Coordinated Hybrid Beamforming for Millimeter Wave Multi-User Massive MIMO Systems

Massive Millimeter Wave (mmWave) Multiple Input Multiple Output (MIMO) systems utilize hybrid beamforming techniques to alleviate the implementation complexity of combining a large number of antennas. To solve the optimization problem in the hybrid design supporting multiple users and multiple data streams per user, we first propose a coordinated Radio Frequency (RF) beamforming technique based on the Generalized Low Rank Approximation of Matrices (GLRAM) approach and then develop an efficient Modified GLRAM (MGLRAM) algorithm. The proposed scheme only requires the information of the composite channel, instead of the complete physical channel matrix which is assumed to be known in the existing literature. It takes advantage of the coordination between the base station and users to achieve a maximal array gain and has no dimensionality constraint. The multiplexing gain is then exploited by applying the Block Diagonalization (BD) technique. It is shown that our proposed scheme is a practical and competing solution, which can be easily applied to both the Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems.