Spectral and Energy Efficiency of Cell-Free Massive MIMO Systems with Hardware Impairments

TL;DR

This paper investigates how hardware impairments affect cell-free massive MIMO systems, deriving formulas for spectral and energy efficiency, and demonstrating the system's resilience to hardware imperfections as the number of access points increases.

Contribution

It provides the first analytical study of hardware impairments in cell-free massive MIMO, including new closed-form efficiency expressions and a hardware-quality scaling law.

Findings

Hardware impairments' impact diminishes with more APs.

Cell-free massive MIMO is resilient to hardware impairments.

Derived closed-form expressions for efficiency metrics.

Abstract

Cell-free massive multiple-input multiple-output (MIMO), with a large number of distributed access points (APs) that jointly serve the user equipments (UEs), is a promising network architecture for future wireless communications. To reduce the cost and power consumption of such systems, it is important to utilize low-quality transceiver hardware at the APs. However, the impact of hardware impairments on cell-free massive MIMO has thus far not been studied. In this paper, we take a first look at this important topic by utilizing well-established models of hardware distortion and deriving new closed-form expressions for the spectral and energy efficiency. These expressions provide important insights into the practical impact of hardware impairments and also how to efficiently deploy cell-free systems. Furthermore, a novel hardware-quality scaling law is presented. It proves that the impact of hardware impairments at the APs vanish as the number of APs grows. Numerical results validate that cell-free massive MIMO systems are inherently resilient to hardware impairments.