Multiple input multiple output (MIMO) techniques have gathered much attention in recent years as a way to improve drastically the performance of wireless mobile communications. The MIMO technique utilizes multiple antenna elements at the transmitter and the receiver to improve communication link quality and/or communication capacity. A MIMO system can provide two types of gain: spatial diversity gain and spatial multiplexing gain. Spatial diversity improves the reliability of communication in fading channels and spatial multiplexing increases the capacity by sending multiple streams of data in parallel through multiple spatial channels. Transmit eigen-beamforming (TxBF) with unitary precoding is a spatial multiplexing technique that utilizes the eigen-structure of the channel to generate independent spatial channels. Practical considerations of TxBF that affect the performance and the overhead of the system are precoder quantization/averaging and feedback delay.
In this chapter, we first give a general overview of MIMO concepts. In Section 6.3, we describe the parallel decomposition of a MIMO channel for narrowband and wideband transmission. We also illustrate the realization of MIMO spatial multiplexing in SC-FDMA. In Section 6.4, we introduce the SC-FDMA TxBF with unitary precoding technique and numerically analyze the link level performance with practical considerations. In Section 6.5, we describe the SC-FDMA spatial diversity schemes.