Beam-Selection-Based Statistical Beamforming for FDD Massive MIMO: Exploiting Spatial Reciprocity

In this paper, we study the beamforming design problem in frequency-division duplexing (FDD) massive MIMO downlink systems, where instantaneous channel state information (CSI) is unavailable at the base station (BS). We propose to extract the spatial information (i.e., the angle parameters and the large-scale fading coefficients) of the downlink channel from the uplink channel estimation procedure, based on which a novel downlink beamforming design is provided. Furthermore, we derive a sum-rate expression and its approximations for the proposed system. By maximizing the resultant sum-rate, we develop a low-complexity beam selection scheme. Numerical results demonstrate that our proposed algorithm has a significant improvement compared to the existing statistical beamforming (SBF) approaches.