1.1 Communications in Interference-Limited Environments

Generally, the performance of communication systems is limited by the interference, of which there are various sources. For example, multipaths of a radio channel cause intersymbol interference (ISI), as shown in Fig. 1.1. The received signal becomes a sum of delayed transmitted signals with different attenuation factors. Although the background noise is negligible, the ISI can degrade the performance because the received signal is distorted by the ISI.

Figure 1.1: Radio channel with multipaths. In this illustration, the propagation delay of the upper path is zero, while the propagation delay of the lower path is ? > 0. The received signal is a superposition of the multipath signals.

In a multiuser system, such as the one shown in Fig. 1.2, the other users signals become interfering signals. Thus, it is important to alleviate interfering signals to achieve a satisfactory performance.

Figure 1.2: Multiuser system.

Throughout this book, we introduce a few communication systems under interference-limited environments. For each communication system, adaptive and/or iterative signal processing methods are discussed to overcome...