Multi-resolution codebook design for two-stage precoding in FDD massive MIMO networks

In this paper, we develop a new codebook design method for multi-resolution codebook based two-stage precoding scheme in massive MIMO networks in frequency division duplex (FDD) mode. A narrow-beam generated by each codeword is intended to provide coverage over certain beam range with strict constraints on the average and the variation in the radiated power. Each narrow-beam or codeword is designed based on a new performance metric, the ratio of the expected average power within the coverage beam range to that outside the beam range, i.e., beam-to-leakage ratio (BLR). An optimization problem for narrow-beam design is formulated to maximize the BLR. The codebook is generated via solving the optimization problem. Based on numerical evaluation, our novel codebook design based transmission scheme can improve the overall network throughput compared with the DFT-based and covariance based method when the angular spread of the channel is relative large or when the channel is rich scattering.