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Physical Layer Security in FAS-aided Wireless Powered NOMA Systems

Farshad Rostami Ghadi, Masoud Kaveh, Kai-Kit Wong, Diego Martin, Riku Jantti, Zheng Yan

TL;DR

The paper addresses the security of fluid antenna system (FAS)-assisted wireless powered communication networks (WPCNs) implementing non-orthogonal multiple access (NOMA) under external and internal eavesdropping. It models the equivalent FAS channels using Gaussian copulas, and computes secrecy metrics—secrecy outage probability (SOP) and average secrecy capacity (ASC)—via Gauss-Laguerre and Gauss-Legendre quadrature, demonstrating robustness gains over traditional TAS. The key contributions include a novel FAS-enabled secure WPCN framework, analytical characterizations of the FAS channel distributions, and compact, quadrature-based expressions for SOP and ASC under both eavesdrodropping scenarios. The results show that increasing the number and size of fluid antenna ports reduces secrecy outages and increases secrecy capacity, highlighting the practical impact of FAS in secure, energy-efficient 6G networks.

Abstract

The rapid evolution of communication technologies and the emergence of sixth-generation (6G) networks have introduced unprecedented opportunities for ultra-reliable, low-latency, and energy-efficient communication. However, the integration of advanced technologies like non-orthogonal multiple access (NOMA) and wireless powered communication networks (WPCNs) brings significant challenges, particularly in terms of energy constraints and security vulnerabilities. Traditional antenna systems and orthogonal multiple access schemes struggle to meet the increasing demands for performance and security in such environments. To address this gap, this paper investigates the impact of emerging fluid antenna systems (FAS) on the performance of physical layer security (PLS) in WPCNs. Specifically, we consider a scenario in which a transmitter, powered by a power beacon via an energy link, transmits confidential messages to legitimate FAS-aided users over information links while an external eavesdropper attempts to decode the transmitted signals. Additionally, users leverage the NOMA scheme, where the far user may also act as an internal eavesdropper. For the proposed model, we first derive the distributions of the equivalent channels at each node and subsequently obtain compact expressions for the secrecy outage probability (SOP) and average secrecy capacity (ASC), using the Gaussian quadrature methods. Our results reveal that incorporating the FAS for NOMA users, instead of the TAS, enhances the performance of the proposed secure WPCN.

Physical Layer Security in FAS-aided Wireless Powered NOMA Systems

TL;DR

The paper addresses the security of fluid antenna system (FAS)-assisted wireless powered communication networks (WPCNs) implementing non-orthogonal multiple access (NOMA) under external and internal eavesdropping. It models the equivalent FAS channels using Gaussian copulas, and computes secrecy metrics—secrecy outage probability (SOP) and average secrecy capacity (ASC)—via Gauss-Laguerre and Gauss-Legendre quadrature, demonstrating robustness gains over traditional TAS. The key contributions include a novel FAS-enabled secure WPCN framework, analytical characterizations of the FAS channel distributions, and compact, quadrature-based expressions for SOP and ASC under both eavesdrodropping scenarios. The results show that increasing the number and size of fluid antenna ports reduces secrecy outages and increases secrecy capacity, highlighting the practical impact of FAS in secure, energy-efficient 6G networks.

Abstract

The rapid evolution of communication technologies and the emergence of sixth-generation (6G) networks have introduced unprecedented opportunities for ultra-reliable, low-latency, and energy-efficient communication. However, the integration of advanced technologies like non-orthogonal multiple access (NOMA) and wireless powered communication networks (WPCNs) brings significant challenges, particularly in terms of energy constraints and security vulnerabilities. Traditional antenna systems and orthogonal multiple access schemes struggle to meet the increasing demands for performance and security in such environments. To address this gap, this paper investigates the impact of emerging fluid antenna systems (FAS) on the performance of physical layer security (PLS) in WPCNs. Specifically, we consider a scenario in which a transmitter, powered by a power beacon via an energy link, transmits confidential messages to legitimate FAS-aided users over information links while an external eavesdropper attempts to decode the transmitted signals. Additionally, users leverage the NOMA scheme, where the far user may also act as an internal eavesdropper. For the proposed model, we first derive the distributions of the equivalent channels at each node and subsequently obtain compact expressions for the secrecy outage probability (SOP) and average secrecy capacity (ASC), using the Gaussian quadrature methods. Our results reveal that incorporating the FAS for NOMA users, instead of the TAS, enhances the performance of the proposed secure WPCN.
Paper Structure (18 sections, 6 theorems, 46 equations, 6 figures)

This paper contains 18 sections, 6 theorems, 46 equations, 6 figures.

Table of Contents

  1. Introduction
  2. Related Works
  3. Motivations and Contributions
  4. Organization
  5. Notation
  6. System Model
  7. Channel Model
  8. NOMA-FAS Scheme
  9. Secrecy Performance Analysis
  10. SOP Analysis
  11. Statistical Characteristics
  12. External Eavesdropping
  13. Internal Eavesdropping
  14. ASC Analysis
  15. External Eavesdropping
  16. ...and 3 more sections

Key Result

Theorem 1

The SOP expressions of the near user $\mathrm{u_n}$ and the far user $\mathrm{u_n}$ in the proposed FAS-aided secure WPCN under the external eavesdropping scenario are given by eq-sop-n and eq-sop-f, respectively, where $\nu_m = \frac{\overline{R}_\mathrm{n}\left(\overline{\gamma}_\mathrm{e}p_\mathr

Figures (6)

  • Figure 1: System model: FAS-aided secure NOMA WPCN.
  • Figure 2: The external SOP of user $i$ versus the average SNR $\overline{\gamma}_i$ when $\overline{\gamma}_\mathrm{e}=0$dB.
  • Figure 3: The internal SOP of user $\mathrm{u_n}$ versus the average SNR $\overline{\gamma}_{\mathrm{u_n}}$ when $N_{\mathrm{u_f}}=4$ and $W_{\mathrm{u_f}}=1\lambda^2$.
  • Figure 4: The SOP of user $i$ versus the secrecy rate $R_{\mathrm{s},i}$ when $N_{j}=4$ and $W_{j}=1\lambda^2$.
  • Figure 5: The external ASC of user $i$ versus the average SNR $\overline{\gamma}_i$.
  • ...and 1 more figures

Theorems & Definitions (10)

  • Theorem 1
  • proof
  • Lemma 1
  • Theorem 2
  • proof
  • Theorem 3
  • proof
  • Lemma 2
  • Theorem 4
  • proof