Unmanned aerial vehicles (UAVs) have found numerous applications and are expected to bring fertile business opportunities in the next decade. Among various enabling technologies for UAVs, wireless communication is essential and has drawn significantly growing attention in recent years. Compared to the conventional terrestrial communications, UAVs' communications face new challenges due to their high altitude above the ground and great flexibility of movement in the threedimensional (3D) space. Several critical issues arise, including the line-of-sight (LoS) dominant UAV-ground channels and resultant strong aerial-terrestrial network interference, the distinct communication quality of service (QoS) requirements for UAV control messages versus payload data, the stringent constraints imposed by the size, weight and power (SWAP) limitations of UAVs, as well as the exploitation of the new design degree of freedom (DoF) brought by the highly controllable 3D UAV mobility. In this paper, we give a tutorial overview of the recent advances in UAV communications to address the above issues, with an emphasis on how to integrate UAVs into the forthcoming fifth-generation (5G) and future cellular networks. In particular, we partition our discussions into two promising research and application frameworks of UAV communications, namely UAVassisted wireless communications and cellular-connected UAVs, where UAVs serve as aerial communication platforms and users, respectively. Furthermore, we point out promising directions for future research and investigation.
KeywordsUnmanned aerial vehicle (UAV), wireless communication, cellular network, channel model, antenna model, energy efficiency, air-ground interference, 3D placement and trajectory, optimization.
TechnologyDescription Advantages Disadvantages
Direct linkDirect point-to-point communication with ground node Simple, low cost Limited range, low data rate, vulnerable to interference, non-scalable Satellite Communication and Internet access via satellite Global coverage Costly, heavy/bulky/energyconsuming communication equipment, high latency, large signal attenuation Ad-hoc network Dynamically self-organizing and infrastructure-free network Robust and adaptable, support for high mobility Costly, low spectrum efficiency, intermittent connectivity, complex routing protocol Cellular network Enabling UAV communications by using cellular infrastructure and technologies Almost ubiquitous accessibility, cost-effective, superior performance and scalability Unavailable in remote areas, potential interference with terrestrial communications and high reliability/throughput for both air-to-air and airto-ground wireless communications in the three-dimensional (3D) space. Towards this end, four candidate communication technologies are listed and compared in Table III, including i) direct link; ii) satellite; iii) ad-hoc network; and iv) cellular network. In the following, we discuss the advantages as well as limitations of each of these technologies in detail.1) Direct Link: Due to its simpli...
