Faulty Yet Secure: Sum Secrecy Rate Optimization Under Faulty Reconfigurable Intelligent Surfaces

Abstract

Hardware faults in reconfigurable intelligent surfaces (RISs) disrupt their phase alignment and degrade control over the wireless channel, exposing systems to new physical layer security (PLS) vulnerabilities. Faulty reflecting elements, often triggered by manufacturing defects, aging, or environmental stress, distort beamforming, causing signal leakage that can be exploited by eavesdroppers. Despite this risk, existing studies have neither quantified the effect of such faults on the sum secrecy rate (SSR) nor developed mitigation strategies. To address this gap, we propose a solution (i.e., Fierse ) which jointly optimizes the base station (BS) precoder and RIS phase shifters to maximize the SSR under partial hardware faults. To further ensure fairness among user equipments (UEs), we exploit the leakage-aware property of the signal-to-leakage-and noise ratio (SLNR) formulation and develop two max-min SLNR schemes: one based on perfect channel state information (CSI) assumption and the other on statistical CSI. Simulation results show that Fierse preserves strong secrecy performance even with 86% faulty elements, achieving nearly 92% higher SSR than the fault-unaware baseline. The max-min SLNR schemes achieve approximately 32% of Fierse ’s secrecy performance while providing high fairness (Jain’s index ≈ 0.9 ) under about 62% faulty elements. Our findings demonstrate that fault-aware design is crucial for maintaining secrecy in RIS-assisted networks undergoing partial faults. Depending on system requirements, Fierse offers higher secrecy efficiency, whereas max-min SLNR schemes provide improved fairness and robustness.