What Will the Future of UAV Cellular Communications Be? A Flight from 5G to 6G

Abstract

What will the future of UAV cellular communications be? In this tutorial article, we address such a compelling yet difficult question by embarking on a journey from 5G to 6G and sharing a large number of realistic case studies supported by original results. We start by overviewing the status quo on UAV communications from an industrial standpoint, providing fresh updates from the 3GPP and detailing new 5G NR features in support of aerial devices. We then show the potential and the limitations of such features. In particular, we demonstrate how sub-6 GHz massive MIMO can successfully tackle cell selection and interference challenges, we showcase encouraging mmWave coverage evaluations in both urban and suburban/rural settings, and we examine the peculiarities of direct device-todevice communications in the sky. Moving on, we sneak a peek at next-generation UAV communications, listing some of the use cases envisioned for the 2030s. We identify the most promising 6G enablers for UAV communication, those expected to take the performance and reliability to the next level. For each of these disruptive new paradigms (non-terrestrial networks, cellfree architectures, artificial intelligence, reconfigurable intelligent surfaces, and THz communications), we gauge the prospective benefits for UAVs and discuss the main technological hurdles that stand in the way. All along, we distil our numerous findings into essential takeaways, and we identify key open problems worthy of further study.

Joint Activity and Blind Information Detection for UAV-Assisted Massive IoT Access

“…It is important to note that in the coherent GFRA type I and coherent GFRA type II schemes, the channels are assumed to be quasi-static for a relatively long time and accurate estimation of the CSI plays a pivotal role for achieving better DAD and DD performance. However, the acquisition of accurate CSI is challenging, especially for practical UAV-ground channels due to the complex propagation conditions [6]. In addition, the preambles/pilots allocated for CSI acquisition may not be efficient for application to IoT devices with low energy consumption requirements and small data packets [24], [25].…”

“…However, to the best of our knowledge, there exist no related discussions on this critical issue to date. In addition, both [25] and [26] considered the frequency-flat channel fading, which is impractical for UAV-based wide-area massive IoT access [6].…”

“…With their inherent properties such as flexibility, mobility, and adaptive altitude, unmanned aerial vehicles (UAVs) have been considered as an indispensable component in future integrated terrestrial and aerial 6G networks to efficiently support massive access for wide-area IoT [4], [5]. Due to the low-cost and low-energy consumption features of typical IoT devices, as well as the complicated propagation condition of UAV-ground channels, disruptive techniques are needed to efficiently enable UAV-enabled wide-area massive IoT access [6]- [10].…”

“…Based on the estimated X, in line 18, we can acquire the index of the selected signature sequence, i.e., supp{e j k, n }, of the k-th device in the n-th subcarrier for the j-th time slot, ∀k ∈ Ω, n ∈ [ N ], ∀j, by selecting the row of X j k, n that has the maximum power. Hence, we acquire the embedded information by exploiting the device activity observed at multiple receive antennas 6 . By performing line 16 and line 18, the DAD-EID process is achieved in a noncoherent approach without the need of explicit CSI.…”

What is A Wireless UAV? A Design Blueprint for 6G Flying Wireless Nodes

“…This way, UAVs implement a private service network that can be deployed on-demand as an alternative to the unavailable or untrustworthy cellular infrastructure [5,12]. • UAVs for 6G: UAVs will implement key 6G network infrastructure operating in the low atmosphere (< 1 km) which will connect ground users with the non-terrestrial 6G infrastructure deployed in-orbit (20 to 35786 km) [17].…”