LTE Advanced: 3GPP Solution for IMT-Advanced

6.2 Downlink MIMO Enhancements Overview

Downlink MIMO operation in LTE is available already in Release 8 LTE specifications and widely used in the first phase LTE networks rolled out based on the principles shown in Chapter 3. Release 10 provides several new enhancements which can both improve the performance and further boost the achievable peak data rates in the downlink direction. The following key new areas are introduced on top of the Release 8 and 9 MIMO capabilities as shown in Figure 6.1.

Figure 6.1 Downlink MIMO development in different releases.

• Extension of the MIMO supports up to eight antennas with up to eight parallel data streams if eight transmitter and eight receiver antennas available (8 × 8 MIMO).
• Transmission with two, four or eight antennas and deriving the Precoding Matrix Indication (PMI)-related feedback based on the Channel State Information Reference Signals (CSI-RS)
• MIMO transmission with the use of UE-specific demodulation Reference Signal (URS) which are sent in the same physical resource blocks than the data for the given user.
• Optimization of the MIMO feedback, including the feedback for both Multi-user MIMO (MU-MIMO) and single user MIMO (SU-MIMO).

The design criteria of the enhancements was, on the other hand, to ensure backwards compatibility with the Release 8 and 9 MIMO operation, while also reducing the impact to the system performance when ...