3.6. Future aeronautical communication means
3.6.4. AANET communications performances
Because TCPs propose several functionalities in order to adapt its throughput or sending rate to the network congestion, we use this protocol in our assessment. Hence, we have developed a simulation model for AANET.
In our model, we can choose the number of aircraft numbers, and also the number of ground stations. Aircraft positions are defined using the same method and inputs data used in our homemade tool. Regarding physical layer properties, the capacity of each interaircraft link is set to 1 Mbps. To determine the available throughput per aircraft, a path to the ground station has to be chosen. As a simple approach, we use the shortest path to the closest ground station, given by the Dijsktra algorithm. We thus obtain a list of edges representing the path from each aircraft to the ground station. The maximum distance to establish a connection between two aircraft (their communication range) is a simulation parameter.
At each time of the simulation, we consider a graph, whose nodes are aircraft and ground stations, and whose edges are the available connections between them. We assume that a connection based on ground network infrastructure is always available between all pairs of ground stations. The weight of each edge in the graph is its length. Then, the Dijkstra algorithm is used to find in this graph the shortest path from each aircraft to a ground station. It gives for each connected aircraft a path to the closest ground station.
Finally considering the application level, as the idea is to assess the available throughput for each aircraft. In our model, we use greedy TCP sources. Such TCP sources generate new TCP segments as soon as the previously sent ones are acknowledged. Hence, data are generated at the highest possible rate regarding the AANET congestion.
Table 3.3 shows the mains results we obtained after a simulation campaign. These results help to analyze the different scenarios. In our continental airspace, the mean aircraft throughput is 38.3 kbps with a maximum packet delay on the path between the aircraft and ground station of 551 ms for 95% of the packets (mean delay: 401 ms). In the studied
oceanic airspace, the mean throughput is 68.2 kbps with a maximum packet delay of 426 ms for 95% of the packets (mean delay: 184 ms). These better performances in oceanic airspace are mainly explained by the fact that, in the considered oceanic airspace, during one day there are a maximum of about 400 simultaneous flying aircraft (with a mean of 275 aircraft) for eight ground stations. Comparatively, in the French sky, our case study for continental area, the Peak Instantaneous Aircraft Count (PIAC), is near 600 aircraft with a mean of 500 simultaneous flying aircraft between 6:00 and 21:00 for five ground stations.
Mean aircraft throughput
Max delay 95% pk (ms)
Mean delay (ms)
Continental 38.3 551 401
Oceanic 68.2 426 184 Table 3.3. Shortest path routing results
These results may let us think that the obtained aircraft throughputs are quite low but considering the performances of the currently used systems (or even those that will be soon deployed), the proposed approach looks like a promising solution. For instance, the satellite system dedicated in L-Band for aeronautical communication and particularly the future satellite designed by ESA in IRIS program should provide a capacity of 1 Mbps that will be shared between a PIAC of at least 500 aircraft. In the worst case, a mean throughput of 2 kbps by aircraft could then be achieved. For VDL mode 2 communication system, which is currently deployed in Europe for continental air–ground communications, the offered capacity is 32.5 kbps for all the aircraft covered by a single ground station cell. A VDL mode 2 ground station has a maximum range of 200 nautical miles and may hence cover up to 200 aircraft. So regarding these estimations, the proposed solution based on AANET for air–ground communications shows good results, more so in the light of the expected low deployment and operational costs.
As an example of a realistic application, we consider one proposed by the BEA (Bureau of Enquiry and Analysis for Civil Aviation Safety), which is the French authority responsible for safety investigations into accidents or incidents in civil aviation. The main objective of this application is to facilitate data recovery from flight recorders by periodically sending flight
parameters to the ground in oceanic airspace. Three sets of parameters that should be sent each second for a given aircraft have been defined. The bulkier set has a size of 12,288 bits. So, we created a specific model in a new simulation scenario that allows each aircraft to behave as if it sends a set of flight data of 12,288 bits each second. Of course, this type of traffic source exhibits higher burstiness than the one used in the previous part. The simulation results show that all packets arrive with success to the ground station. The maximum observed delay for 95% of packet is 178 ms. The proposed innovative communication system is, therefore, compatible with such a realistic application.
For all these reasons, the AANET represents a good candidate for air–
ground communications and deserves further work, for instance, to improve routing performances, or to demonstrate its compatibility with other realistic applications.
Conclusion
In this book, a comprehensive overview of the current, emerging and future communication systems dedicated to data link in the context of aeronautical air–ground communications has been proposed.
