Joint Active and Passive Beamforming Optimization for Beyond Diagonal RIS-aided Multi-User Communications

TL;DR

This paper proposes an efficient optimization framework for beyond-diagonal RIS in multi-user MIMO systems, achieving near-optimal beamforming with reduced computational complexity through an iterative closed-form solution approach.

Contribution

It introduces a novel alternating optimization algorithm for joint active and passive beamforming in BD-RIS, improving efficiency over existing methods.

Findings

Significantly reduces computational complexity.

Achieves near-optimal sum rate performance.

Demonstrates effectiveness through numerical simulations.

Abstract

Benefiting from its capability to generalize existing reconfigurable intelligent surface (RIS) architectures and provide additional design flexibility via interactions between RIS elements, beyond-diagonal RIS (BD-RIS) has attracted considerable research interests recently. However, due to the symmetric and unitary passive beamforming constraint imposed on BD-RIS, existing joint active and passive beamforming optimization algorithms for BD-RIS either exhibit high computational complexity to achieve near optimal solutions or rely on heuristic algorithms with substantial performance loss. In this paper, we address this issue by proposing an efficient optimization framework for BD-RIS assisted multi-user multi-antenna communication networks. Specifically, we solve the weighted sum rate maximization problem by introducing a novel beamforming optimization algorithm that alternately optimizes active and passive beamforming matrices using iterative closed-form solutions. Numerical results demonstrate that our algorithm significantly reduces computational complexity while ensuring a sub-optimal solution.