Adaptive feedback rate control for massive MIMO system in LTE

The increased number of antennas for massive MIMO system implies that the quantization codebook size needs to be significantly larger, which increases precoder search complexity accordingly. This paper compares the vertical/horizontal channel characteristics and finds that the vertical channel has a much longer coherence time than the horizontal channel. Based on these results, a two-dimension CSI quantization mechanism is proposed to allow decoupled vertical/horizontal domain quantization. The mechanism allows the vertical domain precoder search to be implemented at a slower rate than the horizontal domain, thereby enabling the network to separately control the feedback rate/granularity in different spatial dimensions. The proposed mechanism achieves significant UE complexity reduction and power consumption without compromising the system performance, demonstrated by realistic system simulation.