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

TL;DR

This paper explores the security and spectral efficiency tradeoff in STAR-RIS-assisted RSMA systems, proposing an optimization framework to enhance secrecy and performance.

Contribution

It introduces a max-min fairness optimization for secure STAR-RIS RSMA, jointly optimizing beamforming and phase shifts to balance security and spectral efficiency.

Findings

Proposed iterative algorithm improves spectral efficiency under secrecy constraints.

Simulation results show enhanced security without sacrificing spectral efficiency.

The framework effectively manages internal and external eavesdropper threats.

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.