Near-Field Channel Estimation for XL-MIMO: A Deep Generative Model Guided by Side Information

TL;DR

This paper presents a novel near-field channel estimation method for XL-MIMO systems using a deep generative model guided by side information, significantly improving accuracy and efficiency over existing techniques.

Contribution

It introduces a joint AD domain-based physical channel model and a GenAI-guided diffusion approach for refined near-field channel estimation, incorporating side information for enhanced performance.

Findings

Achieves substantial performance gains in channel estimation accuracy.

Enhances sampling efficiency with a non-Markovian GDM.

Demonstrates improved generalization in near-field and far-field regions.

Abstract

This paper investigates the near-field (NF) channel estimation (CE) for extremely large-scale multiple-input multiple-output (XL-MIMO) systems. Considering the pronounced NF effects in XL-MIMO communications, we first establish a joint angle-distance (AD) domain-based spherical-wavefront physical channel model that captures the inherent sparsity of XL-MIMO channels. Leveraging the channel's sparsity in the joint AD domain, the CE is approached as a task of reconstructing sparse signals. Anchored in this framework, we first propose a compressed sensing algorithm to acquire a preliminary channel estimate. Harnessing the powerful implicit prior learning capability of generative artificial intelligence (GenAI), we further propose a GenAI-based approach to refine the estimated channel. Specifically, we introduce the preliminary estimated channel as side information, and derive the evidence lower bound (ELBO) of the log-marginal distribution of the target NF channel conditioned on the preliminary estimated channel, which serves as the optimization objective for the proposed generative diffusion model (GDM). Additionally, we introduce a more generalized version of the GDM, the non-Markovian GDM (NM-GDM), to accelerate the sampling process, achieving an approximately tenfold enhancement in sampling efficiency. Experimental results indicate that the proposed approach is capable of offering substantial performance gain in CE compared to existing benchmark schemes within NF XL-MIMO systems. Furthermore, our approach exhibits enhanced generalization capabilities in both the NF or far-field (FF) regions.