10.1 Introduction

In conventional wireless communication systems, one end of a link, typically the base station, is equipped with more than one antenna (e.g., two antennas for receive diversity or, more recently, an antenna array with more than two elements for beamforming or beam steering). Several chipset and handset vendors have recently started developing and designing phones with dual antennas for mobile receive diversity (MRD). In a MIMO system the communication link has both a transmitter as well as a receiver that are equipped with multiple antenna elements, as shown in Figure 10.1. The idea behind MIMO is to use AA at both the transmitter and receiver in combination with space-time modulation and coding techniques to achieve very high spectral efficiencies. The motivation for using such a setup is to achieve improvements that can be used to increase both the quality of service and the revenues significantly. Examples of applications that can benefit from MIMO systems include cellular/PCS system deployment based on fixed user terminals, microcells, picocells, and wireless LANs, as well as portable applications such as laptops and PDAs. Coding and modulation are essentially temporal techniques. A MIMO system is a space-time signal processing approach in which the time dimension is complemented with the spatial dimension through the use of multiple spatially distributed antennas. As such, MIMO systems can be viewed as an extension of smart antennas. Therefore, we can classify multiantenna schemes as a family that includes spatial techniques such as adaptive antennas, beamforming, and spatial diversity, as...