Two-Stage Joint Angle-Distance Localization for Near-Field Communications

Abstract

Extremely large-scale (XL) antenna arrays and wideband mmWave/THz signaling are expected to enable 6G links with highly directional transmission and near-field beam focusing. In the radiating near-field, the received wavefront is spherical and the array response depends jointly on angle and distance. When combined with wideband operation and a TTD-aided RF architecture, the array response further becomes frequency-dependent across subcarriers, giving rise to a controllable beam-squint effect that can be exploited for localization. However, most existing near-field localization methods rely on sequential angle-distance estimation, which may suffer from error propagation and often require repeated scanning or expensive two-dimensional searches. To address these issues, this paper proposes a beam-squint-assisted joint angle-distance (JAD) localization framework for multi-user near-field wideband systems. Specifically, a coarse-to-fine two-stage estimator is developed, where the coarse stage exploits the frequency-dependent focusing law to obtain an initial JAD estimate from a single scan, and the fine stage performs a localized near-field MUSIC refinement within a small neighborhood of the coarse estimate. In this way, the proposed method preserves high resolution while substantially reducing the search space. Simulation results demonstrate that the proposed method consistently outperforms representative two-step baselines in both angle and range estimation accuracy over a wide SNR range.