Hybrid Beamforming for ISAC Systems With Reconfigurable Subarray Architecture

In this work, we propose a reconfigurable subarray (RS) architecture for a millimeter-wave (mmWave) integrated sensing and communication (ISAC) system to improve itsintegration gain and cost-effectiveness. The RS-based hybrid beamforming (HBF) is optimized to maximize the sum-rate of the communication system while ensuring the sensing signal-to-clutter-plus-noise ratio (SCNR) requirement. The critical idea in solving the above non-convex coupling problem is that we transform the sum-rate maximizationproblem to an equivalent weighted minimum mean square error problem, then penalty dual decomposition (PDD) is applied to decouple the analog and digital beamformers and optimize the HBF in an alternating manner. Simulations corroborate that, with the RS architecture and HBF, ISAC offers effective communication and sensing performance and optimal energy efficiency (EE) compared to other hybrid architectures.