Simplified Robust Adaptive Detection and Beamforming for Wireless Communications

3Adaptive Detection Algorithms

3.1 Introduction

In this chapter, we will survey adaptive detection algorithms based on the DS/CDMA model. However, the adaptive techniques that are summarized in this survey can be easily extended to MIMO/OFDM and smart antenna arrays. The DS/CDMA model is the most complicated system model because of the need for multiuser interference cancellation and because the channel is frequency selective, as explained in Chapter 2. Despite the various advantages of the DS/CDMA system, it is interference limited due to multiuser interference and it cannot be easily extended to ultra‐broadband systems, as explained in Chapter 2. A conventional DS/CDMA receiver treats each user separately, as a signal, with other users considered as noise or multiple access interference (MAI). A major drawback of such conventional DS/CDMA systems is the near–far problem: degradation in performance due to the sensitivity to the power of desired user against interference power. Reliable demodulation is impossible unless tight power control algorithms are used. The near–far problem can significantly reduce the capacity. Multiuser detection (MUD) algorithms have been developed to improve capacity dramatically over that achievable with conventional single‐user detection techniques. MUD considers signals from all users, which lead us to joint detection. MUD reduces interference and hence leads to a capacity increase and alleviation of the near–far problem. Power control algorithms can ...