The Ground Based Augmentation System (GBAS) is the cornerstone for enabling automated landings without the Instrument Landing System (ILS). Currently GBAS is evolving to GAST-D for CAT III landings. This extends GBAS via the use of multiple frequencies (L1/L2 and L5) and the use of multiple global navigation satellite system constellations. GBAS requires correction data to be broadcast to aircraft. This is currently done with the VHF Data Broadcast (VDB) datalink. However, VDB has several known shortcomings: (1) low throughput, (2) small area of operation and (3) no cyber-security measures. In this paper we propose the use of the L-band Digital Aeronautical Communications System (LDACS) for broadcasting GBAS correction data to address these shortcomings. In flight experiments conducted in 2019, we set up an experimental GBAS installation using LDACS. Broadcast data was secured using the TESLA broadcast authentication protocol. Our results indicate that cryptographically secured GBAS data via LDACS can provide GAST-C and GAST-D services with high availability if cryptographic parameters are chosen appropriately.

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The L-band Digital Aeronautical Communications System (LDACS) is a key enabler of the new air traffic services and operational concepts necessary for the modernization of the air traffic management (ATM). After its initial design, compatibility tests with legacy L-band systems, and functional demonstrations in the laboratory, the system is currently undergoing the standardization process of the International Civil Aviation Organization (ICAO). However, LDACS has not been demonstrated in flight yet. In this paper, we present the first in-flight demonstration of LDACS, which took place in March and April 2019 in southern Germany and included four LDACS ground stations and one LDACS airborne station. We detail the experimental setup of the implemented LDACS ground and airborne stations together with the flight routes, the conducted experiments, and the frequency planning to ensure compatibility with legacy systems. In addition, we describe the demonstrated ATM applications and the security measures used to protect them. Based on the obtained measurement results, we evaluate the LDACS in-flight communication performance for the first time, including the achieved communication range, the measured end-to-end message latency, and the LDACS capability to provide quality of service by effectively prioritizing safety-relevant data traffic. Furthermore, we use the in-flight received signal power to assess the applicability of a theoretical path loss model. These flight trials contribute to the final steps in the development of LDACS by providing its in-flight communication performance and by demonstrating: first, its correct functionality in a realistic environment; second, its capability of supporting ATM applications and the advanced security measures that can be used to protect them; and third, its spectrum compatibility with legacy systems. We conclude that LDACS is ready to support ATM operations and that LDACS frequency planning can safeguard legacy systems successfully.

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Growth of civil air traffic worldwide poses a great challenge for the supporting Communication, Navigation and Surveillance (CNS) infrastructure. Analogue systems have to be replaced by digital means to optimize spectrum efficiency and automation is becoming much more important to be able to handle the amount of participants in the air traffic system. As safety and security are strongly intertwined in aviation, cybersecurity is one key enabler for digitalization in civil aviation. As such we investigate mutual authentication and key agreement methods for the digital aeronautical ground-based communications system L-band Digital Aeronautical Communication System (LDACS). Thereby, we compare the suitability of three different Diffie-Hellmann (DH) key exchange flavors used in a modified version of the Station-To-Station (STS) protocol, for digital aeronautical communication in terms of latency and security data overhead. We conclude, the STS protocol based on a central Public Key Infrastructure (PKI) trust solution with Supersingular Isogeny Diffie-Hellman (SIDH) for post-quantum security to be best suited for long term security. However, due to the smaller key sizes, Elliptic Curve Diffie-Hellman (ECDH) is the more resource efficient candidate and may play a role in low resource authentication scenarios for LDACS.