Low-Complexity Two-Timescale Hybrid Precoding for mmWave Massive MIMO: A Group-and-Codebook Based Approach

In this paper, we present a novel hybrid precoding scheme, named group-and-codebook based two-timescale hybrid precoding (GC-THP), for reducing complexity in millimeter wave massive MIMO systems. The scheme clusters users into groups based on their statistical similarity and selects analog beams from a codebook with orthogonal beams. The base station time-shares among multiple analog precoders, each serving a subset of user groups, for fairness. At the slow timescale, the analog precoders, together with their corresponding group scheduling vectors and time-sharing factors, are jointly optimized, while at the fast timescale, short-term user scheduling and digital precoding are performed for a given analog precoder and its associated group scheduling vector. The proposed scheme employs beam-domain channel statistics with reduced dimension to optimize the proportional fairness utility. By applying user grouping and codebook based analog precoding, the proposed scheme significantly reduces complexity while retaining high performance levels. Moreover, the implementation complexity is tunable by adjusting the codebook size and the number of user groups, allowing for flexible performance-complexity tradeoffs. Simulation results confirm a superior performance-complexity tradeoff for the proposed GC-THP in comparison to the existing hybrid precoding schemes.