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Hybrid STAR-RIS Enabled Integrated Sensing and Communication

Zehra Yigit, Ertugrul Basar

TL;DR

The paper addresses multi-user, multi-target ISAC with full-space coverage by deploying a dual-sided hybrid STAR-RIS that combines passive reflective elements with active transmissive elements. It develops an SDR-based optimization framework to jointly optimize STAR-RIS coefficients and BS beamforming to maximize the minimum target SINR under communication constraints, and derives the CRB for 2D AoD estimation to evaluate sensing accuracy. Results show that the hybrid STAR-RIS substantially improves sensing SINR and AoD estimation relative to passive RIS benchmarks, while highlighting a trade-off between the amplification level, RIS power consumption, and overall system performance. The work provides a practical methodology for designing energy-aware STAR-RIS-assisted ISAC systems with balanced sensing and communication capabilities across full space, supported by analytical bounds and extensive simulations.

Abstract

Integrated sensing and communication (ISAC) is recognized as one of the key enabling technologies for sixth-generation (6G) wireless communication networks, facilitating diverse emerging applications and services in an energy and cost-efficient manner. This paper proposes a multi-user multi-target ISAC system to enable full-space coverage for communication and sensing tasks. The proposed system employs a hybrid simultaneous transmission and reflection reconfigurable intelligent surface (STAR-RIS) comprising active transmissive and passive reflective elements. In the proposed scheme, the passive reflective elements support communication and sensing links for local communication users and sensing targets situated within the same physical region as the base station (BS), while low-power active transmissive elements are deployed to improve sensing performance and overcome high path attenuation due to multi-hop transmission for distant communication users and sensing targets situated far from of the coverage area of the BS. Moreover, to optimize the transmissive/reflective coefficients of the hybrid STAR-RIS, a semi-definite relaxation (SDR)-based algorithm is proposed. Furthermore, to evaluate communication and sensing performance, signal-to-interference-noise ratio (SINR) and Cramer-Rao bound (CRB) metrics have been derived and investigated via conducting extensive computer simulations.

Hybrid STAR-RIS Enabled Integrated Sensing and Communication

TL;DR

The paper addresses multi-user, multi-target ISAC with full-space coverage by deploying a dual-sided hybrid STAR-RIS that combines passive reflective elements with active transmissive elements. It develops an SDR-based optimization framework to jointly optimize STAR-RIS coefficients and BS beamforming to maximize the minimum target SINR under communication constraints, and derives the CRB for 2D AoD estimation to evaluate sensing accuracy. Results show that the hybrid STAR-RIS substantially improves sensing SINR and AoD estimation relative to passive RIS benchmarks, while highlighting a trade-off between the amplification level, RIS power consumption, and overall system performance. The work provides a practical methodology for designing energy-aware STAR-RIS-assisted ISAC systems with balanced sensing and communication capabilities across full space, supported by analytical bounds and extensive simulations.

Abstract

Integrated sensing and communication (ISAC) is recognized as one of the key enabling technologies for sixth-generation (6G) wireless communication networks, facilitating diverse emerging applications and services in an energy and cost-efficient manner. This paper proposes a multi-user multi-target ISAC system to enable full-space coverage for communication and sensing tasks. The proposed system employs a hybrid simultaneous transmission and reflection reconfigurable intelligent surface (STAR-RIS) comprising active transmissive and passive reflective elements. In the proposed scheme, the passive reflective elements support communication and sensing links for local communication users and sensing targets situated within the same physical region as the base station (BS), while low-power active transmissive elements are deployed to improve sensing performance and overcome high path attenuation due to multi-hop transmission for distant communication users and sensing targets situated far from of the coverage area of the BS. Moreover, to optimize the transmissive/reflective coefficients of the hybrid STAR-RIS, a semi-definite relaxation (SDR)-based algorithm is proposed. Furthermore, to evaluate communication and sensing performance, signal-to-interference-noise ratio (SINR) and Cramer-Rao bound (CRB) metrics have been derived and investigated via conducting extensive computer simulations.
Paper Structure (15 sections, 43 equations, 9 figures, 1 table)

This paper contains 15 sections, 43 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. Prior Works
  3. Motivation and Contributions
  4. Organization
  5. System Model
  6. Hybrid STAR-RIS-Enabled ISAC
  7. Communication Model
  8. Sensing Model
  9. Performance Metrics and Problem Formulation
  10. Target SINR Analysis
  11. User SINR Analysis
  12. Problem Formulation
  13. Cramer-Rao Bound (CRB) Analysis
  14. Simulation Results
  15. Conclusion

Figures (9)

  • Figure 1: System model of hybrid RIS-assisted ISAC.
  • Figure 2: A generic signal model of the hybrid STAR-RIS.
  • Figure 3: SINR of target O$_T$ versus power consumption at active STAR-RIS elements for $N=36$ and different $P_{\text{BS}}$ values.
  • Figure 4: SINR of target $O_T$ for varying $P_\mathrm{RIS}$ (a) and $P_\mathrm{BS}$ (b).
  • Figure 5: SINR of the targets O$_R$ and O$_T$ for varying numbers of STAR-RIS elements $N$.
  • ...and 4 more figures