This chapter provides the background and context for unmanned aerial vehicles (UAVs) and UAV networks with a focus on their civilian applications. It discusses, for example, the types of UAVs, fuel, payload capacity, speed, and endurance. It will also discuss the state-of-the-art in engineering and technology aspects of UAVs and UAV networks and the advantages of UAV networks, including enhanced situational awareness and reduced latency in communications among the UAVs. It presents the applications of UAV networks, research opportunities, and challenges involved in designing, developing, and deploying UAV networks, and the roadmap for research in UAV networks.

Over recent decades, many different terms have been used to refer to UAVs, the most recent of which being remotely piloted aerial system (RPAS), which insists that the system is somehow always operated by somebody on the ground who is responsible for it. The term is very much like the old name for UAVs of the 1980s, that is remotely piloted vehicle (RPV). The RPAS puts emphasis on the fact that the aerial system includes not only the flying vehicle but also, for example, a ground control station, data link, and antenna. It also provides room for the case where several aircraft belonging to the same system may be remotely operated as a whole by a single human operator. In that case, it is not possible for the operator to actually control each flying vehicle as if he or she was an RC pilot.

Yet, in aeronautics, piloting an aircraft basically means flying an aircraft. It has a very precise meaning which is related to the capability to control the attitude of the vehicle with respect to its center of gravity. While most UAVs are remotely operated, they almost all have an on-board autopilot in charge of flying the aircraft. Therefore, it is not a remotely piloted vehicle but only a remotely operated vehicle where navigation commands are sent to the aircraft. Furthermore, navigation orders such as waypoints, routes, and decision algorithms may even be included in the on-board computer in order to complete the mission without human action along the way. In this way, human judgment is devoted to actions at higher levels, such as decision making or strategy definition. The term “remotely operated aircraft system” (ROAS) would therefore make more sense to the current scientific community.

Introduction

As the airspace is being opened up for UAS, the UAS market is expected to see a tremendous growth over the next two decades. One projection is that by 2035, there may be as many as 250,000 UAVs including commercial, public, state, and federally owned UAVs operating in the airspace providing various kinds of services in the United States alone [321]. Inclusion of such a large number of UAVs in the airspace creates many challenges in terms of safety, security, and privacy, which are the three dimensions for integrating UAVs in the airspace and for designing real-world applications. The three factors are not completely independent of each other as one factor influences the other two.

Safety of human lives, undoubtedly, is the most critical aspect for any manned or unmanned aircraft. Safety is achieved through advances in aviation technology and statutory regulations that will help to prevent potential collisions in midair or on the ground. Factors that influence decisions related to safety include price, performance, payload, and power needs among others. Trade-offs among these factors need to be carefully considered while making statutory regulations. For example, the type of collision avoidance technology that should be made mandatory through the federal regulation for aircraft should take into account the impact of the choice on the performance of the aircraft.

Information security is critical in the sense that revealing essential flight information to hackers may jeopardize the safety of the aircraft and people on the ground. Thus, information security is not independent of safety. For example, hackers can fabricate messages impersonating or spoofing a plane, creating ghost planes in the air. Information security measures are needed to distinguish false messages from true messages intended for safety and situational awareness. Similarly, measures for aviation security may have an impact on the privacy of citizens as our experiences at airports demonstrate. While citizens may accept to forego a certain amount of comfort for security, any measures that cause privacy concerns should be minimized.

In the light of UAV integration into airspace, information security and privacy issues that surround the use of UAVs are being re-investigated. Legal definitions of individuals’ privacy and information security are being re-examined in order to understand the trade-offs between the two.

Aviation authorities around the world have been making progress towards integrating UAVs (unmanned aerial vehicles) into their national airspaces. In parallel, private industry has been developing innovative UAV-based applications, such as drone-based package delivery, medicine delivery, pipeline monitoring systems, and disaster-area aerial surveys. However, before UAVs can become integrated into the civilian airspace and such real-world applications become reality, there are several technical, societal, and regulatory challenges that need to be addressed by the research community. The most important among them is the need for enhanced situational awareness of UAVs in the airspace.

Three different, yet complementary, paradigms emerged to address enhanced situational awareness of UAVs: satellite communications, cellular-communications, and aerial communications and networks. This book focuses on the third strategy, i.e., enhanced situational awareness through self-organized aerial networking of UAVs. It provides the necessary knowledge for students, researchers, and professionals to gain an understanding of the research challenges in UAV networks and communications. Collaborating with several eminent research scholars and subject matter experts, the editors developed nine chapters that take the reader from the foundations to active research topics in this exciting domain.

The first chapter, “Introduction to UAV Systems,” introduces the reader to UAV types and missions. It provides the background and context for UAVs and UAV networks with a focus on their civilian applications. It also discusses the state-of-the-art in engineering and technology aspects of UAV networks and the benefits of deploying such networks.

The second chapter, “Air-to-Ground and Air-to-Air Data Link Communication,” provides the background on wireless communication used in manned aviation. It discusses the technologies proposed for L-band Digital Aeronautical Communication. It provides the fundamental insights relevant for aerial communication on unmanned and small UAVs, learned from experience with the advanced terrestrial mobile broadband communication extrapolated to the aerial case.

The third chapter, “AerialWi-Fi Networks,” provides the characteristics of aerial links in three-dimensional space (3D). Aerial networks differ from other wireless networks, such as mobile ad hoc networks or vehicular ad hoc networks. It discusses the communication requirements for aerial network applications in terms of throughput, delay, data exchange frequency, etc. It defines different levels of autonomy in aerial networks from the perspective of communication needs.

