LDACS stands for L-band Digital Aeronautical Communications System. It is the upcoming standard for digital, terrestrial aeronautical radio and thus an important data link technology within the future communications infrastructure for aviation. 

Currently, much of air traffic management (ATM) is handled via analog voice radio. This has the following disadvantages:

• An air traffic controller can only operate a relatively small control sector.
• Pilots must manually enter the new sector frequency in the cockpit when changing each control sector.
• Analog communication is inefficient because of the need to wait for readbacks and confirmations of receipt of messages in both directions.
• Analog radio requires a lot of bandwidth and is therefore spectrally very inefficient. This leads to capacity constraints in communications due to the growing number of aircraft.
• Analog radio has no cyber security measures to defend against deliberate interference and tampering.

This means that comprehensive modernization and digitization of air traffic management is needed to ensure safe, efficient and environmentally friendly air transportation in the future, despite increasing air traffic density. This modernization is taking place worldwide in large-scale projects, such as SESAR (Single European Sky ATM Research) in Europe or NextGen (Next Generation Air Transportation System) in the USA. In order for the newly developed ATM concepts to be used in civil aviation, a technology modernization of the underlying infrastructure for communications, navigation and surveillance (CNS) is required.

Establishment of a "Future Communications Infrastructure"

In aviation communications, this involves the transition from analog voice radio to digital data transmission. Since no single data link can cover communications in all phases of flight, ICAO has agreed to establish the Future Communications Infrastructure (FCI). This consists of several different data links - an airport data link, a satellite component, a ground-based data link and direct on-board communication between aircraft. By intelligently switching between the different data links, all phases of flight can be reached from the ground without interruption. The Aeronautical Mobile Airport Communications System (AeroMACS) has already been standardized for airport communications. For the satellite component, commercial providers for aviation applications are available in the form of Inmarsat and Iridium. For the ground-based data link, the first digital data link, VDL Mode 2, has been available since 1990, but it is technologically very outdated and has very limited performance. The implementation of modern ATM procedures (SESAR, NextGen) and the introduction of effective cyber security concepts require the use of a modern, high-performance data link.

LDACS provides this capability and is thus an important enabler for high-performance and efficient air traffic. Apart from higher data rates, LDACS offers modern message prioritization, unlike previous terrestrial aeronautical data links. This ensures that emergency situations can be responded to immediately. In addition to modern IP-based data traffic, LDACS supports a digital voice concept with low latencies, so that from the perspective of pilots and air traffic controllers, there is fundamentally little change to their operational processes. At the same time, it lays the foundation for new flight control concepts that were inconceivable with previous technology. In addition to the actual data transmission, LDACS offers the possibility of navigation via multilateration, in that the signals from at least four ground stations are evaluated by the aircraft and the location of the aircraft can thus be determined. In addition, the LDACS signals can be used by the aircraft on the ground to monitor the airspace. This makes LDACS the world's first true integrated CNS system.

Partners and Standardization

Together with Eurocontrol, Frequentis AG and the University of Salzburg, DLR was the initiator of the future airborne radio LDACS and contributed significantly to its design and development from the very beginning. Several projects under SESAR and the Aeronautics Research Program (LuFo) were applied for and successfully completed together with partners to further develop the technology maturity of LDACS. In 2016, the standardization of LDACS was initiated together with partners within ICAO. The LDACS standardization group "Project Team Terrestrial Data Link" established for this purpose is headed by DLR.

For more information, visit www.LDACS.com

Our Contribution

The DLR Institute of Communications and Navigation is a leader in Europe in the field of CNS technologies for air traffic management.

In aeronautical communications, DLR carries out research and development work in the field of ground-based and satellite-based communications, as well as for direct communication between aircraft. DLR has developed the physical layer for the future digital aeronautical radio LDACS within the framework of EUROCONTROL contracts and has played a major role in shaping the LDACS specification. Further development and detailed evaluation of LDACS under various application conditions - in particular realistic interference scenarios in the L-band - based on the specification was and is a further focus of DLR's work. This also includes the development of deployment strategies that allow LDACS to be introduced in the L-band in such a way that the CNS systems present there are not disturbed. The approach to add a navigation and airspace surveillance component to LDACS was also initiated and led by DLR. In addition, DLR has validated LDACS several times in flight tests.

Standardization

Within the framework of EUROCAE, two important standardization documents are being produced that contain detailed information on the equipment implementation of LDACS. These documents are the Minimum Aviation System Performance Standards (MASPS) and the Minimum Operational Performance Standards (MOPS). Both standardization documents assist equipment developers, manufacturers, service providers, and users in the implementation and deployment of LDACS. Furthermore, MASPS and MOPS regulate equipment requirements and characteristics as well as uniform test regulations.

