Double-IRS Assisted Multi-User MIMO: Cooperative Passive Beamforming Design

TL;DR

This paper investigates a double-IRS system with cooperative passive beamforming, demonstrating its potential to significantly enhance multi-user wireless communication performance over traditional single-IRS setups.

Contribution

It introduces a novel cooperative beamforming design for double-IRS systems, jointly optimizing active and passive beamforming to leverage inter-IRS channel gains.

Findings

Double-IRS system outperforms single-IRS in SNR and channel rank.

Analytical proof of performance superiority over conventional systems.

Simulation results confirm practical advantages of the proposed design.

Abstract

Intelligent reflecting surface (IRS) has emerged as an enabling technology to achieve smart and reconfigurable wireless communication environment cost-effectively. Prior works on IRS mainly consider its passive beamforming design and performance optimization without the inter-IRS signal reflection, which thus do not unveil the full potential of multi-IRS assisted wireless networks. In this paper, we study a double-IRS assisted multi-user communication system with the \emph{cooperative} passive beamforming design that captures the multiplicative beamforming gain from the inter-IRS channel. Under the general channel setup with the co-existence of both double- and single-reflection links, we jointly optimize the (active) receive beamforming at the base station (BS) and the cooperative (passive) reflect beamforming at the two distributed IRSs (deployed near the BS and users, respectively) to maximize the minimum signal-to-interference-plus-noise ratio (SINR) of all users. Moreover, for the single-user and multi-user setups, we analytically show the superior performance of the double-IRS cooperative system over the conventional single-IRS system in terms of the maximum signal-to-noise ratio (SNR) and multi-user effective channel rank, respectively. Simulation results validate our analytical results and show the practical advantages of the proposed double-IRS system with cooperative passive beamforming designs.