5.1 Introduction

Multiple-input, multiple-output (MIMO) techniques have been integrated as one of the key approaches to provide the peak data rate, average throughput, and system performance in 3rd Generation Partnership Project (3GPP) long term evolution (LTE). Based on the function of the multiple transmission symbol streams in MIMO, the operation mode of multiple transmit antennas at the cell site (denoted as MIMO mode) have spatial division multiplexing (SDM), preceding, and transmit diversity (TD). Base on the allocation of the multiple transmission streams in MIMO, the MIMO mode is denoted as single user (SU)-MIMO if the multiple transmission symbol stream is solely assigned to a single UE and multiuser (MU)-MIMO if the SDM of the modulation symbol streams for different UEs use the same time-frequency resource [1]. The LTE downlink is an orthogonal frequency division multiplexing (OFDM) system, so the MIMO modes proposed in LTE are MIMO OFDM schemes.

In 3GPP LTE, the MIMO mode is restricted by the UE capability (e.g., number of receive antennas) and is determined by taking into account the slow channel variation. The MIMO mode is adapted slowly (e.g., only at the beginning of communication or every several 100 ms), in order to reduce the control signaling (including feedback) required to support the MIMO mode adaptation. For the control channel, only a single stream using the multiple transmit antennas is supported. The function of the MIMO in the general downlink physical channels is shown in Figure 5.1. The baseband signal processing...