Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

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

Luca Antonelli, Antonio Alberto D Amico, Luca Sanguinetti

TL;DR

A novel near-field grid design tailored to the U-MIMO system, equipped with a uniform planar array, which outperforms state-of-the-art designs in both channel estimation accuracy and spectral efficiency.

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.

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

TL;DR

A novel near-field grid design tailored to the U-MIMO system, equipped with a uniform planar array, which outperforms state-of-the-art designs in both channel estimation accuracy and spectral efficiency.

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.
Paper Structure (20 sections, 1 theorem, 56 equations, 15 figures, 1 table, 1 algorithm)

This paper contains 20 sections, 1 theorem, 56 equations, 15 figures, 1 table, 1 algorithm.

Table of Contents

  1. Introduction
  2. Literature review
  3. Contributions
  4. Organization and Notation
  5. System Model
  6. Channel estimation
  7. Dictionary-based channel estimation
  8. Review of far-field dictionary design
  9. Channel Estimation Accuracy
  10. Case A ($N_{\rm{RF}}\tau > M$)
  11. Case B ($N_{\rm{RF}}\tau < M$)
  12. Proposed near-field grid design
  13. Level Curves
  14. RP-Circles
  15. Grid construction
  16. ...and 5 more sections

Key Result

Lemma 1

Consider an arbitrary point on the RP given by $\boldsymbol{\mathbf{x}} = (\rho\cos{\varphi},\rho\sin{\varphi},-b)$ and denote with $R$ the distance from the point $\boldsymbol{\mathbf{x}}$ to the center of the UPA. Then, define the Fresnel distanceselvan2017fraunhofer as $R_F= 0.5\sqrt{\frac{L^3}{\ which is commonly referred to as the Fresnel (or parabolic) approximation10070575.

Figures (15)

  • Figure 1: Pictorial illustration of our system model.
  • Figure 2: Traditional far-field dictionary directions with $\lambda$ = $1$ cm, $M_H = 101$, $M_V = 11$ and $\delta_H = \delta_V = \lambda/2$.
  • Figure 3: Average NMSE of channel estimates as a function of the distance $R$. The number of observations is $N_{\rm{RF}}\tau = \{5000,500\}$ in scenarios A and B, respectively.
  • Figure 4: $\mathcal{L}$-curves $\Gamma(R,\varphi)$ for different constant values and $b = 0$ or $20$ m.
  • Figure 5: Angular correlation of the steering vectors of two grid points on adjacent $\mathcal{L}$-curves at same distance $R$ from the BS.
  • ...and 10 more figures

Theorems & Definitions (1)

  • Lemma 1: Fresnel approximation