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

Yingjie Pei, Wanli Ni, Jin Xu, Xinwei Yue, Xiaofeng Tao, Dusit Niyato

TL;DR

This work addresses secrecy in MF-RIS–assisted NOMA networks by deriving the secrecy outage probability and secrecy throughput under both external and internal eavesdropping in ES mode, and by providing high-SNR asymptotics and secrecy-diversity analyses. The authors develop a comprehensive statistical framework for legitimate cascaded channels and eavesdropping links, employing Laguerre/Lagrange quadrature techniques to obtain tractable SOP expressions that incorporate hardware impairments and imperfect SIC. Key findings show MF-RIS outperforms STAR-RIS and active RIS under the same power budget, with secrecy improvements scaling with the number of MF-RIS elements in external eavesdropping, while internal eavesdropping limits such gains due to the I-Eve’s beamforming advantage. The results offer practical guidance on ES coefficient design, power budgeting, and element count to maximize secrecy performance in 6G-like MF-RIS–NOMA networks, accounting for residual interference and hardware constraints.

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.

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

TL;DR

This work addresses secrecy in MF-RIS–assisted NOMA networks by deriving the secrecy outage probability and secrecy throughput under both external and internal eavesdropping in ES mode, and by providing high-SNR asymptotics and secrecy-diversity analyses. The authors develop a comprehensive statistical framework for legitimate cascaded channels and eavesdropping links, employing Laguerre/Lagrange quadrature techniques to obtain tractable SOP expressions that incorporate hardware impairments and imperfect SIC. Key findings show MF-RIS outperforms STAR-RIS and active RIS under the same power budget, with secrecy improvements scaling with the number of MF-RIS elements in external eavesdropping, while internal eavesdropping limits such gains due to the I-Eve’s beamforming advantage. The results offer practical guidance on ES coefficient design, power budgeting, and element count to maximize secrecy performance in 6G-like MF-RIS–NOMA networks, accounting for residual interference and hardware constraints.

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.
Paper Structure (26 sections, 11 theorems, 50 equations, 9 figures)

This paper contains 26 sections, 11 theorems, 50 equations, 9 figures.

Table of Contents

  1. Introduction
  2. Motivations
  3. Contributions
  4. System Model
  5. Network Descriptions
  6. Channel Characteristics
  7. Signal Model
  8. Wiretapping Scenarios
  9. External Wiretapping Scenario
  10. Internal Wiretapping Scenario
  11. Statistical Properties for Channels
  12. Statistical Properties for Legitimate Channels
  13. Statistical Properties for Eavesdropping Channels
  14. Secrecy Outage Probability Analysis
  15. External Wiretapping Scenario
  16. ...and 11 more sections

Key Result

Lemma 1

Upon utilizing the coherent phase-shifting scheme, the CDF and PDF of ${\left| {{{{\mathbf{\hat{H}}}}_{b\varphi }}} \right|^2}$ for $u_\varphi$ can be given as and where $\gamma \left( {a,x} \right) = \int_0^x {{p^{a - 1}}{e^{ - p}}dp}$ indicates the lower incomplete Gamma function gradvstejn2000table and $\Gamma \left( x \right) = \int_0^\infty {{e^{ - p}}{p^{x - 1}}dp}$ represents the Gamma f

Figures (9)

  • Figure 1: An illustration of MF-RIS-secured NOMA networks.
  • Figure 2: The SOP performance versus the total power budget in the external wiretapping scenario, where M = 12, ${e_r}$ = 0.8, ${e_t}$ = 0.2, ${a_r}$ = 0.25 and ${a_t}$ = 0.75.
  • Figure 3: The SOP performance versus the number of reconfigurable elements in the external wiretapping scenario, where ${e_r}$ = 0.8, ${e_t}$ = 0.2, ${a_r}$ = 0.3 and ${a_t}$ = 0.7.
  • Figure 4: The SOP performance versus the total power budget and ES coefficients in the external wiretapping scenario, where M = 12, ${a_r}$ = 0.25 and ${a_t}$ = 0.75.
  • Figure 5: The secrecy throughput performance versus the total power budget in the external wiretapping scenario, where M = 12, ${e_r}$ = 0.8, ${e_t}$ = 0.2, ${a_r}$ = 0.25 and ${a_t}$ = 0.75.
  • ...and 4 more figures

Theorems & Definitions (19)

  • Lemma 1
  • proof
  • Lemma 2
  • proof
  • Theorem 1
  • proof
  • Corollary 1
  • Theorem 2
  • Corollary 2
  • proof
  • ...and 9 more