Understanding UAV Cellular Communications: From Existing Networks to Massive MIMO

TL;DR

This paper examines UAV cellular communications, comparing current networks with massive MIMO systems, highlighting challenges in UAV cell association, C&C channel support, and the impact on ground users, with practical insights for future deployment.

Contribution

It provides a realistic comparison of existing and next-generation massive MIMO networks for UAVs, emphasizing pilot reuse effects and power control strategies for reliable C&C channels.

Findings

UAV cell association is driven by secondary lobes of base stations.

Massive MIMO can support 100 kbps C&C channels in most cases.

Supporting UAV C&C channels can impact ground user performance due to pilot contamination.

Abstract

The purpose of this article is to bestow the reader with a timely study of UAV cellular communications, bridging the gap between the 3GPP standardization status quo and the more forward-looking research. Special emphasis is placed on the downlink command and control (C&C) channel to aerial users, whose reliability is deemed of paramount technological importance for the commercial success of UAV cellular communications. Through a realistic side-by-side comparison of two network deployments -- a present-day cellular infrastructure versus a next-generation massive MIMO system -- a plurality of key facts are cast light upon, with the three main ones summarized as follows: (i) UAV cell selection is essentially driven by the secondary lobes of a base station's radiation pattern, causing UAVs to associate to far-flung cells; (ii) over a 10 MHz bandwidth, and for UAV heights of up to 300 m, massive MIMO networks can support 100 kbps C&C channels in 74% of the cases when the uplink pilots for channel estimation are reused among base station sites, and in 96% of the cases without pilot reuse across the network; (iii) supporting UAV C&C channels can considerably affect the performance of ground users on account of severe pilot contamination, unless suitable power control policies are in place.