Chapter 29
Multiple Antenna Techniques for LTE-Advanced
Multiple antenna techniques play a key role in LTE-Advanced. In the downlink, the goals are to support higher data rates than LTE Releases 8 and 9 through high-order Single-User Multiple-Input Multiple-Output (SU-MIMO), and higher spectral efficiency via enhanced Multi-User MIMO (MU-MIMO) techniques. To support these advances, new reference signals and enhanced UE feedback are introduced. In the uplink, SU-MIMO is introduced, and the control channel performance is enhanced using transmit diversity.
This chapter explains the techniques adopted for Release 10 and gives some insight into additional MIMO enhancement features that may be developed in future releases of LTE-Advanced.
29.1 Downlink Reference Signals
As discussed in detail in Section 8.2, LTE Release 8 provides cell-specific Reference Signals (RSs), also known as Common Reference Signals (CRSs) for up to 4 antenna ports. Cell-specific RSs are used by UEs both to perform channel estimation for demodulation of data and to derive feedback on the quality and spatial properties of the downlink radio channel. Together with signalling of the precoder used for data transmissions to the UE, the four cell-specific RS ports enable spatial multiplexing of up to four layers using codebook-based precoding, as explained in Section 11.2.2.2. LTE Release 9 additionally supports two-layer beamforming spatial ...
