Near-Field Integrated Sensing and Communication for Multi-Target Indication

TL;DR

This paper introduces a unified near-field ISAC beamforming framework that jointly supports multi-user communication and multi-target sensing by exploiting spherical-wave propagation, enabling high-resolution detection and high-rate data transmission.

Contribution

It proposes a novel joint beamforming design for near-field ISAC that maximizes sensing accuracy while ensuring communication performance, extending classical measures to near-field scenarios.

Findings

Achieves simultaneous multi-target resolution and communication in near-field conditions.

Outperforms far-field and single-target benchmarks in simulations.

Provides an efficient semidefinite relaxation and closed-form solution for beamforming.

Abstract

Integrated sensing and communication (ISAC) in the near-field regime offers the potential to jointly support high-rate downlink transmission and high-resolution multi-target detection by exploiting the spherical-wave nature of electromagnetic propagation. In this paper, we propose a unified beamforming framework for a multi-user multi-target near-field ISAC system. In this system, a multi-antenna base station simultaneously serves multiple single-antenna users and senses multiple point-targets without prior knowledge of their radar cross sections. By optimizing the transmit covariance matrix, our design maximizes the minimum weighted transmit beampattern gain across all targets to ensure accurate sensing while strictly limiting inter-target cross-correlations and guaranteeing per-user communication rate and total power constraints. We extend classical far-field beampattern and cross-correlation measures to the near-field by incorporating both angle and range dependencies, enabling discrimination of targets along the same direction but at different distances. The resulting non-convex program is efficiently relaxed to a semidefinite program via rank-one lifting. We then develop a closed-form reconstruction to recover optimal rank-one beamformers. Numerical simulations demonstrate that our near-field ISAC design can simultaneously resolve and serve users/targets along the same direction but at different distances, achieving significant gains over far-field and single-target benchmarks.