Out-of-Band Distortion in Massive MIMO: What to expect under realistic conditions?

TL;DR

This paper examines the impact of out-of-band distortion in massive MIMO systems under realistic conditions, revealing that traditional models may underestimate OOB emissions and discussing implications for energy efficiency and regulation.

Contribution

It introduces a simulation framework using Ray-Tracing to realistically assess OOB distortion in massive MIMO, challenging the assumptions of i.i.d. Rayleigh fading models.

Findings

i.i.d. Rayleigh models are overly optimistic about OOB emissions.

Realistic multi-path scenarios show higher OOB emissions than predicted.

Implications for regulatory compliance and energy-efficient design are discussed.

Abstract

Massive Multiple Input Multiple Output (MIMO) offers superior capacity for future networks. In the quest for energy efficient implementation of these large array-based trans-mission systems, the power consumption of the Power Amplifiers(PAs) is a main bottleneck. This paper investigates whether it is possible to operate the PAs in their efficient nonlinear region, as the Out-of-Band (OOB) distortion may not get the same array gain as the in-band (IB) signals. We present a framework to simulate the effects under realistic conditions, leveraging on an accurate Ray-Tracing Simulator (RTS). The results show that the often assumed i.i.d. Rayleigh fading channel model results in too optimistic predictions, also in Non Line of Sight (NLoS) multi-path scenarios, regarding the spatial distribution of OOB emissions. We further comment on the consequences in view of current regulatory constraints.