Robust Consensus-Based Distributed Beamforming for Wideband Cell-free Multi-RIS MISO Systems

TL;DR

This paper proposes a decentralized beamforming scheme for wideband cell-free multi-RIS MISO systems, improving cooperation efficiency and robustness against imperfect channel information and frequency selectivity.

Contribution

It introduces a novel distributed optimization approach using consensus updates for RIS phase configuration, reducing cooperation overhead compared to centralized methods.

Findings

Distributed scheme outperforms centralized approaches in simulations

Effective in scenarios with imperfect channel information

Handles frequency selectivity of RIS elements efficiently

Abstract

The cell-free networking paradigm constitutes a revolutionary architecture for future generations of wireless networks, which has been recently considered in synergy with Reconfigurable Intelligent Surfaces (RISs), a promising physical-layer technology for signal propagation programmability. In this paper, we focus on wideband cell-free multi-RIS-empowered Multiple-Input Single-Output (MISO) systems and present a decentralized cooperative active and passive beamforming scheme, aiming to provide an efficient alternative towards the cooperation overhead of available centralized schemes depending on central processing unit. Considering imperfect channel information availability and realistic frequency selectivity behavior of each RIS's element response, we devise a distributed optimization approach based on consensus updates for the RISs' phase configurations. Our simulation results showcase that the proposed distributed design is superior to centralized schemes that are based on various Lorentzian-type wideband modeling approaches for the RISs.