Transmitter Side Beyond-Diagonal Reconfigurable Intelligent Surface for Massive MIMO Networks

TL;DR

This paper proposes a novel BD-RIS deployment at the BS in massive MIMO networks, optimizing its coefficients via a manifold algorithm to enhance spectral efficiency based on statistical CSI.

Contribution

It introduces a beyond-diagonal RIS configuration at the transmitter side and develops a manifold-based optimization method for spectral efficiency maximization.

Findings

Significant spectral efficiency improvements demonstrated.

Effective optimization of BD-RIS coefficients based on statistical CSI.

Comparison shows advantages over conventional MaMIMO transmission.

Abstract

This letter focuses on a transmitter or base station (BS) side beyond-diagonal reflecting intelligent surface (BD-RIS) deployment strategy to enhance the spectral efficiency (SE) of a time-division-duplex massive multiple-input multiple-output (MaMIMO) network. In this strategy, the active antenna array utilizes a BD-RIS at the BS to serve multiple users in the downlink. Based on the knowledge of statistical channel state information (CSI), the BD-RIS coefficients matrix is optimized by employing a novel manifold algorithm, and the power control coefficients are then optimized with the objective of maximizing the minimum SE. Through numerical results we illustrate the SE performance of the proposed transmission framework and compare it with that of a conventional MaMIMO transmission for different network settings.