Secrecy Performance Analysis of Multi-Functional RIS-Assisted NOMA Networks

TL;DR

This paper investigates how a novel multi-functional RIS can significantly improve the physical layer secrecy performance in NOMA networks, addressing coverage and fading challenges, and analyzing various practical impairments.

Contribution

It introduces a multi-functional RIS for enhanced secrecy in NOMA, deriving analytical expressions for SOP and throughput, and analyzing the effects of hardware limitations and imperfect SIC.

Findings

MF-RIS outperforms active RIS and TS-RIS in secrecy performance.

Residual interference from imperfect SIC dominates thermal noise at high SNR.

Adding elements to MF-RIS boosts secrecy against external eavesdroppers.

Abstract

Although reconfigurable intelligent surface (RIS) can improve the secrecy communication performance of wireless users, it still faces challenges such as limited coverage and double-fading effect. To address these issues, in this paper, we utilize a novel multi-functional RIS (MF-RIS) to enhance the secrecy performance of wireless users, and investigate the physical layer secrecy problem in non-orthogonal multiple access (NOMA) networks. Specifically, we derive the secrecy outage probability (SOP) and secrecy throughput expressions of users in MF-RIS-assisted NOMA networks with external and internal eavesdroppers. The asymptotic expressions for SOP and secrecy diversity order are also analyzed under high signal-to-noise ratio (SNR) conditions. Additionally, we examine the impact of receiver hardware limitations and error transmission-induced imperfect successive interference cancellation (SIC) on the secrecy performance. Numerical results indicate that: i) under the same power budget, the secrecy performance achieved by MF-RIS significantly outperforms active RIS and simultaneously transmitting and reflecting RIS; ii) with increasing power budget, residual interference caused by imperfect SIC surpasses thermal noise as the primary factor affecting secrecy capacity; and iii) deploying additional elements at the MF-RIS brings significant secrecy enhancements for the external eavesdropping scenario, in contrast to the internal eavesdropping case.