Robust Adaptive Beamforming

7.1 Introduction

The use of antenna arrays in a communication system can theoretically improve performance in terms of capacity and coverage [1–3]. In particular, a multi‐element antenna receiver at the base station of a cellular communication system is able to compensate for signal degradations in the mobile‐to‐base link caused by co‐channel interference. This is known to be the most important factor limiting the number of users that a system can handle [4]. Adaptive interference suppression techniques based on multi‐user detection and antenna array beamforming have recently been considered as a powerful method for increasing the quality, capacity and coverage of cellular systems based on DS/CDMA or OFDM‐MIMO [5–7]. They provide a superior, although computationally more expensive, alternative to conventional single‐sensor/user (matched filter) detection, which is seriously limited by MAI, multipath propagation in frequency‐selective channels, asynchronism, and accuracy, calibration and direction of arrival (DOA) errors. The use of antenna arrays offers the possibility to use the spatial characteristics of different user signals to augment the temporal discrimination provided by their signature sequences. This will lead to a spatial‐temporal detector [8]. Combined multi‐user beamforming algorithms for space‐time processing can be found in the literature [7–15].

In Chapter 8, we will present a combined multi‐user and beamforming processing approach for ...