Hybrid Beamforming and Passive Reflection Design for RIS-Assisted mmWave MIMO Systems

Millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) communication systems with hybrid analog and digital beamforming architectures have emerged as a key enabling technique for providing very high date rate. Recently, reconfigurable intelligent surface (RIS) has been regarded as a revolutionary technology for future wireless communication systems owing to its capability of tailoring propagation environments. Thus, RIS technique is very promising and suitable for mmWave MIMO communications to tackle the inherent but fatal blockage problem. In this paper, we consider RIS-assisted mmWave MIMO systems, in which both the hybrid beamforming schemes at the transceivers and the RIS employ low-resolution phase shifters (PSs) for practical implementation. Our goal is to design active hybrid beamforming and passive RIS reflection to maximize the spectral efficiency. To this end, we propose to decouple the original problem and separately consider the passive RIS reflection and hybrid beamformer design. A successive refinement optimization method is first developed to design the reflection pattern of RIS. Then with the designed reflection matrix and the resulting effective channel, an efficient algorithm is introduced to solve the joint hybrid precoder and combiner design problem. Simulation results illustrate the significant performance improvement of our proposed hybrid beamforming and RIS reflection design algorithm compared with existing works.