Comprehensive Analysis of Behavioral Hardware Impairments in Cell-Free Massive MIMO-OFDM Uplink: Centralized Operation

2025-07-29

AI Summary

This work investigates the impact of hardware impairments—namely, nonlinear distortion, phase noise, IQ imbalance, and low-resolution analog-to-digital converters (ADCs)—introduced by low-cost access points (APs) on the spectral efficiency of uplink cell-free massive MIMO-OFDM systems. It presents the first joint modeling and analysis of these impairments in broadband settings. Method: A distortion-aware combining vector design is proposed, leveraging Bussgang decomposition to uniformly model all hardware impairments as colored noise. Under a centralized signal processing architecture, channel state information (CSI) is shared across APs, enabling joint signal combining. Contribution/Results: Compared to conventional distortion-agnostic designs, the proposed approach significantly improves uplink spectral efficiency. It demonstrates the feasibility and robustness of cell-free massive MIMO under practical hardware constraints, providing both theoretical foundations and a practical receiver design paradigm for cost-effective deployment.

Technology Category

• Machine Learning: Hardware-aware ML
• Cognitive Modeling & Cognitive Systems: Applications
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• Security and Privacy: Large-scale security measurements

Abstract

Cell-free massive MIMO is a key 6G technology, offering superior spectral and energy efficiency. However, its dense deployment of low-cost access points (APs) makes hardware impairments unavoidable. While narrowband impairments are well-studied, their impact in wideband systems remains unexplored. This paper provides the first comprehensive analysis of hardware impairments, such as nonlinear distortion in low-noise amplifiers, phase noise, in-phase-quadrature imbalance, and low-resolution analog-to-digital converters, on uplink spectral efficiency in cell-free massive MIMO. Using an OFDM waveform and centralized processing, APs share channel state information for joint uplink combining. Leveraging Bussgang decomposition, we derive a distortion-aware combining vector that optimizes spectral efficiency by modeling distortion as independent colored noise.

Problem

• Analyze hardware impairments in cell-free massive MIMO-OFDM uplink
• Study impact of wideband impairments on spectral efficiency
• Develop distortion-aware combining for optimized uplink performance

Innovation

• Centralized processing for joint uplink combining
• Bussgang decomposition for distortion-aware combining
• Modeling distortion as independent colored noise