Joint Beamforming and Port Selection for Fluid Antenna-Assisted Nearshore ISAC Systems

Abstract

Strong three-ray multipath in nearshore environments degrades the performance of conventional fixed-antenna integrated sensing and communication (ISAC) systems. To mitigate spatially dependent fading, we investigate a fluid antenna system (FAS)-assisted nearshore ISAC framework with dynamically reconfigurable discrete ports. A joint beamforming and port selection problem is formulated to maximize the communication sum rate under sensing signal-to-noise ratio (SNR), transmit power, and radio frequency (RF)-chain constraints. The formulated problem is mixed-integer and nonconvex due to coupled binary port selection and continuous beamforming. To solve it efficiently, we develop a block coordinate descent (BCD)-based algorithm. Transmit beamforming is optimized by successive convex approximation (SCA), while port selection is obtained via continuous relaxation and randomized discretization. Simulation results under nearshore three-ray channels demonstrate that the proposed scheme achieves a higher sum rate than fixed-subarray and heuristic selection baselines, while enabling flexible sensing beam control with limited RF-chains.