Beampattern Gain Optimization for Near-Field Wideband Multi-User ISAC Systems

Abstract

With the help of large-scale antenna arrays and sufficient bandwidth, integrated sensing and communication (ISAC) system can provide high-rate communications and high-accuracy target sensing. However, such ISAC system may experience near-field propagation and severe beam squint effects, which makes the beamforming design challenging. To solve this problem, a near-field wideband ISAC system is investigated in this paper, which serves multiple communication users and sense one target simultaneously. To mitigate the adverse effect of beam squint, a phase-shifter (PS) and true-time-delay (TTD) architecture is adopted, which can construct a frequency-dependent analog beamformer. Then, an ISAC beamforming optimization problem is formulated to maximize the sensing beampattern gain while satisfying the communication SINR constraints. To handle the strong coupling among optimization variables, a penalty-based block coordinate descent (BCD) algorithm is developed. In particular, the auxiliary precoder is updated via successive convex approximation (SCA), and the PS-TTD analog beamformer is optimized through an ADMM-based method. Numerical results demonstrate that the proposed scheme effectively mitigates beam squint and achieves improved sensing beampattern performance while satisfying the communication QoS requirements.