Worst-case secrecy rate maximization for near-field secure integrated sensing and communication with hybrid reconfigurable intelligent surfaces

Abstract

This work investigates physical-layer security design for near-field integrated sensing and communication systems assisted by a hybrid reconfigurable intelligent surface (H-RIS). The H-RIS supports both signal reflection and sensing-echo reception, enabling secure cascaded transmission and local echo measurement. A worst-case secrecy rate maximization problem is formulated by jointly optimizing BS beamforming, artificial noise covariance, and H-RIS reflection phases under transmit-power, sensing, and hardware constraints. An alternating optimization algorithm combining fractional programming, successive convex approximation, and penalty-based relaxation is developed. Simulation results show that the proposed scheme achieves higher WCSR than benchmark schemes and improves security performance under different system configurations.