Joint DFBS Beamforming and HRIS Beamforming for HRIS-Aided ISAC Systems

The hybrid reconfigurable intelligent surface (HRIS) is capable of simultaneous programmable reflections and sensing. It has been applied in the fields of either communication or target localization, but its potential in integrated sensing and communication (ISAC) systems has yet to be fully discussed. In this paper, we consider an HRIS-aided ISAC system, where a dual-function base station (DFBS) simultaneously transmits communication and radar signals with the aid of an HRIS, and the HRIS not only facilitates the transmission of communication signals to users but also receives radar signals reflected by the target. Under such a scenario, an optimization problem is formulated to maximize the sensing signal-to-interference-plus-noise ratio (SINR) while satisfying the communication SINR requirements, the transmit power budget of the DFBS and the unit modulus property of the reflection and reception coefficients. Subsequently, we propose an efficient iterative algorithm based on the Rayleigh quotient, the Dinkelbach's transform, and the successive convex approximation (SCA) methods to solve the formulated problem. Simulation results illustrate that the HRIS with equal amplitude factors and just optimizing its phase shifts can also improve the sensing SINR while guaranteeing the communication SINR requirements.