The specific constraints and properties regarding legacy ground communication systems have been given. Network architectures and communication protocols have also been described with the aim of providing the readers details on system functionalities and properties. For instance, among the different candidate technologies, VHF Data Link (VDL) mode 2 is the one that has been chosen to support Air Traffic Control (ATC) communications in dense continental area like in Europe. 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 Aircraft Communications Addressing and Reporting System (ACARS). In Europe, a first step in the switch of ATC procedures from voice to data links relies on VDL mode 2 for the implementation of the Controller Pilot Data Link Communication (CPDLC) service.
Civil aviation organizations and airlines are facing challenges in terms of efficiency that involves increasingly intensive data exchanges. Thus, the long-term objective of substituting data exchange with voice as primary air control means implies a significant increase in available capacity as well as in reliability and availability. The challenge is then to cope with the air traffic increase by allowing the use of more dense trajectories and optimizing the workload of air traffic controllers. The connected aircraft is an
opportunity for airlines to optimize their maintenance procedures and facilitate the work of crews. Indeed, to deal with future data link needs and services, the industry and research community have structured their work on future communication radio systems with two leading projects: Single European Sky for ATM Research (SESAR) and Next Generation Air Transportation System (NextGen). In both projects, different communication technologies, which are currently investigated, can be considered as pertinent candidates for future data link communication technologies.
Indeed, three different communication means for data link systems have been considered depending on their connectivity range. The first one, dedicated to data link communication in the short-range location of the airport, is the Aeronautical Mobile Airport Communication System (AeroMACS) communication system. The second one, L-band Digital Aeronautical Communication System (L-DACS), is the candidate technology for continental data link communications. Different technologies could have been selected, but L-DACS seems to be the best one according to its propagation characteristics and the congestion level of the whole aeronautical frequency spectrum. The last communication system, Satellite Communication (SATCOM), is naturally dedicated to oceanic communications according to the specificities of SATCOMs, but a usage over continental regions is considered for link redundancy. These three different technologies are complementary and merging them will provide a worldwide communication system for future data link user needs.
Several persisting challenges or still investigated research fields have been presented in the last chapter of this book in order to introduce the readers to some of the future trends in aeronautical data link. Several important scientific issues and challenges associated with data link aeronautical communications have been risen, such as network security (i.e.
security overhead, defense in depth and traffic class priorities), the integration of heterogeneous services and access technologies (operational and non-operational services on the same access link), Internet protocol (IP) mobility issues (e.g. handover and scalability), and the multilink concept (i.e.
how to seamlessly use several access technologies along the flight lifecycle).
Finally, this book summarizes the current state of the art of air–ground data link communications for Air Traffic Management (ATM). Every candidate for future communication technologies has been described extensively, and its scope of application has been explained thoroughly.
However, the scope of ATM communications is a continuously evolving scientific field, and it is highly possible that some of the technologies described in this book will be replaced by some better performing technologies in the middle-term future. However, the difficult part of ATM communication system design is related to the dependability of all the different entities and systems involved in the communication more than to the complexity of a specific technology used by ATM designers. Given that, we hope this book will represent a sound and interesting technical reference for engineers interested in the field of ATM communications for the next decade.
Appendix
List of Acronyms
AAC Airline Administration Communications AADS Airplane Assets Distribution System AANET Aeronautical Ad Hoc Networks
ACARS Aircraft Communications Addressing and Reporting System ADS Automatic Dependent Surveillance
ADS-B Automatic Dependent Surveillance – Broadcast ADS-C Automatic Dependent Surveillance – Contract AeroMACS Aeronautical Mobile Airport Communication System AES Aeronautical Earth Station