Introduction and Background

Recent technological progress, especially in robotics and mechatronics, has made it possible to create autonomous mobile vehicles such as air, ground, surface, or underwater robots. All of these vehicles are referred to as drones or unmanned systems. The focus of this chapter is on air vehicles, but all these systems share a large number of characteristics independently of the environment in which they evolve. This chapter is thus useful reading whatever type of unmanned system you are interested in. Unless stated otherwise, the term drone in what follows will refer to air vehicles.We will also use the terms unmanned aerial vehicle (UAV), unmanned aerial system (UAS), and remotely piloted aircraft system (RPAS), the latter being the now official naming. It should be noted that the wording RPAS includes the notion of a remote pilot. Still, in this chapter, the focus is on autonomous systems that do not have a ground pilot, and that consequently need to make their own decisions to achieve the missions that are assigned to them. Why we consider autonomous drones will be explained a bit later in this introduction.

The technological progress additionally makes it possible to embed various sensing, actuating, and communication capabilities on board drones and it is now possible for them to not only interact with their environment (by means of sensors and actuators) but also to interact with each other (and with the ground, surface, or underwater vehicles, ground sensors, and troops). It is thus possible to consider groups of UAVs flying together and collaborating to achieve a common global mission.1 Such groups are referred to as swarms. Swarms usually assume close collaboration and close flight – even though close flight still remains a difficult problem – whereas a fleet – terminology that the reader will often find in the literature – supposes looser relationship and a notion of hierarchy between the UAVs. In this chapter, we will use both words depending on the kind of configuration we are referring to. Additionally, we are envisioning large groups of drones and since one cannot afford to have as many ground pilots as UAVs (we are talking tens or hundreds of UAVs), the UAVs we consider have to be autonomous: once launched, they manage themselves without any ground intervention.

Introduction

Traditional Internet protocols are not suitable for the aeronautical environment. The TCP/IP protocol stack has evolved for an Internet that is mostly wired (although that is changing at the edges) with stable topologies and connectivity to which disruptions require terminating of TCP connections, and reconvergence of routing algorithms.

Civilian and commercial airborne networks require some modifications due to wireless links and moderate but often predicable mobility. However, these scenarios are not necessarily multi-hop, and traditionally rely on point-to-point links to ground stations for ATC (air traffic control) and satellites (for Internet access and entertainment distribution). Drone networks may be more challenging if multi-hop communication is desired with unpredictable movements.

The most challenging scenario is for highly dynamic high-velocity multi-hop airborne networks, currently the domain of military communication. However, it is reasonable to expect future civilian, commercial, and government airborne networks to become more challenging as is becoming the case for ground-based vehicular networks, motivating VANETs (vehicular ad hoc networks) and VDTNs (vehicular disruption-tolerant networks).

This chapter is organized as follows: Section 4.2 introduces the communication environment for aeronautical networks, which can vary significantly depending on the scenario (e.g., civilian vs. military networks). Section 4.3 relates airborne networks to the traditional Internet, as well as other mobile wireless environments, including WMNs (wireless mesh networks), MANETs (mobile ad hoc networks), and DTNs (disruption-tolerant networks). Section 4.4 then presents an architecture and protocol suite suitable for the most demanding aeronautical environment: highly dynamic, high-velocity multi-hop networks that require the greatest change to past networking architectures, with comparisons to traditional end-to-end transport and routing protocols. Section 4.5 presents selected performance evaluation of this aeronautical protocol suite, with references to further analysis. Finally, Section 4.6 summarizes this chapter.

Airborne Network Environment

Airborne networks are a class of mobile wireless networks: wireless due to the untethered communication links between aircraft, and mobile due to the movement of aircraft. Depending on the communication paradigm, they may or may not need to be ad hoc networks that self-organize.

Table 4.1 shows the key characteristics of airborne network scenarios, ordered in increasing challenge to network protocols. The evolution from current to future network types, described for each scenario below, is depicted in italic font in the last column.

This chapter discusses the design, implementation and deployment of an unmanned aerial vehicle (UAV) network for the purpose of transmitting video surveillance data amongst nodes. It presents a heterogeneous network consisting of multiple stationary and mobile ground-based nodes, as well as multiple autonomous aerial vehicles. A design process to enable emergent system safety in an Unmanned Aerial Vehicle Platform System through the correct integration of critical UAV subsystems in a scalable fashion to enable collaboration across multiple UAVs is outlined. The UAV network system field demonstration comprised of 16 fixed ground nodes, 1 mobile ground node, and 2 airborne nodes connected by two routing gateways to a legacy wired network is described. Networking and communications effects, including the impact of node mobility, network partitioning and merging, as well as gateway failovers are examined through the course of the demonstration. Discussion of the networking protocols deployed, as well as analysis of performance issues are then placed in context of the overall field demonstration.

Unmanned Aerial Vehicle (UAV) Platform Systems

The Aerospace Laboratory for Embedded Autonomous Systems (ALEAS) Unmanned Aerial Vehicle (UAV) platform system consists of several individual Unmanned Aerial Vehicles (UAVs). Each system had a common architecture along with attendant ground stations which can be used to relay commands, as well as operational procedures, to the UAVs if needed. Amodular software infrastructure was then used to enable collaborative UAV flight [361]. The main purpose of the UAS platform was to develop assurance methods to enable autonomous flight of UAVs in a shared airspace environment, such as the National Airspace System (NAS). Thus, a primary concern was making sure that the system exhibits high safety and reliability standards. The field demonstration [125], further detailed in Section 5.2.1, required that a video be streamed across a network comprised of both ground and aerial nodes. As fielded in the outlined experiment, the UAS system consisted of two UAVs, continuously operating at an altitude of approximately 100–300ft. above ground level for roughly 50 minutes each.