ABSTRACT
Systems with multiple antennas can exploit, besides the usual time and frequency, the spatial dimension, with large improvements in terms of diversity, interference mitigation, and throughput. For this reason, they are among the key technologies in modern wireless transmission systems. This chapter focuses on multiple-input multiple-output (MIMO) wireless systems, but several of the described techniques can also be applied in wired systems. It describes systems with multiple antennas for diversity and interference mitigation. The chapter summarizes some characteristics of MIMO channels. The enhanced robustness to co-channel interference increases the number of served users per unit area in wireless cellular systems. Multiple antennas have also the important advantage of mitigating co-channel interference. Diversity is used to reduce the variations of the signal-to-noise ratio level due to fading, by sending each information symbol through different channels with independent fading levels, and then combining the outputs.
