Robust Beamforming Optimization for RIS-Assisted THz ISAC Systems

doi:10.1109/TVT.2025.3581890

Robust Beamforming Optimization for RIS-Assisted THz ISAC Systems

2025-06-20

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DOI：10.1109/TVT.2025.3581890

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This paper investigates a reconfigurable intelligent surface (RIS)-assisted terahertz (THz) integrated sensing and communication (ISAC) system. The operation is divided into two stages: a sensing stage to acquire user channel state information (CSI) via received echoes at RIS, and a communication stage to transmit information. Specifically, for the sensing stage, we propose a beam squint-based rapid sensing scheme at RIS with true time delay, and derive the sensing Cramer-Rao bound (CRB) as well as its relationship with CSI error. Next, for the communication stage, we formulate the robust optimization problem of maximizing the transmission capacity by jointly designing RIS reflection coefficients, time delays and sensing time based on obtained imperfect CSI. Since it is difficult to directly solve the formulated problem, we first fix the sensing time, and then propose an alternate optimization scheme to solve RIS reflection coefficients and time delays, where the S-Procedure and semidefinite relaxation (SDR) techniques are applied. Meanwhile, the optimal sensing time is obtained by one dimensional search. Simulation results demonstrate that the proposed scheme achieves superior transmission capacity compared to conventional approaches.

Keywords:

Integrated sensing and communication

terahertz

reconfigurable intelligent surface

beam squint

Cramér-Rao bound

Robust Beamforming Optimization for RIS-Assisted THz ISAC Systems

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