Mix-and-Conquer: Beamforming Design with Interconnected RIS for Multi-User Networks

TL;DR

This paper introduces an interconnected RIS (I-RIS) structure with binary RF switches for multi-user networks, offering higher gain and compactness compared to traditional RIS, with optimized beamforming methods evaluated for performance.

Contribution

The paper presents a novel interconnected RIS design with binary switches and develops two optimization algorithms for beamforming in multi-user scenarios.

Findings

I-RIS achieves higher gain than standard RIS.

The compact I-RIS is suitable for space-limited deployment.

Optimization methods improve sum-rate performance.

Abstract

We propose a new reconfigurable intelligent surface (RIS) structure, referred to as interconnected RIS (I-RIS), which allows the RIS elements to be interconnected and share the incident signals using simple binary radio frequency (RF) switches and mix them into the reflecting signals. This structure enables multi-user scaling and requires fewer elements (i.e., a compact structure) compared to standard RIS (S-RIS), which assumes no interconnection between the elements. The I-RIS compact design makes it practical for deployment on space-limited nodes, e.g., unmanned aerial vehicles (UAVs). Hence, in this work, we propose a beamforming design based on I-RIS in a multi-user network, where we use binary RF switches as RIS elements. We show that our switch-based I-RIS offers a higher gain compared to an S-RIS using phase shifters. Finally, we introduce two optimization methods, sigmoid filled function (SFF) and semi-definite binary optimization (SBO), to optimize the RIS elements and evaluate their performance in terms of sum-rate and complexity.