Flight Trial Demonstration of Secure GBAS via the L-band Digital Aeronautical Communications System (LDACS)

Abstract

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.

Performance-Optimizing Secure GBAS Over LDACS

“…GBAS over LDACS was first demonstrated in the MICONAV project as reported by Mäurer et al [12] and Bellido et al [3]. The main purpose of the GBAS over LDACS experiment was to demonstrate the ability of LDACS to provide a secure, broadband datalink for GBAS.…”

“…The TESLA protocol has several requirements to work: Sender and receivers have to be loosely time synchronized; they have to have previously agreed upon key derivation, MAC tag generation, and verification algorithms; and every new participant has to receive the TESLA parameters in an authentic manner. [13] Analysis of Mäurer's results [12] indicated that the configuration of the TESLA protocol has a profound impact on the overall performance of secure GBAS over LDACS. The main TESLA parameters, that are relevant in the context of this paper are: the interval time T int , the key disclosure delay d, and the key k i for generating a MAC of a message m to be sent in interval i.…”

“…Mäurer et al [12] presented two measurement results for the communication latency of secure GBAS over LDACS. The results are displayed in Fig.…”

“…As of now, this datalink is specific to GBAS: The VHF Data Broadcast (VDB). [12] The VDB datalink has been identified as potentially limiting the evolution of GBAS: Lee et al have critized that VDB can only transmit corrections for the L1 frequency of GPS satellites, which may be problematic in terms of availability in equatorial zones [11]. Feuerle et al and Stanisak et al have noted that VDB does not provide sufficient throughput for correction and integrity data for multiple constellations and frequencies [8], [16].…”

“…This lead Felux et al to propose the use of an alternative datalink for GBAS [9]: The L-band Digital Aeronautical Communication System (LDACS), which is a general purpose broadband datalink for aeronautical communication related to safety and regularity of flight [15]. [12]. The results demonstrated the general feasibility of GBAS over LDACS.…”