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Secure SWIPT in the Multiuser STAR-RIS Aided MISO Rate Splitting Downlink

Hamid Reza Hashempour, Hamed Bastami, Majid Moradikia, Seyed A. Zekavat, Hamid Behroozi, Gilberto Berardinelli, A. Lee Swindlehurst

TL;DR

This work addresses secure SWIPT in a downlink MISO network aided by STAR-RIS using Rate-Splitting Multiple Access. It develops a robust design that jointly optimizes active beamforming at the BS and passive transmission/reflection beamforming at the STAR-RIS under imperfect CSI for UERs, formulating a worst-case WCSSR objective. A two-step SPCA-based algorithm alternates between precoder optimization and STAR-RIS beamforming, with initialization to ensure feasibility and convergence to KKT points; simulations show significant gains in secrecy rate and spectral efficiency over OMA and NOMA, with robustness to CSI imperfections and benefits from larger STAR-RIS size. The findings highlight the practical potential of combining RSMA with STAR-RIS for secure SWIPT in next-generation networks, and point to future work on quantized RIS, nonlinear EH models, and theoretical performance bounds.

Abstract

Recently, simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) have emerged as a novel technology that provides 360 coverage and new degrees-of-freedom (DoFs). They are also capable of manipulating signal propagation and simultaneous wireless information and power transfer (SWIPT). This paper introduces a novel STAR-RIS-aided secure SWIPT system for downlink multiple input single output rate-splitting multiple access (RSMA) networks. The transmitter concurrently communicates with the information receivers (IRs) and sends energy to untrusted energy receivers (UERs). The UERs are also capable of wiretapping the IR streams. We assume that the channel state information (CSI) of the IRs is known at the information transmitter, but only imperfect CSI for the UERs is available at the energy transmitter. By exploiting RSMA, the base station splits the messages of the IRs into common and private parts. The former is encoded into a common stream that can be decoded by all IRs, while the private messages are individually decoded by their respective IRs. We find the precoders and STAR-RIS configuration that maximizes the achievable worst-case sum secrecy rate of the IRs under a total transmit power constraint, a sum energy constraint for the UERs, and subject to constraints on the transmission and reflection coefficients. The formulated problem is non-convex and has intricately coupled variables. To tackle this challenge, a suboptimal two-step iterative algorithm based on the sequential parametric convex approximation method is proposed. Simulations demonstrate that the RSMA-based algorithm implemented with a STAR-RIS enhances both the rate of confidential information transmission and the total spectral efficiency. Furthermore, our method surpasses the performance of both orthogonal multiple access (OMA) and non-OMA (NOMA).

Secure SWIPT in the Multiuser STAR-RIS Aided MISO Rate Splitting Downlink

TL;DR

This work addresses secure SWIPT in a downlink MISO network aided by STAR-RIS using Rate-Splitting Multiple Access. It develops a robust design that jointly optimizes active beamforming at the BS and passive transmission/reflection beamforming at the STAR-RIS under imperfect CSI for UERs, formulating a worst-case WCSSR objective. A two-step SPCA-based algorithm alternates between precoder optimization and STAR-RIS beamforming, with initialization to ensure feasibility and convergence to KKT points; simulations show significant gains in secrecy rate and spectral efficiency over OMA and NOMA, with robustness to CSI imperfections and benefits from larger STAR-RIS size. The findings highlight the practical potential of combining RSMA with STAR-RIS for secure SWIPT in next-generation networks, and point to future work on quantized RIS, nonlinear EH models, and theoretical performance bounds.

Abstract

Recently, simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) have emerged as a novel technology that provides 360 coverage and new degrees-of-freedom (DoFs). They are also capable of manipulating signal propagation and simultaneous wireless information and power transfer (SWIPT). This paper introduces a novel STAR-RIS-aided secure SWIPT system for downlink multiple input single output rate-splitting multiple access (RSMA) networks. The transmitter concurrently communicates with the information receivers (IRs) and sends energy to untrusted energy receivers (UERs). The UERs are also capable of wiretapping the IR streams. We assume that the channel state information (CSI) of the IRs is known at the information transmitter, but only imperfect CSI for the UERs is available at the energy transmitter. By exploiting RSMA, the base station splits the messages of the IRs into common and private parts. The former is encoded into a common stream that can be decoded by all IRs, while the private messages are individually decoded by their respective IRs. We find the precoders and STAR-RIS configuration that maximizes the achievable worst-case sum secrecy rate of the IRs under a total transmit power constraint, a sum energy constraint for the UERs, and subject to constraints on the transmission and reflection coefficients. The formulated problem is non-convex and has intricately coupled variables. To tackle this challenge, a suboptimal two-step iterative algorithm based on the sequential parametric convex approximation method is proposed. Simulations demonstrate that the RSMA-based algorithm implemented with a STAR-RIS enhances both the rate of confidential information transmission and the total spectral efficiency. Furthermore, our method surpasses the performance of both orthogonal multiple access (OMA) and non-OMA (NOMA).
Paper Structure (27 sections, 10 theorems, 53 equations, 10 figures, 4 tables, 4 algorithms)

This paper contains 27 sections, 10 theorems, 53 equations, 10 figures, 4 tables, 4 algorithms.

Table of Contents

  1. Introduction
  2. Related Works
  3. Studies on STAR-RIS Assisted Networks
  4. Studies on Secure RIS-Aided SWIPT
  5. Motivations and Contributions
  6. Organization and Notation
  7. System Model and Preliminaries
  8. Assumptions and Justification
  9. STAR-RIS Signal Model
  10. System Model
  11. Proposed WCSSR Maximization
  12. Problem Formulation
  13. SPCA-based Solution for Precoder Optimization
  14. Non-Convex Objective Function \ref{['P1-a']}
  15. Non-convex constraint \ref{['P1-d']}
  16. ...and 12 more sections

Key Result

Proposition 1

An affine approximation of constraint P3-c, $\forall j \in \mathcal{J}$ is given by: where

Figures (10)

  • Figure 1: Illustration of signal propagation of STAR-RISs Joint design
  • Figure 2: System model
  • Figure 3: Analyzing the problem: A step-by-step overview
  • Figure 4: Simulation scenario for the STAR-RIS-RSMA system.
  • Figure 5: Convergence behavior of Algorithm \ref{['Alg1']} versus the number of iterations for different values of transmit power when $N_T = 4$, and $M=10$.
  • ...and 5 more figures

Theorems & Definitions (20)

  • Proposition 1
  • proof
  • Proposition 2
  • proof
  • Proposition 3
  • proof
  • Proposition 4
  • proof
  • Proposition 5
  • proof
  • ...and 10 more