In this section the benefits from the downlink MIMO operation aggregation are investigated, both theoretically and also based on the simulations. The following areas are improved:
- Higher peak data rate,
- Improved capacity.
The higher peak data is obviously enabled with the addition of the number of parallel transmission streams numbering up to eight. With a 20 MHz carrier, thus the peak data rate would be increase from the 150 Mbps with 2 × 2 MIMO, all the way to the 600 Mbps with 8 × 8 MIMO, while the data rate with the 4 × 4 MIMO is 300 Mbps. Use of 8 × 8 MIMO would allow the theoretical data rate of up to 3 Gbps with the use of up to five carriers.
Two downlink MIMO features in LTE-Advanced need to be highlighted as providing improved capacity:
- Enhanced support for MU-MIMO operation;
- UE feedback for eight transmitter antenna.
The enhanced MU-MIMO support is obtained by using UE specific reference signals. This allows for full flexibility in allocating PRBs amongst users and also allows for optimized precoding which potentially can reduce interference amongst co-scheduled users. The performance improvement is most obvious with co-polar antennas at the eNodeB where a significant gain over the optimal Release 8 transmission scheme can be obtained already in case of four transmitter antenna, see Figure 6.8.
For cross-polar antennas, which are typically ...