Limited feedback precoding based on CSI-RS for 3D MIMO systems

Future fifth generation (5G) mobile networks will greatly increase the date-rate of communication. Three-dimensional (3D) multiple input multiple output (MIMO) systems have drawn more and more attention as they meet the increasing date-rate demands in 5G mobile networks. However, in the practical system, the large overhead of the channel state information-reference signal (CSI-RS) would become a barrier for performance improvement of 3D MIMO system with the significantly increased number of transmit antennas. What's more, it will be inefficient for performance promotion that the antenna elements (AEs) in one column are usually virtualized as one antenna port to support one date stream in the vertical direction in existing 3D MIMO. To overcome these problems, on the one hand, this paper proposes linked precoding, combining separate elevation CSI-RS configuration and CSI-RS precoded with elevation beamforming vector to make a better tradeoff between resource overhead and throughput performance, and on the other hand, multi-stream precoding based on CSI-RS is also proposed to provide larger throughput performance supporting multi-stream precoding not only in horizontal direction but also in vertical direction.