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STAR-RIS Aided Secure MIMO Communication Systems

Xiequn Dong, Zesong Fei, Xinyi Wang, Meng Hua, Qingqing Wu

TL;DR

This work tackles secrecy-rate optimization in STAR-RIS aided secure MIMO systems by jointly designing BS active beamforming and STAR-RIS passive beamforming under energy-splitting operation. An alternating optimization framework leverages MMSE reformulation for the active-beamforming subproblem and Majorization-Minimization for the RIS phase updates, with amplitudes handled via convex QCQPs. The approach yields closed-form phase updates and competitive, scalable performance, outperforming benchmark schemes as the RIS size and transmit power increase. The results highlight the practical potential of STAR-RIS to enhance physical-layer security in future wireless networks.

Abstract

This paper investigates simultaneous transmission and reflection reconfigurable intelligent surface (STAR-RIS) aided physical layer security (PLS) in multiple-input multiple-output (MIMO) systems, where the base station (BS) transmits secrecy information with the aid of STAR-RIS against multiple eavesdroppers equipped with multiple antennas. We aim to maximize the secrecy rate by jointly optimizing the active beamforming at the BS and passive beamforming at the STAR-RIS, subject to the hardware constraint for STAR-RIS. To handle the coupling variables, a minimum mean-square error (MMSE) based alternating optimization (AO) algorithm is applied. In particular, the amplitudes and phases of STAR-RIS are divided into two blocks to simplify the algorithm design. Besides, by applying the Majorization-Minimization (MM) method, we derive a closed-form expression of the STAR-RIS's phase shifts. Numerical results show that the proposed scheme significantly outperforms various benchmark schemes, especially as the number of STAR-RIS elements increases.

STAR-RIS Aided Secure MIMO Communication Systems

TL;DR

This work tackles secrecy-rate optimization in STAR-RIS aided secure MIMO systems by jointly designing BS active beamforming and STAR-RIS passive beamforming under energy-splitting operation. An alternating optimization framework leverages MMSE reformulation for the active-beamforming subproblem and Majorization-Minimization for the RIS phase updates, with amplitudes handled via convex QCQPs. The approach yields closed-form phase updates and competitive, scalable performance, outperforming benchmark schemes as the RIS size and transmit power increase. The results highlight the practical potential of STAR-RIS to enhance physical-layer security in future wireless networks.

Abstract

This paper investigates simultaneous transmission and reflection reconfigurable intelligent surface (STAR-RIS) aided physical layer security (PLS) in multiple-input multiple-output (MIMO) systems, where the base station (BS) transmits secrecy information with the aid of STAR-RIS against multiple eavesdroppers equipped with multiple antennas. We aim to maximize the secrecy rate by jointly optimizing the active beamforming at the BS and passive beamforming at the STAR-RIS, subject to the hardware constraint for STAR-RIS. To handle the coupling variables, a minimum mean-square error (MMSE) based alternating optimization (AO) algorithm is applied. In particular, the amplitudes and phases of STAR-RIS are divided into two blocks to simplify the algorithm design. Besides, by applying the Majorization-Minimization (MM) method, we derive a closed-form expression of the STAR-RIS's phase shifts. Numerical results show that the proposed scheme significantly outperforms various benchmark schemes, especially as the number of STAR-RIS elements increases.
Paper Structure (8 sections, 1 theorem, 32 equations, 4 figures, 1 algorithm)

This paper contains 8 sections, 1 theorem, 32 equations, 4 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model and Problem Formulation
  3. Proposed Algorithm
  4. MMSE-based Beamforming Optimization Algorithm
  5. MM-based Algorithm
  6. Overall Algorithm and Complexity Analysis
  7. Numerical results
  8. Conclusion

Key Result

Lemma 1

According to 9279253, the upper-bounded function $g( {\left. {{\pmb\theta _k}} \right|{{\pmb{\tilde{\theta}} }_k}} )$ for $g\left( {{\pmb\theta _k}} \right)$ can be expressed as where $\lambda_{\max}$ is the maximum eigenvalue of $\pmb\Gamma_k$.

Figures (4)

  • Figure 1: An illustration of the STAR-RIS-aided secure MIMO communication system.
  • Figure 2: Convergence of the proposed algorithm.
  • Figure 3: Secrecy rate versus the transmit power of BS.
  • Figure 4: Secrecy rate versus the number of STAR-RIS elements.

Theorems & Definitions (1)

  • Lemma 1