Security-Spectral Efficiency Tradeoff in STAR-RIS RSMA: A Max-Min Fairness Framework

2026-03-27

AI Summary

This work addresses the security–efficiency trade-off in a STAR-RIS-assisted RSMA system coexisting with both internal and external eavesdroppers by proposing a max–min fairness optimization framework under secrecy constraints. The proposed approach jointly optimizes transmit beamforming and STAR-RIS phase shifts, and for the first time exploits the RSMA common stream to impose differentiated interference on internal and external eavesdroppers, thereby enabling a synergistic enhancement of both secrecy and spectral efficiency. Simulation results demonstrate that the proposed scheme significantly improves system spectral efficiency and fairness among legitimate users while satisfying stringent secrecy rate requirements.

Abstract

Simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) enable full-space coverage but also expose wireless transmissions to security from multiple spatial directions. This paper investigates a STAR-RIS-assisted secure RSMA system where both internal and external eavesdroppers may coexist in the transmission and reflection regions. In such a scenario, the RSMA common stream simultaneously serves legitimate users, impairs external eavesdroppers, and avoids assisting internal eavesdroppers, leading to a challenging trade-off between spectral efficiency and confidentiality. To address this issue, we formulate a max-min fairness problem under secrecy constraints and develop an iterative algorithm to jointly optimize transmit beamforming and STAR-RIS phase shifts. Simulation results demonstrate that the proposed scheme improves spectral efficiency while maintaining confidentiality.

Problem

• STAR-RIS
• RSMA
• physical layer security
• spectral efficiency
• eavesdropping

Innovation

• STAR-RIS
• RSMA
• physical layer security
• max-min fairness
• beamforming optimization