Group-and-Codebook Based Two-Timescale Hybrid Precoding for mmWave Massive MIMO Systems

The paper presents a novel hybrid precoding scheme, named group-and-codebook based two-timescale hybrid precoding (GC-THP), for millimeter wave (mmWave) massive MIMO Systems. This scheme aims to reduce complexity by clustering users into groups based on their statistical similarity and selecting analog beams from a codebook containing orthogonal beams. To achieve fairness, the base station (BS) time-shares among multiple analog precoders, each serving a subset of user groups. 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 uses beam-domain channel statistics with reduced dimension to maximize the proportional fairness (PF) utility. By applying user grouping and codebook based analog precoding, the proposed scheme significantly reduces complexity while retaining high performance levels. Furthermore, the implementation complexity is tunable by adjusting the codebook size and the number of user groups, allowing for flexible performance-complexity trade-offs. Simulation results confirm a superior performance-complexity trade-off for the GC-THP than existing hybrid precoding schemes.