Movable Beyond-Diagonal Reconfigurable Intelligent Surfaces: Moving, Interconnecting, or Both?

TL;DR

This paper introduces a movable beyond-diagonal reconfigurable intelligent surface (MA-BD-RIS) that enhances wireless channels by combining movability and inter-element connectivity, optimizing system performance in various scenarios.

Contribution

It proposes a novel MA-BD-RIS design with joint optimization of beamforming, configuration, and placement, along with an efficient algorithm for implementation.

Findings

High-movability structures excel in small-scale RIS scenarios.

High-connectivity structures outperform in large-scale RIS and massive MIMO.

The proposed approach significantly improves sum-rate performance.

Abstract

This letter proposes a movable beyond-diagonal reconfigurable intelligent surfaces (MA-BD-RIS) design, combining inter-element connectivity and movability for channel enhancement. We study a MA-BD-RIS assisted multi-user multiple input single output system where beamforming, BD-RIS configuration, and elements positions are jointly optimized to maximize the sum-rate. An efficient algorithm is developed, incorporating closed-form beamforming, a low-complexity partially proximal alternating direction method of multipliers for BD-RIS design, and successive convex approximation for element placement. Simulations show that the high-movability structure yields superior performance in small-scale RIS and rich scattering scenarios, while the high-connectivity structure dominates in large-scale RIS and massive transmit array configurations.