A Low-Complexity Beamforming Design for Beyond-Diagonal RIS aided Multi-User Networks

TL;DR

This paper introduces a low-complexity beamforming design for beyond-diagonal RIS in multi-user networks, providing a closed-form solution and a two-stage framework to improve sum-rate with reduced computation.

Contribution

It presents a novel closed-form passive beamforming solution and a two-stage joint active-passive beamforming framework for BD-RIS aided networks, enhancing efficiency and sum-rate.

Findings

Achieves higher sum-rate compared to existing algorithms.

Requires less computational time.

Demonstrates practical feasibility of the proposed method.

Abstract

Beyond-diagonal reconfigurable intelligent surface (BD-RIS) has been proposed recently as a novel and generalized RIS architecture that offers enhanced wave manipulation flexibility and large coverage expansion. However, the beyond-diagonal mathematical model in BD-RIS inevitably introduces additional optimization challenges in beamforming design. In this letter, we derive a closed-form solution for the BD-RIS passive beamforming matrix that maximizes the sum of the effective channel gains among users. We further propose a computationally efficient two-stage beamforming framework to jointly design the active beamforming at the base station and passive beamforming at the BD-RIS to enhance the sum-rate for a BD-RIS aided multi-user multi-antenna network.Numerical results show that our proposed algorithm achieves a higher sum-rate while requiring less computation time compared to state-of-the-art algorithms. The proposed algorithm paves the way for practical beamforming design in BD-RIS aided wireless networks.