Wireless Communications

13Wireless MIMO Systems

Abstract

The abnormal capacity inherent in multi-input multi-output (MIMO) fading channels makes it possible to implement high-speed wireless transmission, as demonstrated by Telatar and Foschini. One major challenge is the inter-antenna (or cross-antenna) interference (IAI) caused by spatial correlation among antennas. The idea used to combat inter-symbol interference arising in temporally dispersive channels is also applied to MIMO systems. Various possible transceivers that tackle IAI are derived and analyzed in this chapter under different criteria such as maximal mutual information, zero forcing, and minimum mean-square error (MMSE). The difference is that spatial correlation usually does not possess a Toeplitz structure.

A more aggressive strategy to combat IAI, however, is to eliminate its source of generation. Alamouti achieves this goal by introducing temporal orthogonality at the transmitter, which is virtually converted into equivalent independent channels at the receiver whereby the IAI is completely eliminated. More generally, the IAI problem automatically vanishes if we adopt a different philosophy of treating a set of parallel-transmitted data streams as a single matrix symbol. A MIMO channel is of multiple degrees of freedom (DF), which can be converted into higher data rate or into transmission reliability. The tradeoff between the two is also discussed.

13.1 Introduction

As mobile units move around a ground surface, scatterers such ...