Beyond-Diagonal RIS Prototype and Performance Evaluation

2025-05-19

AI Summary

This work addresses the limited degrees of freedom (DoFs) in conventional diagonal reconfigurable intelligent surfaces (RISs). We propose and experimentally realize the first reflective beyond-diagonal RIS (BD-RIS) prototype enabling dynamic inter-element connections. By integrating tunable load networks, antenna ports can be independently loaded or interconnected with adjacent elements; channel enhancement from such interconnection is validated in rich multipath environments. We establish the first mutual-coupling-aware BD-RIS modeling and optimization framework. Experimental results demonstrate that element interconnection significantly increases channel rank and effective DoFs; hardware non-idealities—including parasitic coupling and component losses—emerge as key performance bottlenecks; and mutual-coupling-aware optimization is essential to fully unlock the potential of interconnection. This work introduces a new paradigm for overcoming RIS hardware constraints and enhancing physical-layer programmability.

Technology Category

• Intelligent Robots: Learning & Optimization for ROB
• Search and Optimization: Mixed Discrete/Continuous Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

Abstract

We present the first experimental prototype of a reflective beyond-diagonal reconfigurable intelligent surface (BD-RIS), i.e., a RIS with reconfigurable inter-element connections. Our BD-RIS consists of an antenna array whose ports are terminated by a tunable load network. The latter can terminate each antenna port with three distinct individual loads or connect it to an adjacent antenna port. Extensive performance evaluations in a rich-scattering environment validate that inter-element connections are beneficial. Moreover, we observe that our tunable load network's mentioned hardware constraints significantly influence, first, the achievable performance, second, the benefits of having inter-element connections, and, third, the importance of mutual-coupling awareness during optimization.

Problem

• Experimental prototype of reflective beyond-diagonal RIS
• Impact of inter-element connections on performance
• Influence of hardware constraints on optimization

Innovation

• Reflective beyond-diagonal RIS prototype
• Tunable load network for antenna ports
• Inter-element connections enhance performance