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Secure Beamforming and Reflection Design for RIS-ISAC Systems under Collusion of Passive and Active Eavesdroppers

Tian Zhang, Zhirong Su, Yueyi Dong

TL;DR

This work addresses secure RIS‑aided ISAC in the presence of colluding active and passive eavesdroppers. It formulates a nonconvex secrecy‑rate maximization problem and solves it via an alternating optimization and successive convex approximation framework, yielding the JBRD algorithm that jointly optimizes BS transmit beamforming, RIS reflections, and BS receive filtering under sensing and power constraints. The authors demonstrate convergence and significant secrecy‑rate gains over benchmark schemes, validating the effectiveness of joint beamforming and RIS design for secure ISAC. The results highlight the practical potential of RIS to enhance both security and sensing performance in next‑generation wireless systems.

Abstract

In the paper, the physical-layer security for reconfigurable intelligent surface (RIS) aided integrated sensing and communication (ISAC) system is studied. There is an active eavesdropper (AE) as well as a passive eavesdropper (PE), and they cooperate each other. By joint base station beamforming and RIS reflection design, we aim to achieve the best secure data communications with guaranteed sensing performance. Mathematically, taking the constraints on sensing performance and transmission power in consideration, the system secrecy rate maximization problem is formulated with respect to transmitting beamforming, RIS reflection, and receiving beamforming. The formulated problem is non-convex and is decomposed to three subproblem by applying the alternating optimization scheme. For the decomposed subproblem, we utilize the quadratic penalty method and successive convex approximation (SCA) for the solution derivation. Thereafter, an iterative numerical algorithm, referred to as the joint beamforming and reflection design (JBRD) algorithm, is proposed. Finally, numerical results demonstrate the effectiveness and superiority of the proposed algorithm.

Secure Beamforming and Reflection Design for RIS-ISAC Systems under Collusion of Passive and Active Eavesdroppers

TL;DR

This work addresses secure RIS‑aided ISAC in the presence of colluding active and passive eavesdroppers. It formulates a nonconvex secrecy‑rate maximization problem and solves it via an alternating optimization and successive convex approximation framework, yielding the JBRD algorithm that jointly optimizes BS transmit beamforming, RIS reflections, and BS receive filtering under sensing and power constraints. The authors demonstrate convergence and significant secrecy‑rate gains over benchmark schemes, validating the effectiveness of joint beamforming and RIS design for secure ISAC. The results highlight the practical potential of RIS to enhance both security and sensing performance in next‑generation wireless systems.

Abstract

In the paper, the physical-layer security for reconfigurable intelligent surface (RIS) aided integrated sensing and communication (ISAC) system is studied. There is an active eavesdropper (AE) as well as a passive eavesdropper (PE), and they cooperate each other. By joint base station beamforming and RIS reflection design, we aim to achieve the best secure data communications with guaranteed sensing performance. Mathematically, taking the constraints on sensing performance and transmission power in consideration, the system secrecy rate maximization problem is formulated with respect to transmitting beamforming, RIS reflection, and receiving beamforming. The formulated problem is non-convex and is decomposed to three subproblem by applying the alternating optimization scheme. For the decomposed subproblem, we utilize the quadratic penalty method and successive convex approximation (SCA) for the solution derivation. Thereafter, an iterative numerical algorithm, referred to as the joint beamforming and reflection design (JBRD) algorithm, is proposed. Finally, numerical results demonstrate the effectiveness and superiority of the proposed algorithm.
Paper Structure (13 sections, 1 theorem, 59 equations, 7 figures, 1 table, 1 algorithm)

This paper contains 13 sections, 1 theorem, 59 equations, 7 figures, 1 table, 1 algorithm.

Table of Contents

  1. Introduction
  2. System model
  3. Communications model
  4. Sensing Model
  5. Security Model
  6. Problem formulation
  7. Solution and algorithm design
  8. BS Receive Beamforming Vector Optimization
  9. BS Transmit Beamforming Matrix Optimization
  10. RIS Reflection Coefficient Matrix Optimization
  11. Joint Beamforming and Reflection Optimization Against Colluding Eavesdroppers
  12. Numerical results
  13. Conclusion

Key Result

Lemma 1

(P1) can be rewritten as where with and $m_k = 1 / \sigma_k^2$, with and $m_a = 1 / \sigma_{ae}^2$, with and $m_s = 1 / \sigma_s^2$.

Figures (7)

  • Figure 1: ISAC Dual-Security System for Communication and Sensing
  • Figure 2: Convergence performance of the proposed JBRD algorithm
  • Figure 3: System secrecy rate of JBRD algorithm
  • Figure 4: System secrecy rate performance v.s. $P$
  • Figure 5: System secrecy rate performance v.s. $\gamma_{echo}$
  • ...and 2 more figures

Theorems & Definitions (1)

  • Lemma 1