Distributed Two-Phase Processing for Modular XL-MIMO with Wireless Fronthaul under Hardware Impairments

2026-05-22

AI Summary

This work addresses the limitations in spectral efficiency of modular cell-free massive MIMO systems under wireless fronthaul, which are exacerbated by hardware impairments. To tackle this challenge, the paper proposes a distributed two-stage processing framework that jointly optimizes user transmit powers and fronthaul amplification coefficients under amplify-and-forward fronthaul constraints and practical hardware limitations. The authors innovatively develop a unified distortion model encompassing impairments at both the access and fronthaul segments, and design a distortion-aware receiver based on the weighted minimum mean square error (WMMSE) criterion to enable joint optimization of power control and signal processing. Compared to fixed strategies, the proposed method significantly enhances uplink spectral efficiency—particularly when the central processing unit is equipped with a moderate number of antennas—and provides quantitative insights into the relative impacts of the two types of hardware impairments.

Abstract

Modular extremely large-scale MIMO (XL-MIMO) architectures combined with wireless fronthaul provide a scalable alternative to monolithic arrays, but their performance is sensitive to hardware impairments and resource allocation strategies. In this paper, we consider a distributed two-phase processing framework for modular XL-MIMO systems employing amplify-and-forward wireless fronthaul under practical hardware constraints. We jointly model access-side and fronthaul-side distortions and formulate a weighted minimum mean-square error (WMMSE)-based optimization problem that maximizes the uplink sum spectral efficiency (SE) by jointly adjusting UE transmit powers and fronthaul amplification levels. The resulting algorithm alternates between distortion-aware receiver design and convex power-control updates. Numerical results demonstrate that the proposed joint optimization significantly improves spectral efficiency compared to fixed transmission strategies, particularly when the CPU has a moderate number of antennas, while also quantifying the relative impact of access and fronthaul impairments.

Problem

• Modular XL-MIMO
• Wireless Fronthaul
• Hardware Impairments
• Spectral Efficiency
• Distributed Processing

Innovation

• modular XL-MIMO
• wireless fronthaul
• hardware impairments
• WMMSE optimization
• distributed two-phase processing