AFN Air traffic services Facilities Notification AIS Aeronautical Information Services AMHS ATS Message Handling System AMS ACARS Message Security
AMSS Aeronautical Mobile Satellite Services ANSP Air Navigation Service Provider
AOA ACARS Over AVLC
AOC Aeronautical Operation Control
APC Aeronautical Passenger Communications ARQ Automatic Repeat request
ARTES Advanced Research in Telecommunications Systems
ASN Access Service Network
ATC Air Traffic Control
ATIS Automatic Terminal Information Service ATM Air Traffic Management
ATN Aeronautical Telecommunication Network ATS Air Traffic Services
ATSC Air Traffic Services Control AVLC Aeronautical VHF Link Control AWG Aviation Working Group BGP Border Gateway Protocol
BIS Boundary Intermediate Systems BPSK Binary Phase-Shift Keying
BS Base Station
CATMT Collaborative Air Traffic Management Technologies CDM Collaborative Decision Making
CDMA Code Division Multiple Access
CID Connection Identifier
CLNP ConnectionLess Network Protocol CLTP ConnectionLess Transport Protocol
CM Context Management
CNS Communication, Navigation and Surveillance
COCR Communications Operating Concept and Requirements for the Future Radio System
COTP Connection Oriented Transport Protocol CPDLC Controller Pilot Data Link Communication CRC Cyclic Redundancy Check
CSC Common Signaling Channel CSMA Carrier Sense Multiple Access
CSN Connectivity Service Network
CSS Common Support Services
CTS Clear To Send
DCE Data Circuit-terminating Equipment
DCL Departure Clearance
DGAC Direction Générale de l’Aviation Civile (French Civil Aviation Authority)
DHCP Dynamic Host Configuration Protocol DLE Data Link Entity
DME Distance Measuring Equipment DMU Data Management Unit DS-CDMA Direct Sequence CDMA DSP Data link Service Provider D-VOLMET Digital VOL METéorologique
DVB-RCS Digital Video Broadcasting-Return Channel via Satellite
ENAC Ecole Nationale de l’Aviation Civile (French Civil Aviation University)
ESA European Space Agency
E-SSA Enhanced Spread Spectrum Aloha
EUROCAE European Organisation for Civil Aviation Equipment
FAA Federal Aviation Administration FANS Future Air Navigation System
FCI Future Communication Infrastructure FDMA Frequency Division Multiple Access
FMS Flight Management System
GES Ground Earth Station
GMSK Gaussian Minimum Shift Keying GSIF Ground Station Information Frame
GSM Global System for Mobile Communications
HA Home Agent
HDLC High-Level Data Link Control
HF High Frequency
HFDL High Frequency Data Link H-NSP Home Network Service Provider HSRP Hot Standby Router Protocol
ICAO International Civil Aviation Organization IDRP Inter Domain Routing Protocol
IEC International Electro technical Commission IEEE Institute of Electrical and Electronics Engineers IETF Internet Engineering Task Force
IP Internet Protocol
IPSec Internet Protocol Security
IS Intermediate System
ISAE- SUPAERO
Institut Supérieur de l’Aéronautique et de l’Espace (French Aerospace Engineering School)
ISRM Information Service Reference Model
ITU International Telecommunication Union JCAB Japanese Civil Aviation Authority
LAN Local Area Network
L-DACS L-band Digital Aeronautical Communication System LME Link Management Unit
LTE Long Term Evolution MAC Medium Access Control
METAR Meteorological Aerodrome Report MF Medium Frequency
MF-TDMA Multi Frequency – Time Division Multiple Access MIAM Media Independent Aircraft Messaging
MIES Media Independent Handover Event
MIP Mobile IP
MITM Man In The Middle
ML OP Multilink Operational Concept
MPLS Multi-Protocol Label Switching
NAP Network Access Point
NAS National Airspace System (USA)
NAT North Atlantic Tracks
NEXTGEN Next Generation Air Transportation System NIDS Network Intrusion Detection System NSPs Network Service Provider
OCL Oceanic Clearance
OFDM Orthogonal Frequency Division Multiplexing ORP Oceanic Remote Polar
OSI Open Systems Interconnection
OVSF Orthogonal Variable Size Factor PENS Pan European Network System
PM-CPDLC Protected Mode – Controller Pilot Data Link Communication
POA Plain Old ACARS
PDU Protocol Data Unit
PKI Public Key Infrastructure QAM Quadrature Amplitude Modulation QoS Quality of Service
QPSK Quadrature Phase-Shift Keying
RFC Request For Comment
RSVP Resource Reservation Protocol RTCA Radio Technical Commission for Aeronautics RTCP Real-time Transport Control Protocol
RTS Request To Send
SAR Segmentation And Reassembly SARPS Standards and Recommended Practices SCPC Single Channel Per Carrier
SESAR Single European Sky for ATM Research SIGMET Significant Meteorological Effects
SLA Service Level Agreement
SNDCF Sub-Network Dependent Convergence Functions
SSB Single Side Band
SU Signaling Unit
SVC Switched Virtual Circuits SWIM System Wide Information Management TCP Transport Control Protocol
TDMA Time Division Multiple Access
TMA Terminal Area
TLS Transport Layer Security UDP User Datagram Protocol
UHF Ultra High Frequency
ULCS Upper Layer Communications Services UMTS Universal Mobile Telecommunications System
VDL VHF Data Link
VHF Very High Frequency VME VDL Management Unit
V-NSP Visited Network Service Provider VRRP Virtual Router Redundancy Protocol
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