Aeronautical Air-Ground Data Link Communications

By Mohamed Slim Ben Mahmoud, Christophe Guerber, Nicolas Larrieu and 2 more

This book deals with air-ground aeronautical communications. The main goal is to give the reader a survey of the currently deployed, emerging and future communications systems dedicated to digital data communications between the aircraft and the ground, namely the data link. Those communication systems show specific properties relatively to those commonly used for terrestrial communications. In this book, the system architectures are more specifically considered from the access to the application layers as radio and physical functionalities have already been addressed in detail in others books.

The first part is an introduction to aeronautical communications, their specific concepts, properties, requirements and terminology. The second part presents the currently used systems for air ground communications in continental and oceanic area. The third part enlightens the reader on the emerging and future communication systems and some leading research projects focused on this scope. Finally, before the conclusion, the fourth part gives several main challenges and research directions currently under investigation.

• Language: English
• Publisher: Wiley
• Release date: Dec 1, 2014
• ISBN: 9781119006855

Mohamed Slim Ben Mahmoud

Mohamed Slim Ben Mahmoud is a project leader at Altran since 2016. He's also a research engineer and associate professor at Ecole Natinale de l'aviation civile since 2013. He obtained a PhD in IT and Network Security, Aeronautical Data link Communications in 2012.

Book preview

Introduction

I.1. Objectives and motivations

In both contexts of constant increasing air traffic and migration of air–ground communications from analog voice to digital data, the current, emerging and future communication systems face a great challenge: providing efficient links with suitable capacity, availability and integrity.

During each flight phase, an aircraft has generally at least two means in order to communicate with the ground. Furthermore, the communication systems may be different depending on the considered airspace. For instance, in continental areas, direct links with ground stations can be provided whereas in oceanic areas satellite-based solutions represent an alternative solution.

Considering the offered services, aircraft communications are classified in two mains groups. First, cockpit services include both Air Traffic Services Control (ATSC) for pilots and controllers, and Air Operation Control (AOC). ATSC/AOC services are considered safety-related. Second, services can be also provided in cabin for airline administrative purposes Airline Administrative Communications (AAC) or for passengers. These latter services are considered non-safety related and in order to ensure a complete segregation between safety and non-safety services, they are based on dedicated communication systems.

As the traditional communications means for safety related services are about to reach their capacity limits, new solutions are proposed and several research projects aim at designing more efficient communication systems.

The migration from analog voice to digital data has already started and in order to prevent communication link congestion some new systems have been studied and even partially deployed, mainly for operational services. Some of these recent systems, such as VHF Datalink (VDL) or L-band Digital Aeronautical Communication System (LDACS), are based on line-of-sight links between aircraft and ground stations, thus limiting deployment to the continental domain. In oceanic areas, satellite-based systems are proposed as the main solution for aeronautical communications. Current satellite-based communication architectures dedicated to aeronautical data link operate in the L band (frequency range 1,525–1,660 Mhz).

The aviation industry and airlines are expecting researchers, engineers, technicians to define, design, deploy and maintain current and future aeronautical systems dedicated to air–ground data link communications.

At the same time, fixed and mobile ground public communication networks are growing exponentially following a revolution that started in the 1970s. Aeronautical communication means evolution should now ensure an easy inter-operation with existing ground systems while taking into account the constrained economic environment, by using well-known, field proven and validated protocols. Transport control protocol/Internet protocol (TCP/IP), which has been validated through several years of intensive use, is a good candidate. However, it has to be noted that as the aeronautical environment has particular properties and constraints, existing ground communication solutions and protocols should be adapted instead of being used as they are.

Even well-trained researchers, engineers or technicians in current ground networks and their protocol architectures may experience some lack of background information on the specific properties and constraints of the aeronautical environment and its organization, when they have to address aeronautical communication networks.

Hence, this book has several objectives. First, the co-authors want to provide the reader a way of discovering the field of aeronautical air–ground data link communications.

Second, this book aims to give a comprehensive overview of the current, emerging and future communication systems dedicated to data link in the context of aeronautical air–ground communications.

Third, the book should be able to provide some elements and information on research tracks for future aeronautical communication.

Finally, the co-authors want this book to be educational and informative for the readers (researchers, engineers, technicians or students, for instance) that already have some basic knowledge of data communication networks in order to quickly discover and understand the constraints, features and properties of aeronautical air–ground communication systems.

I.2. Organization of the book

After this introduction, Chapter 1 is devoted to the current communication radio systems for data link. Digital data oriented services began in the late 1970s with what would become the most widely used data link air–ground communication system: Aircraft Communications Addressing and Reporting System (ACARS). It provides airlines with the means to automate a part of their operations. With the emergence of data link ATSC applications intended to increase the efficiency of Air Traffic Control (ATC) communications, the industry had to define the supporting air–ground subnetwork. Thought of as an airline supporting system for their operations, ACARS could hardly meet the requirements of ATC users and applications, especially in dense airspaces with smaller separation standards. Thus, technical solutions have been introduced to cope with this issue. FANS 1/A, which encompasses an improvement of ACARS, is used mainly in oceanic and remote areas. At the same time, International Civil Aviation Organization (ICAO) started the definition of the Aeronautical Telecommunication Network, including their air–ground subnetworks. Among the different candidate technologies, VDL mode 2 is the one that has been chosen in Europe to support ATC communications. Aeronautical Telecommunication Network/VHF Data Link (ATN/VDL) mode 2 is incorporated within the framework of FANS 2/B and is currently deployed, either as an ATN subnetwork or as a supplementary subnetwork of ACARS.

