Enhanced CSI Feedback for FD-MIMO with Beamformed CSI-RS in LTE-A Pro Systems

In this paper an enhanced channel state information (CSI) feedback scheme is proposed for full-dimension multiple-input multiple-output (FD-MIMO) systems based on beamformed channel state information reference signals (CSI-RS). To increase the spatial granularity of the beams used for data transmission and reduce the overhead in the downlink associated with beamformed CSI-RS transmission, a linear beam combining codebook is proposed. System-level performance evaluation of the proposed scheme is carried out and the performance is compared with the conventional beam selection codebook supported in LTE-A Pro Release 13 for Class B FD-MIMO systems. The proposed codebook shows significant performance improvement over the conventional codebook with reasonable increase in CSI feedback overhead and precoding matrix search complexity.