What Will the Future of UAV Cellular Communications Be? A Flight from 5G to 6G (2105.04842v1)

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-to-device 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, cell-free 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.

• The paper presents a comprehensive analysis of the transition from 5G’s mmWave and massive MIMO techniques to emerging 6G innovations such as NTNs and AI-driven mobility management.
• It evaluates current 5G NR methods, demonstrating how beamforming and advanced interference cancellation enhance UAV-to-base station association.
• The study proposes forward-looking 6G enablers, including cell-free architectures and reconfigurable intelligent surfaces, while outlining critical research challenges for scalable aerial networks.

Overview of UAV Cellular Communications Evolution from 5G to 6G

The paper "What Will the Future of UAV Cellular Communications Be? A Flight from 5G to 6G" provides a comprehensive analysis of the evolution of unmanned aerial vehicle (UAV) communication systems as they transition from 5G to 6G technologies. This work distinguishes itself by integrating both academic and industry perspectives to propose realistic UAV use cases, assess the efficacy of current 5G New Radio (NR) features, and forecast 6G enablers likely to revolutionize UAV communications in the forthcoming decades.

The analysis starts with an examination of 5G capabilities, notably the integration of sub-6 GHz massive MIMO and mmWave technologies. The paper confirms that while massive MIMO effectively addresses cell selection and interference issues, the beamforming flexibility in NR can ameliorate UAV-BS association problems, allowing UAVs to leverage stronger signals primarily through resilient sidelobes and reflections. Furthermore, mmWave holds the promise of significant throughput benefits through directional transmissions. However, the limitations associated with current deployment densities are noted, highlighting the potential need for supplementary infrastructure to ensure persistent, high-capacity connectivity, especially in urban environments.

The Paradigm Shift to 6G

In looking beyond 5G, the paper identifies key use cases such as 3D aerial highways, which herald changes not only in technology but also in societal and business paradigms. The expected proliferation of UAVs necessitates innovations that go beyond traditional cellular architectures. Here, the paper explores five anticipated 6G technologies:

1. Non-Terrestrial Networks (NTNs): These networks are projected to play a critical role in filling terrestrial coverage gaps, boasting blanket LoS coverage critical for BVLoS. However, challenges inherent in hardware miniaturization and protocol design for cross-layer NTN integration remain pivotal hurdles.
2. Cell-Free Architectures: By transforming intercell interference into usable signals, cell-free architectures could enhance UAV communication, especially given the typically strong LoS potential between UAVs and multiple base stations. The effectiveness of these architectures has profound implications for reliability and throughput in dense UAV swarms.
3. AI: AI will be central, not merely in channel modeling but also in mobility management, offering improved handover protocols and resource allocation strategies by leveraging reinforcement learning and other machine learning paradigms.
4. Reconfigurable Intelligent Surfaces (RISs): RISs promise to manipulate electromagnetic waves to enhance signal quality through controlled reflections/refractions, thus tackling potential issues of shadowing in complex environments.
5. THz Communications: Despite formidable challenges related to power consumption and channel characterization, the expansive bandwidth of THz frequencies offers exceptional capacity, potentially meeting real-time transfer and precision localization requirements for advanced UAV applications.

Implications and Future Research Directions

This paper does not shy away from identifying the technological and practical challenges associated with each 6G enabler. Areas highlighted for further research include the development of scalable, interference-cognizant multi-access schemes, UAV-specific fractional power control mechanisms, and robust cross-band backhauling solutions. This paper is a call to the wireless research community to engage with these multifaceted challenges, suggesting that solutions will not only require advancements in wireless technologies but also an interdisciplinary approach blending telecommunications, AI, material science, and regulatory strategy.

In closing, while the paper presents a rich narrative on the transition from 5G to 6G UAV systems, it equally underscores the necessity for forward-thinking research to address the idiosyncrasies of aerial communication. Balancing the connectivity, coverage, and command demands will be crucial in realizing the potential of UAVs in a 6G world.