Downlink Hybrid Precoding and User Selection for Multiuser MIMO-OFDM Systems

This paper studies hybrid precoding and user se-lection for a downlink multi-user massive multi-input and multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system, where a moderate number of radio-frequency (RF) chains are connected to a large number of antennas via an analog phase shifter network (PSN). We aim at maximizing the downlink sum-rate by optimizing the analog precoder, the digital zero-forcing (ZF) beamforming and the power allocation among different users and frequency subcarriers. Unlike the conventional methods which usually take use of the approx-imation of the sum-rate to achieve the analog and digital precoders as the sum-rate maximization problem is generally intractable and therefore cause some performance loss, in this paper, we propose an efficient and feasible method to solve the sum-rate maximization problem directly with comparable complexity. Another advantage of the proposed method is that it can simultaneously achieve the optimal user selection during the precoding and power allocating process without consuming additional complexity. Simulation results illustrate that the proposed method can outperform the state-of-the-art method significantly.