2.1. Data link related research projects
2.1.1. Topics of interest
Emerging and Future Communication Radio Systems for Data Link
2.1. Data link related research projects
Communication Infrastructure (FCI). These technologies, which will provide a smooth transition from a final user point of view, are:
– L-band Digital Aeronautical Communication System (L-DACS): under the EUROCONTROL/FAA Action Plan 17 (AP17) activities, the L-band has been identified as the best candidate band for continental communications, mainly due to its propagation characteristics. Two options for L-DACS, referred to as L-DACS1 and L-DACS2, respectively, have been considered so far, each one having its own specifications. The first option uses a Frequency Division Duplex (FDD) access scheme with an Orthogonal Frequency Division Multiplexing (OFDM) modulation. The second option, inspired from the commercial Global System for Mobile Communications (GSM) standard, is a Time Division Duplex (TDD) technology with a Gaussian Minimum Shift Keying (GMSK) modulation.
Both options rely on completely different approaches: while L-DACS2 capitalizes on existing systems and their proven performances, L-DACS1 uses advanced and modern modulation and network protocols. The SESAR program is currently in charge of prototyping, testing and validating both versions of the system. The final selection process will be made in a global framework involving International Civil Aviation Organization (ICAO) by 2022. L-DACS is described in detail in section 2.2.2.2;
– Aeronautical Mobile Airport Communication System (AeroMACS) is a C-band data link system based on mobile WiMAX IEEE 802.16e [IEE 09]
dedicated to airport operations. The EUROCONTROL/FAA AP17 selected WiMAX as a basis for AeroMACS because of its specific characteristics that are compliant with communication requirements and constraints inherent to the airport surface. Indeed, the IEEE 802.16-2009 standard supports non- Line of Sight (LoS) communications, mobility for moving vehicles and aircrafts, provides a built-in Quality of Service (QoS) and security framework, not to mention its flexibility and scalability in the architecture definition. Aeronautical standardization bodies are currently working on the final AeroMACS profile, the validation process has already started throughout testbeds in Europe (Toulouse) and USA (NASA). In section 2.2.2.1, the AeroMACS network architecture and both physical layer (PHY) and MAC layers are depicted;
– satellite-based systems possess the required capabilities to cover oceanic airspace communications, which is not the case of L-DACS and
AeroMACS. The technology is also meant to complement continental data link communications in order to satisfy the high demand of operational services. The aeronautical-dedicated satellite system is currently defined jointly with the European Space Agency (ESA). Main satellite projects and foreseen network architectures are described in section 2.2.2.3.
2.1.1.2. Aeronautical network services
To achieve a progressive and successful integration of these data link technologies into the existing ATM environment, research projects and programs identified several working areas. Supporting heterogeneous technologies in the same context requires close management of the following network services:
– multilink support: as mentioned above, the FCI encompasses three access networks, each one relevant to a given data link technology.
The Multi Link Operational Concept (MLOC) implies that at least two future independent air–ground data link systems are simultaneously available and used to achieve high availability and communication continuity. While the multilink concept has undeniable advantages, particularly for safety services, it requires specific efforts to make the overall network responsive and compliant with stringent QoS requirements. These efforts have to cover vertical handover, end-to-end security throughout the flight, Required Communication Technical Performances (RCTPs) achievement, without compromising the flight operations;
– mobility: the need for mobility support is inherent to the MLOC and the mobile nature of aircrafts. For instance, suppose that an aircraft has established a communication with the air traffic control (ATC) tower using the AeroMACS system before taking off. Once the aircraft leaves the airport coverage airspace, it has to switch to the L-DACS access network. As the FCI will be based on Aeronautical Telecommunication Network/Internet Protocol Suite (ATN/IPS), the aircraft has to acquire a Care of Address (CoA) in the visited IP subnetwork. Service continuity is then a prerequisite for a seamless handover when the aircraft is moving from an Air Navigation Service Provider (ANSP) network to another;
– QoS management: the provision of a service with stringent performances is required for the FCI. The usual QoS requirements, which can be found in the literature, are still needed in the context of the FCI, with a particular focus on high availability and strict transmission delays. For
instance, 0.9995 service availability is quoted more than once for operational messages in EUROCONTROL technical documents [EUR 07]. Additionally, separation between operational and non-operational domains represents another design challenge for the future network infrastructure. Such a separation could be achieved at different layers of the protocol stack (i.e.
physical, link and network layers), all these possibilities are currently considered by the supporting research programs;
– security: one of the most challenging issues. Security must be taken into account in the design of all new emerging data links, but also in the applications and services themselves. From a robustness point of view, an end-to-end security covering all the aspects of the FCI is highly recommended as the consequences of a cyber-attack might be irreversible, involving not only loss of data or connectivity, but also human lives in most critical situations. The NextGen and SESAR contributors are paying a particular attention to security, several Work Packages (WPs) are dedicated to address cyber security in each program.
These fundamental services for the FCI are discussed in details in section 3.2.