Feedback overhead reduction method for 3D MIMO precoding systems

For 3D MEMO precoding systems over spatially correlated channel, a novel limited feedback method is proposed by utilizing the nature of the spatial correlation and clustering of the subchannel of transmitting and receiving antenna pair. In this method, due to the co-phased and spatial-correlated characteristics of the vertical channel for 2D antenna array, each vertical antenna is assumed to have the same horizontal phase and all the horizontal channels only feedback one precoding matrix index (PMI), while the adjacent vertical channels are grouped into clusters and the subchannels in the same cluster use the same precoding vectors. Then an auxiliary bit is added in front of the horizontal and vertical PMI to classify the two type feedback bits. According to the feedback bits, the base station (BS) finds the horizontal and vertical precoding vectors, and re-constructs the 3D precoding matrix by expanding and pointing multiplication operation. The simulation results show that the method can obtain good bit error rate (BER) performance with reduced feedback overhead.