Joint Transceiver and Reconfigurable Intelligent Surface Design for Multiuser mmWave MIMO Systems Relying on Non-Diagonal Phase Shift Matrices

The downlink of a reconfigurable intelligent surface (RIS)-aided multi-user (MU) millimeter wave (mmWave) multiple-input multiple-output (MIMO) system relying on non-diagonal RIS (NDRIS) phase shift matrix is considered. A max-min fairness (MMF) problem formulated under the total transmit power constraint while employing joint active hybrid beamforming (HBF) both at BS as well each user equipment (UE), and passive NDRIS. To solve this non-convex problem, sequential optimization method conceived, wherein UE having poorest channel identified first, which termed worst-case UE. Then shifter coefficients NDRIS are optimized using alternating direction multipliers (ADMM) followed by precoder (TPC) receiver combiner (RC) design Karcher mean, least squares regularized zero forcing (RZF) principles. Finally, optimal allocation computed path-following algorithm. Simulation results show that proposed NDRIS-HBF yields an improved rate in comparison to its conventional diagonal (DRIS)-HBF counterpart, approaching half-duplex relay (HDR)-HBF benchmark for large values number reflecting elements. Furthermore, energy efficiency (EE) structure significantly higher than DRIS, HDR systems, being achieved full-duplex (FDR) high SNR.