Introduction

Multiple antenna techniques (beyond two receive antennas at the base station) have now achieved a level of technical maturity that allows their implementation in commercial cellular systems. Specifically, multiple antenna technologies have been integrated into Third Generation (3G) cellular systems, and will soon be part of the 802.11n standard. In this chapter, we examine commercial implementations of multiple antenna techniques. While multiple antennas can be used at either the transmitter or the receiver, commercial standard specifications primarily focus on application at the transmitter. Multiple antenna techniques that are applied at the receiver are not specified by the standard and are vendor specific. As a result, while some of the techniques discussed in this chapter (e.g., transmit diversity) are defined by the 3G standards, others (e.g., receive beamforming) can be used in 3G systems, but are not specifically defined by standards-based technical specifications. Further, there are techniques that are under investigation in 3G standards bodies, e.g., spatial multiplexing, which requires multiple antennas at both the receiver and transmitter, often referred to as multiple input and multiple output (MIMO). We will describe techniques that fall into these categories, and will be careful to distinguish those techniques that are specified by the standard, that are under investigation by a specific standards group, or that are allowed by the standard. Section 25.2 presents the system model used throughout the chapter. Transmit diversity techniques are specified by both of the major 3G standards, and are discussed in detail in Section 25.3.