RIS-Aided Near-Field Localization and Channel Estimation for the Sub-Terahertz System

TL;DR

This paper introduces a near-field localization and channel estimation algorithm for sub-terahertz RIS-assisted systems, addressing the challenges of spherical wavefront propagation in high-frequency near-field scenarios.

Contribution

It proposes a novel NF-JCEL algorithm that decouples user equipment distances and angles, improving localization and channel estimation accuracy in near-field subTHz systems.

Findings

NF-JCEL outperforms conventional far-field algorithms.

Higher resolution accuracy achieved with the proposed method.

Effective decoupling of distances and angles in near-field channels.

Abstract

The low hardware cost makes ultra-large (XL) reconfigurable intelligent surface (RIS) an attractive solution for the performance enhancement of localization and communication systems, but it results in near-field propagation channels, especially for the high-frequency communication systems, e.g. mmWave and sub-terahertz (subTHz) systems. This makes localization and channel estimation in the near field of the RIS-aided subTHz system more challenging. In this paper, we consider the spherical wavefront propagation in the near field of the subTHz system with the assistance of a RIS. A near-field channel estimation and localization (NF-JCEL) algorithm is proposed based on the derived second-order Fresnel approximation of the near-field channel model. To be specific, we first decouple the user equipment (UE) distances and angles of arrival (AoAs) through a down-sampled Toeplitz covariance matrix, so that the vertical and azimuth AoAs in the array steering vectors can be estimated separately with low complexities. Then, the UE distance can be estimated by the simple one-dimensional search, and the channel attenuation coefficients are obtained through the orthogonal matching pursuit (OMP) method. Simulation results validate the superiority of the proposed NF-JCEL algorithm to the conventional far-field algorithm, and show that higher resolution accuracy can be obtained by the proposed algorithm.