A Novel Near-Field Dictionary Design for Hybrid MIMO with Uniform Planar Arrays

TL;DR

This paper introduces a specialized near-field dictionary grid design for hybrid U-MIMO systems with planar arrays, improving channel estimation accuracy and spectral efficiency when users are near a reference plane.

Contribution

A new near-field grid design tailored for ground-level user scenarios, incorporating a channel accuracy metric to enhance codebook performance.

Findings

Proposed grid outperforms existing designs in accuracy and spectral efficiency.

Performance gains are significant when users are close to the reference plane.

Traditional far-field sampling is less effective in near-field conditions.

Abstract

Near-field ultra-massive MIMO (U-MIMO) systems provide enhanced spatial resolution but present challenges for channel estimation, particularly when hybrid architectures are employed. Within this framework, dictionary-based channel estimation schemes are needed to achieve accurate reconstruction from a reduced set of measurements. However, existing near-field dictionaries generally provide full three-dimensional coverage, which is unnecessary when user equipments are primarily located on the ground. In this paper, we propose a novel near-field grid design tailored to this common scenario. Specifically, grid points lie on a reference plane located at an arbitrary height with respect to the U-MIMO system, equipped with a uniform planar array. Furthermore, a channel accuracy metric is used to improve codebook performance, and to remark the limitations of the traditional far-field angular sampling in the near field. Results show that, as long as user equipments are not far from the reference plane, the proposed grid outperforms state-of-the-art designs in both channel estimation accuracy and spectral efficiency.