Partially Connected Hybrid Precoder Design for Wideband Near-field Integrated Sensing and Communications

Abstract

Aiming to enhance sensing resolution and improve spectral efficiency, future Integrated Sensing And Communications (ISAC) systems are expected to incorporate extremely large-scale (XL) arrays and large bandwidths centered around high carrier frequencies. This design necessitates considering wideband and near-field effects. In this paper, the design of partially connected hybrid precoders for ISAC is refined and evaluated, focusing on the wideband near-field scenario and addressing monostatic and bistatic co-located Multiple-Input-Multiple-Output (MIMO). For monostatic MIMO, the Cramer-Rao Bound (CRB) for joint Direction-of-Arrival (DOA) and distance estimations of sensing wideband sources is rederived, serving as a performance metric for sensing. For bistatic MIMO, power irradiated at near-field targets is maximized while ensuring that the communication Quality of Service (QoS) for each user is maintained. To address the above nonconvex, high-dimensional problems, a direct alternative minimization, along with an indirect fully digital approximation, is proposed. This method decomposes the original problems into distinct subproblems, enabling effective solutions for each subproblem. Simulation results demonstrate that the proposed wideband near-field ISAC framework can achieve sensing and communication performance close to that of fully digital precoders, given an appropriate communication Signal-to-Noise Ratio (SNR) setting and transmit antenna grouping.