A Robust Quantized Beam-Squint and Interference Aware Statistical Beamforming for RIS-Aided Massive MIMO

This study investigates an interference-aware (IA) and beam-squint-aware (BSA) statistical reconfigurable intelligent surface (RIS) design that considers the practical amplitude-phase coupling for RIS-aided spatial wideband massive multiple-input multiple-output (MIMO) systems. First, we find the optimal ideal IA-BSA statistical frequency-independent and hypothetical frequency-dependent RIS designs, which are based on maximizing the signal-to-interference-and-noise ratio (SINR) and statistical mutual information (SMI), respectively. In these unconstrained designs, the amplitudes and phases of the RIS elements are assumed to take arbitrary values independently. Second, we propose a frequency-independent statistical quantized IA-BSA RIS beamforming based on the mean SMI maximization considering the amplitude-phase coupling of the practical RIS structures. The proposed practical constrained design is obtained by a computationally efficient iterative phase refinement (IPR) algorithm based on alternating optimization (AO). The computational complexity of the proposed RIS design is presented, and its performance is evaluated in terms of beam pattern, outage capacity, and spectral efficiency (SE).