Near-Field Wideband Beam Training Based on Distance-Dependent Beam Split

TL;DR

This paper introduces a novel near-field beam training method for 6G XL-MIMO systems that exploits distance-dependent beam split effects to efficiently search both angles and distances simultaneously, reducing training overhead.

Contribution

It reveals the distance-dependent beam split phenomenon and leverages it to develop a beam training method that significantly reduces training overhead by simultaneous angle-distance scanning.

Findings

The proposed method achieves higher beamforming gain.

It reduces training overhead compared to existing methods.

Numerical simulations verify its effectiveness.

Abstract

Near-field beam training is essential for acquiring channel state information in 6G extremely large-scale multiple input multiple output (XL-MIMO) systems. To achieve low-overhead beam training, existing method has been proposed to leverage the near-field beam split effect, which deploys true-time-delay arrays to simultaneously search multiple angles of the entire angular range in a distance ring with a single pilot. However, the method still requires exhaustive search in the distance domain, which limits its efficiency. To address the problem, we propose a distance-dependent beam-split-based beam training method to further reduce the training overheads. Specifically, we first reveal the new phenomenon of distance-dependent beam split, where by manipulating the configurations of time-delay and phase-shift, beams at different frequencies can simultaneously scan the angular domain in multiple distance rings. Leveraging the phenomenon, we propose a near-field beam training method where both different angles and distances can simultaneously be searched in one time slot. Thus, a few pilots are capable of covering the whole angle-distance space for wideband XL-MIMO. Theoretical analysis and numerical simulations are also displayed to verify the superiority of the proposed method on beamforming gain and training overhead.