Fading in reflective and heavily shadowed industrial environments with large arrays

TL;DR

This paper investigates how massive MIMO arrays improve reliability in industrial environments with shadowing and reflections by reducing fading effects and channel variations, enabling more robust 5G URLLC applications.

Contribution

It quantifies channel hardening effects in industrial settings and demonstrates how distributed arrays enhance reliability by reducing large-scale power variations.

Findings

Channel hardening reduces small-scale fading variations.

Distributed arrays decrease large-scale power fluctuations.

Massive MIMO approaches i.i.d. Gaussian channel conditions.

Abstract

One of the use cases for 5G systems and beyond is ultra-reliability low-latency communication (URLLC). An enabling technology for URLLC is massive multiple-input multiple-output (MIMO), which can increase reliability due to improved user separation, array gain and the channel hardening effect. Measurements have been performed in an operating factory environment at 3.7 GHz with a co-located massive MIMO array and a unique randomly distributed array. Channel hardening can appear when the number of antennas is increased such that the variations of channel gain (small-scale fading) is decreased and it is here quantified. The cumulative distribution function (CDF) of the channel gains then becomes steeper and its tail is reduced. This CDF is modeled and the required fading margins are quantified. By deploying a distributed array, the large-scale power variations can also be reduced, further improving reliability. The large array in this rich scattering environment, creates a more reliable channel as it approaches an independent identically distributed (i.i.d.) complex Gaussian channel, indicating that one can rethink the system design in terms of e.g. channel coding and re-transmission strategies, in order to reduce latency. To conclude, massive MIMO is a highly interesting technology for reliable connectivity in reflective and heavily shadowed industrial environments.