In parallel to the EUROCAE activities, the standardization of LDACS is underway within ICAO. Since December 2016, the LDACS standardization group "Project Team Terrestrial Data Link" of the Communications Panel has been developing the so-called SARPs (Standards and Recommended Practices). The LDACS SARPs will be included in Annex 10 to the Chicago Convention (Convention on International Civil Aviation) after completion of the ICAO standardization and will thus become globally binding rules for air traffic. In addition to the SARPs, ICAO also produces guidance material to inform and support the ICAO standardization process and clarifies ICAO's internal allocation of frequency bands.

Flight test in SESAR project FALCO

In July 2022, flight tests to validate LDACS were carried out as part of the European ATM modernization initiative SESAR with the FALCO project. For this purpose, an LDACS aircraft radio was installed in DLR's Falcon research aircraft and two LDACS ground stations were set up and networked at DLR's Oberpfaffenhofen site. The focus in the FALCO project was on demonstrating end-to-end connectivity and validating LDACS mobility between different ground stations. Real aeronautical applications were used for this purpose, such as Controller-Pilot Data Link Communications (CPDLC) transmitted via the Aeronautical Telecommunications Network (ATN)/Internet Protocol Suite (IPS) protocol. In addition, during the ongoing data transmission, the LDACS data link was switched back and forth between the two ground stations, which had no impact on the end applications. This was the first time the "seamless handover" concept was demonstrated and the transparency property of LDACS was shown. The aeronautical applications were also transmitted using Datagram Transport Layer Security (DTLS), which establishes a secure tunnel between the endpoints of the communication. This also validated LDACS' ability to easily incorporate modern security measures. Other experiments during the flight tests included the sustained transmission of synthetic traffic, consisting of many small and some large data packets, as well as real and synthetic Automatic Dependent Surveillance - Contract (ADS-C) data. The synthetic traffic demonstrated reliable data transmission over several hours, while the ADS-C application demonstrated the ability of LDACS to reliably provide surveillance data.

Flight test in MICONAV project

The first LDACS flight tests were already carried out in spring 2019 in the MICONAV project, which was supported by the German Aeronautics Research Program (LuFo). In MICONAV, flight tests were conducted with an LDACS aircraft radio in DLR's Falcon research aircraft and a total of four LDACS ground stations. Two of the ground stations were full LDACS ground stations, and the other two ground stations were LDACS-only transmit stations necessary to validate the navigation functionality of LDACS. The focus of these flight tests was to validate the technical capabilities of LDACS, such as message prioritization, range, latencies, data throughput, and some cybersecurity characteristics. Furthermore, the total of four LDACS ground stations were used to validate the position determination in the aircraft using LDACS. Another important result of the flight tests was the proof that a cyber-secure Ground-Based Augmentation System (GBAS) can be realized with LDACS. GBAS improves the accuracy of satellite navigation systems by transmitting correction data to the aircraft. The improved position accuracy allows fully automatic landings and thus also landings under extreme visibility conditions.

The Team of the Research Group „Aeronautical Communications“

The LDACS flight tests in the FALCO and MICONAV projects were conducted in Dr. Michael Schnell's „Aeronautical Communications research group“.

• Dr. Schnell has been working on the development of LDACS since the beginning and leads the standardization activities on LDACS within ICAO.
• Dr. Thomas Gräupl was the project manager of FALCO.
• Nils Mäurer is a computer scientist and has developed the cybersecurity architecture for LDACS. Likewise, he shows responsibility for the security concept of cybersecure GBAS over LDACS.
• Leonardus Jansen is also a computer scientist and specializes in aircraft-to-aircraft communication security.
• Daniel Mielke is an electrical and information technology engineer developing an advanced data link for unmanned aerial systems called CDACS. In the FALCO project he was responsible for networking as well as building and operating the infrastructure. Furthermore, he developed the evaluation software for the physical layer of the LDACS data link.
• Miguel Bellido-Manganell is an electrical engineer and leads the extension of LDACS to aircraft-to-aircraft communications. For the flight tests, one of his tasks was to ensure compatibility with the other aeronautical systems through his frequency planning.
• Dr. Alexandra Filip-Dhaubhadel is an electrical engineer who develops surveillance concepts based on LDACS. She has used the flight tests to test new LDACS-based surveillance concepts.
• Ayten Gürbüz is an electrical engineer working on multi-antenna systems for LDACS air-to-ground communications.
• As an electrical engineer, Lukas Schalk is working in the aeronautical group on cooperative surveillance of drones based on direct communication between drones and has been instrumental in setting up as well as testing the experimental LDACS receive and transmit stations for the flight campaign.
• As the main person responsible for the hardware assembly of the flight campaign, Dennis Becker coordinated the assembly as well as supported the subsequent testing. As part of his scientific work, the electrical engineer is analyzing the specific signal propagation conditions for direct drone-to-drone communication in urban areas in order to avoid collisions between drones in the future with the help of robust and adapted communication systems.