On the Robustness of RSMA to Adversarial BD-RIS-Induced Interference

TL;DR

This paper evaluates the robustness of RSMA in multi-user MISO systems against adversarial interference from BD-RISs, revealing vulnerabilities with perfect CSI and robustness advantages under imperfect CSI.

Contribution

It introduces attack strategies against RSMA with BD-RISs and compares its robustness to SDMA under different CSI conditions.

Findings

RSMA is vulnerable to attacks with perfect CSI, similar to SDMA.

BD-RIS can cause severe performance degradation in RSMA.

Under imperfect CSI, RSMA outperforms SDMA in robustness, especially at higher transmit powers.

Abstract

This article investigates the robustness of rate-splitting multiple access (RSMA) in multi-user multiple-input single-output (MISO) systems to interference attacks against channel acquisition induced by beyond-diagonal RISs (BD-RISs). Two primary attack strategies, random and aligned interference, are proposed for fully connected and group-connected reconfigurable intelligent surface (RIS) architectures. Valid random reflection coefficients are generated exploiting the Takagi factorization, while potent aligned interference attacks are achieved through optimization strategies based on a quadratically constrained quadratic program (QCQP) reformulation followed by projections onto the unitary manifold. Our numerical findings reveal that, when perfect channel state information (CSI) is available, RSMA behaves similarly to space-division multiple access (SDMA) and thus is highly susceptible to the attack, with BD-RIS inducing severe performance loss and significantly outperforming diagonal RIS. However, under imperfect CSI, RSMA consistently demonstrates significantly greater robustness than SDMA, particularly as the system's transmit power increases.