The Interference Broadcast Channel with Reconfigurable Intelligent Surfaces: A Cooperative Sum-Rate Maximization Approach

TL;DR

This paper proposes a distributed optimization method for jointly designing precoding and RIS configurations in a multi-cell interference broadcast channel, enhancing sum-rate performance with RISs modeled as tunable meta-elements.

Contribution

It introduces a cooperative, distributed approach for sum-rate maximization in wideband interference channels with reconfigurable intelligent surfaces, considering frequency selectivity and beyond diagonal RIS structures.

Findings

Distributed algorithm converges efficiently.

Superiority over non-cooperative schemes.

Effective handling of frequency-selective RISs.

Abstract

This paper studies the interference broadcast channel comprising multiple multi-antenna Base Stations (BSs), each controlling a beyond diagonal Reconfigurable Intelligent Surface (RIS) and serving multiple single-antenna users. Wideband transmissions are considered with the objective to jointly design the BS linear precoding vectors and the phase configurations at the RISs in a distributed manner. We take into account the frequency selectivity behavior of each RIS's tunable meta-element, and focusing on the sum rate as the system's performance criterion, we present a distributed optimization approach that enables cooperation between the RIS control units and their respective BSs. According to the proposed scheme, each design variable can be efficiently obtained in an iterative parallel way with guaranteed convergence properties. Our simulation results demonstrate the validity of the presented distributed algorithm and showcase its superiority over a non-cooperative scheme as well as over the special case where the RISs have a conventional diagonal structure.