Beamforming Design for Hierarchical Sensing in Wideband Integrated Sensing and Communications

In this paper, we propose a novel hierarchical sensing framework for integrated sensing and communication systems equipped with uniform planar arrays (UPAs) for wideband scenarios. Leveraging the beam-squint effect inherent in wideband orthogonal frequency-division multiplexing systems, the proposed framework enables efficient two-dimensional angle estimation through a structured multi-stage sensing process. Specifically, the sensing procedure first searches over the elevation angle domain, followed by a dedicated search over the azimuth angle domain given the estimated elevation angles. In each stage, true-time-delay lines and phase shifters of the UPA are jointly configured to simultaneously cover multiple grid points across subcarriers. To enable accurate and efficient target localization, we formulate the angle estimation problem as a sparse signal recovery problem and solve it using conventional compressed sensing algorithms tailored to the hierarchical sensing architecture. Numerical results demonstrate that the proposed framework achieves near-optimal sensing accuracy with significantly reducing sensing time.