Chapter 2 describes the emerging and future communication radio systems for data link. Several data link research projects investigate future needs and usages for such means of communication. In particular, new trends in this field of expertise, such as Quality of Service (QoS) provisioning, multilink communication system and advanced security services are addressed. Research projects highlighted in this chapter will be the two most important in this scientific area: the European project Single European Sky for ATM Research (SESAR) and the North American project Next Generation Air Transportation System (NextGen). This chapter continues with an introduction to the emerging communication systems able to provide new aeronautical application services. Three different candidate technologies are described: Aeronautical Mobile Airport Communication System (AeroMACS), LDACS and Satellite communication (SATCOM). Each of them represents a different access network providing specific means of communication depending on the type of aeronautical communication usages (continental and/or oceanic exchanges) needed by an airline. Each of these technologies will be technically described – advantages and drawbacks dealt with – to give, at the end of this chapter, a clear overview of the technical trends for aeronautical communication technologies in the near future.

Chapter 3 focuses on the challenges and research directions for future data link communication systems. The first part of the chapter discusses the foundations and challenges behind the deployment of the future System Wide Information Management (SWIM). The second part is dedicated to the multilink operational concept. Operational and communication requirements are addressed according to the different data link systems (i.e. AeroMACS, LDACS and Satellite-based systems). Specifically, the vertical handover issue is presented in-depth. The IEEE 802.21 candidate technology is considered with regards to a typical vertical handover scenario that might occur when all future data link systems will be deployed. In the next section, IP mobility requirements and protocol solutions are discussed from an aeronautical point of view. Open issues related to mobility support in aeronautical communications are also identified. As a very new but also very important area of research, segregation between operational and non-operational traffic is explained along with a proposal for airborne traffic separation based on priority and Quality of Service (QoS) management. Network security and communication-related certification issues are also exposed. Lastly, the final part of Chapter 3 goes one step beyond centralized networking approaches to ad hoc aeronautical networks whereby aircraft can establish links between themselves to achieve end-to-end communications between a ground station and an aircraft out of its coverage area. The section dedicated to Aeronautical Ad hoc Networks (AANETs) describes their properties and expected performances regarding operational, architectural and technological assumptions.

1

Current Communication Radio Systems for Data Link

1.1. History and definition

1.1.1. From voice to data link

The earliest communication with aircraft was by visual signaling using, for instance, colored paddles or hand signs. This communication means was mainly dedicated to ground crew but was not suitable for pilots. The first aeronautical radio link for air–ground communications was proposed at the beginning of the 20th Century. The first radio transmitter was invented and tested by AT&T in 1917. This allowed for the first time voice communications between ground personnel and pilots. After the First World War, new radio communication systems offering greater range and better performances were developed. But, it was only in 1935 that airborne radios were considered reliable and efficient enough to be widely deployed on existing aircraft.

These air–ground communication means were proposed in order to increase air safety. In the years that follwed, the Very High Frequency (VHF) band was mainly used for radiotelephony services between pilots and controllers. Even though the used technologies have, of course, evolved, the main principle is still the same today: the VHF-reserved bandwidth (today from 118 to 137 MHz also known as aircraft band or airband) is split into several channels with a spacing to ensure efficient sharing of resources. First, implementations were based on 140 channels with a spacing of 100 kHz. From 1979 to 1989, the bandwidth was split into 760 channels with a spacing of 25 kHz. And at the end of the 1990s, digital radio was introduced and greatly increased capacity by reducing the bandwidth required for speech transmission. Then, the airband (117.975–137 MHz) was split into 2,280 channels with a spacing of 8.33 kHz. In order to ensure the required availability, a voice communication uses either VHF or high frequency (HF) (from 3 to 30 MHz) voice radios. It has been further augmented with Satellite Communication (SATCOM) since the early 1990s. Hence, voice communications are possible even in oceanic areas where direct communications with VHF ground stations cannot be deployed due to their range.

Nevertheless, considering the increasing number of aircraft in the airspace at the same time, the lack of resources makes it necessary to first seek new solutions in order to avoid congestion. An innovative solution, known as data link or digital data link, is based on new solutions and ways to exchange between end users. Data link offers the ability to transmit short and relatively simple digital messages between aircraft and ground stations via communication systems that are today more often based on VHF or SATCOM. It was at the end of the 1970s that airlines were convinced by the advantages of communications based on data link. In July 1978, the engineering department at Aeronautical Radio Incorporated (ARINC) introduced the first data link means known as Aircraft Communications Addressing and Reporting System (ACARS). The objectives of this new way to communicate were to reduce crew workload and improve data integrity. This system, also known today as Plain Old ACARS (POA) and still in use in some airspace, uses VHF channels initially dedicated to voice communication. It operates at 2.4 kbps and was first used for communications dedicated to airlines. The word ACARS also refers to the messages’ format. The first application was Out, Off, On, In (OOOI) and has the aim to simplify the management of airlines crew members and particularly pilots. It allows communicating accurately and immediately when the aircraft leaves the gate, takes off, lands and so on. ACARS has been enhanced by new applications, and its use extended to other communication means such as SATCOM and HF links. And during the 1980s, air traffic control (ATC) authorities began to encourage the use of ACARS between controllers and pilots to