Unmanned aerial vehicles (UAVs) are expected to become an integral component of future smart cities. In fact, UAVs are expected to be widely and massively deployed for a variety of critical applications that include surveillance, package delivery, disaster and recovery, remote sensing, and transportation, among others. More recently, new possibilities for commercial applications and public service for UAVs have begun to emerge, with the potential to dramatically change the way in which we lead our daily lives. For instance, in 2013, Amazon announced a research and development initiative focused on its next-generation Prime Air delivery service. The goal of this service is to deliver packages into customers' hands in 30 minutes or less using small UAVs, each with a payload of several pounds. 2014 has been a pivotal year that has witnessed an unprecedented proliferation of personal drones, such as the Phantom and Inspire from DJI, the Lone Project from Google, AR Drone and Bebop Drone from Parrot, and IRIS Drone from 3D Robotic. Such a widespread deployment of UAVs will require fundamental new tools and techniques to analyze the possibilities of wireless communications using UAVs and among UAVs. In the telecom arena, flying drones are already envisioned by operators to help provide broadband access to under-developed areas or provide hot-spot coverage during sporting events. More generally flying drones are expected to become widespread in the foreseeable future. These flying robots will develop a unique capability of providing a rapidly deployable, highly flexible, wireless relaying architecture that can strongly complement small cell base stations. UAVs can provide "on-demand" densification, help push content closer to the end-user at a reduced cost and be made autonomous to a large extent: Airborne relays can self-optimize positioning based on safety constraints, learning of propagation characteristics (including maximizing line of sight probability) and of ground user traffic demands. Finally UAVs can act as local storing units making smart decisions about content caching. Thus airborne relays offer a promising solution for ultra-flexible wireless deployment, without the prohibitive costs related to fiber backhaul upgrading. Yet another example is when UAVs can be used as flying base stations that can be used to serve hotspots and highly congested events, or to provide critical communications for areas in which no terrestrial infrastructure exists (e.g., in public safety scenarios or in rural areas). Clearly, UAVs will revolutionize the wireless industry and there is an ever increasing need to understand the potential and challenges of wireless communications using UAVs.
To this end, this tutorial will seek to provide a comprehensive introduction to wireless communications using UAVs while delineating the potential opportunities, roadblocks, and challenges facing the widespread deployment of UAVs for communication purposes. First, the tutorial will shed light on the intrinsic properties of the air-to-ground and air-to-air channel models while pinpointing how such channels differ from classical wireless terrestrial channels. Second, we will introduce the fundamental performance metrics and limitations of UAV-based communications. In particular, using tools from communication theory and stochastic geometry, we will provide insights on the quality-of-service that can be provided by UAV-based wireless communications, in the presence of various types of ground and terrestrial networks. Then, we will analyze and study the performance of UAV-to-UAV communications. Subsequently, having laid the fundamental performance metrics, we will introduce the analytical and theoretical tools needed to understand how to optimally deploy and operate UAVs for communication purposes. In particular, we will study several specific UAV deployment and mobility scenarios and we will provide new mathematical techniques, from optimization, game, and probability theory that can enable one to dynamically deploy and move UAVs for optimizing wireless communications. Moreover, we will study, in detail, the challenges of resource allocation in networks that rely on UAV-based communications. Throughout this tutorial, we will highlight the various performance tradeoffs pertaining to UAV communications ranging from energy efficiency to mobility and coverage. The tutorial concludes by overviewing future opportunities and challenges in this area.