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Secrecy Performance Analysis of RIS-Aided Fluid Antenna Systems

Farshad Rostami Ghadi, Kai-Kit Wong, Masoud Kaveh, F. Javier Lopez-Martinez, Wee Kiat New, Hao Xu

TL;DR

This work addresses secure communication in RIS-aided systems featuring fluid antenna systems (FAS) at both the legitimate user and the eavesdropper. The authors derive the CDF and PDF of the SNRs at Bob and Eve using the central limit theorem and a Gaussian copula to account for port correlation, and present a compact SOP expression solved via Gaussian-Laguerre quadrature. They show that increasing the number of RIS elements $M$ and enlarging the fluid antenna dimensions ($N_i$, $W_i$) yield meaningful secrecy gains, reducing the SOP. The results indicate substantial improvements over fixed-antenna baselines, highlighting the practical potential of RIS-aided FAS for secure 6G-like communications, and providing a framework for designing robust physical-layer security in such systems.

Abstract

This paper examines the impact of emerging fluid antenna systems (FAS) on reconfigurable intelligent surface (RIS)-aided secure communications. Specifically, we consider a classic wiretap channel, where a fixed-antenna transmitter sends confidential information to an FAS-equipped legitimate user with the help of an RIS, while an FAS-equipped eavesdropper attempts to decode the message. To evaluate the proposed wireless scenario, we first introduce the cumulative distribution function (CDF) and probability density function (PDF) of the signal-to-noise ratio (SNR) at each node, using the central limit theorem and the Gaussian copula function. We then derive a compact analytical expression for the secrecy outage probability (SOP). Our numerical results reveal how the incorporation of FAS and RIS can significantly enhance the performance of secure communications.

Secrecy Performance Analysis of RIS-Aided Fluid Antenna Systems

TL;DR

This work addresses secure communication in RIS-aided systems featuring fluid antenna systems (FAS) at both the legitimate user and the eavesdropper. The authors derive the CDF and PDF of the SNRs at Bob and Eve using the central limit theorem and a Gaussian copula to account for port correlation, and present a compact SOP expression solved via Gaussian-Laguerre quadrature. They show that increasing the number of RIS elements and enlarging the fluid antenna dimensions (, ) yield meaningful secrecy gains, reducing the SOP. The results indicate substantial improvements over fixed-antenna baselines, highlighting the practical potential of RIS-aided FAS for secure 6G-like communications, and providing a framework for designing robust physical-layer security in such systems.

Abstract

This paper examines the impact of emerging fluid antenna systems (FAS) on reconfigurable intelligent surface (RIS)-aided secure communications. Specifically, we consider a classic wiretap channel, where a fixed-antenna transmitter sends confidential information to an FAS-equipped legitimate user with the help of an RIS, while an FAS-equipped eavesdropper attempts to decode the message. To evaluate the proposed wireless scenario, we first introduce the cumulative distribution function (CDF) and probability density function (PDF) of the signal-to-noise ratio (SNR) at each node, using the central limit theorem and the Gaussian copula function. We then derive a compact analytical expression for the secrecy outage probability (SOP). Our numerical results reveal how the incorporation of FAS and RIS can significantly enhance the performance of secure communications.
Paper Structure (9 sections, 4 theorems, 29 equations, 4 figures)

This paper contains 9 sections, 4 theorems, 29 equations, 4 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. Performance Analysis
  4. Statistical Characterization
  5. Distribution of $\gamma_\mathrm{b}$
  6. Distribution of $\gamma_\mathrm{e}$
  7. SOP Analysis
  8. Numerical Results
  9. Conclusion

Key Result

Proposition 1

The CDF and PDF of $\gamma_\mathrm{b}$ are given by eq-cdf-gb and eq-pdf-gb, respectively, where $\boldsymbol{\mathbf{\varphi}}^{-1}_{A^2}$ is defined in eq-phi (see the top of the next page).

Figures (4)

  • Figure 1: A RIS-aided wiretap channel involving the single fixed-antenna Alice communicating with the FAS-equipped Bob and the FAS-equipped eavesdropper Eve.
  • Figure 2: Analytical CDF and PDF of $\gamma_i$ for different $M$ and selected values of $N_i=4$ and $W_i=1\lambda^2$: (a) CDF of $\gamma_\mathrm{b}$, (b) PDF of $\gamma_\mathrm{b}$, (c) CDF of $\gamma_\mathrm{e}$, and (d) PDF of $\gamma_\mathrm{e}$.
  • Figure 3: (a) SOP versus $\overline{\gamma}_\mathrm{b}$ for different values of $N_\mathrm{b}$ when $M=6$, $N_\mathrm{e}=4$, and $W_\mathrm{e}=1\lambda^2$. (b) SOP versus $\overline{\gamma}_\mathrm{b}$ for different values of $M$ when $N_i=4$ and $W_i=1\lambda^2$.
  • Figure 4: (a) SOP versus $W_\mathrm{b}$ for a fixed $N_\mathrm{b}=16$ and (b) SOP versus $N_\mathrm{b}$ for a fixed $W_\mathrm{b}=1\lambda^2$ for selected values of $\bar{\gamma}_\mathrm{b}$, when $M=6$, $N_\mathrm{e}=4$, and $W_\mathrm{e}=1\lambda^2$.

Theorems & Definitions (7)

  • Proposition 1
  • proof
  • Proposition 2
  • proof
  • Proposition 3
  • proof
  • Lemma 1