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STAR-RIS Enabled ISAC Systems: Joint Rate Splitting and Beamforming Optimization

Yuan Liu, Ruichen Zhang, Ruihong Jiang, Yongdong Zhu, Huimin Hu, Qiang Ni, Zesong Fei, Dusit Niyato

Abstract

This paper delves into an integrated sensing and communication (ISAC) system bolstered by a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS). Within this system, a base station (BS) is equipped with communication and radar capabilities, enabling it to communicate with ground terminals (GTs) and concurrently probe for echo signals from a target of interest. Moreover, to manage interference and improve communication quality, the rate splitting multiple access (RSMA) scheme is incorporated into the system. The signal-to-interference-plus-noise ratio (SINR) of the received sensing echo signals is a measure of sensing performance. We formulate a joint optimization problem of common rates, transmit beamforming at the BS, and passive beamforming vectors of the STAR-RIS. The objective is to maximize sensing SINR while guaranteeing the communication rate requirements for each GT. We present an iterative algorithm to address the non-convex problem by invoking Dinkelbach's transform, semidefinite relaxation (SDR), majorization-minimization, and sequential rank-one constraint relaxation (SROCR) theories. Simulation results manifest that the performance of the studied ISAC network enhanced by the STAR-RIS and RSMA surpasses other benchmarks considerably. The results evidently indicate the superior performance improvement of the ISAC system with the proposed RSMA-based transmission strategy design and the dynamic optimization of both transmission and reflection beamforming at STAR-RIS.

STAR-RIS Enabled ISAC Systems: Joint Rate Splitting and Beamforming Optimization

Abstract

This paper delves into an integrated sensing and communication (ISAC) system bolstered by a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS). Within this system, a base station (BS) is equipped with communication and radar capabilities, enabling it to communicate with ground terminals (GTs) and concurrently probe for echo signals from a target of interest. Moreover, to manage interference and improve communication quality, the rate splitting multiple access (RSMA) scheme is incorporated into the system. The signal-to-interference-plus-noise ratio (SINR) of the received sensing echo signals is a measure of sensing performance. We formulate a joint optimization problem of common rates, transmit beamforming at the BS, and passive beamforming vectors of the STAR-RIS. The objective is to maximize sensing SINR while guaranteeing the communication rate requirements for each GT. We present an iterative algorithm to address the non-convex problem by invoking Dinkelbach's transform, semidefinite relaxation (SDR), majorization-minimization, and sequential rank-one constraint relaxation (SROCR) theories. Simulation results manifest that the performance of the studied ISAC network enhanced by the STAR-RIS and RSMA surpasses other benchmarks considerably. The results evidently indicate the superior performance improvement of the ISAC system with the proposed RSMA-based transmission strategy design and the dynamic optimization of both transmission and reflection beamforming at STAR-RIS.

Paper Structure

This paper contains 19 sections, 1 theorem, 42 equations, 9 figures, 2 tables, 3 algorithms.

Table of Contents

  1. Introduction
  2. Background
  3. Related Work
  4. Motivation and Contributions
  5. system model
  6. Network Model
  7. Transmission Model
  8. Sensing Model
  9. Problem formulation and proposed solution
  10. Problem Formulation
  11. Proposed Algorithm
  12. Complexity analysis of proposed algorithm
  13. Convergence Analysis
  14. Numerical results and analysis
  15. Simulation Settings
  16. ...and 4 more sections

Key Result

Theorem 1

If the optimized beamforming vectors for sub-problem ${\mathbf {P}}_{\textbf{B1}}$ is denoted as $\{\widehat{{\bf W}}_c, \widehat{{\bf W}}_{p,k}, \widehat{{\bf W}}_0\}$, there always exists another set of solutions $\{\overline{{\bf W}}_c,\overline{{\bf W}}_{p,k}, \overline{{\bf W}}_{0}\}$. It can a

Figures (9)

  • Figure 1: STAR-RIS empowered downlink ISAC system with RSMA scheme.
  • Figure 2: Flowchart of the proposed algorithm.
  • Figure 3: Convergence performances under different rate thresholds and transmit powers.
  • Figure 4: Sensing SINR versus transmit power with different system designs.
  • Figure 5: Sensing SINR versus the number of STAR-RIS elements $M$ with different system designs.
  • ...and 4 more figures

Theorems & Definitions (1)

  • Theorem 1