Product Codebook Feedback for Massive MIMO with Cross Polarized 2D Antenna Arrays

Massive MIMO involves the use of large scale antenna arrays for high-gain adaptive beamforming and high-order spatial multiplexing. An important design challenge in Massive MIMO systems is the acquisition of channel state information at the transmit array, where accurate channel knowledge is critical for obtaining the best performance with Multi-User MIMO transmission on the downlink. In this paper, we explore the use of a product codebook feedback methodology for two-dimensional antenna arrays where the codebook feedback strategy is decomposed into two separate feedback processes, one for azimuth and one for elevation. We specifically address the case where the transmit array consists of cross-polarized antennas and show how two separate codebook feedback processes can reduce reference signal overhead and simplify the mobile complexity while providing significant gains in performance over existing LTE configurations.