Transmitting GBAS messages via LDACS

Abstract

The Ground Based Augmentation System (GBAS) is a landing system for aircraft based on Global Navigation Satellite Systems (GNSS). It consists of a reference station at an airport that generates corrections and integrity parameters that are transmitted to arriving aircraft. The broadcast is currently accomplished via a VHF data broadcast (VDB). In recent years it turned out that proper siting and frequency planning for the VDB is a challenging task in an operational environment. Coverage, as well as signal power issues, especially at large and complex airports have led to a number of considerations that have to be taken into account when installing VDB transmission antennas. Furthermore, current GBAS only broadcast corrections for the L1 frequency of GPS satellites. Availability issues, mainly due to ionospheric effects in equatorial regions, however, drive the development of expanding GBAS from a single frequency single constellation system towards a dual frequency multi constellation architecture. Transmitting additional corrections and integrity parameters at the same update rate is challenging due to the limited capacity of the VDB data link. Finally, transmission should offer the potential to provide secure transmissions with an authenticated signal in order to be robust also from a security perspective. For all these reasons it can be envisioned to provide the GBAS messages via LDACS which is currently in the process of standardization. This could resolve the issues mentioned and thus support GBAS implementation in the future. This paper provides an overview of the expected benefits mentioned above and provides a first performance estimation of GBAS over LDACS.

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

“…Our experiments used a single GBAS ground receiver with limited ground monitoring, thus without ionosphere and ephemeris monitoring or B-value checks. However this has no influence on the purpose of the experiment, thus it characterizes GBAS over LDACS similar as proposed in [8].…”

“…Transmission of all data was combined in one correction/integrity message per epoch. Producing corrections for all visible satellites our experimental setup generated data rates as predicted in [8]: Approximately 3500 Byte/s, distributed over several communication packets per second. To allow for better characterization of LDACS performance each set of corrections (every 0.5 s) was sent twice with the redundant second message 0.2 s delayed.…”

“…The criticism is that for pilots to verify that the system is operational an increased range of GBAS services would reduce the pressure and stress level during the final approach. (3) Cyber resilience is also problematic with VDB, since it provides no cyber-security measures comparable to modern wireless systems [7,8].…”

LDACS Flight Trials: Demonstration and Performance Analysis of the Future Aeronautical Communications System

“…The audio messages had to be prerecorded due to the noisy environment of the test aircraft. Fourth, correction data from an experimental GBAS deployment at the German Aerospace Center (DLR) site in Oberpfaffenhofen [30] were collected by the GS-OP computer and sent to the AS computer using LDACS. Using the correction data provided in the GBAS messages, the aircraft can estimate its GNSS-based position much more accurately and with a higher integrity level, allowing it to perform complex ATM procedures not feasible otherwise [31].…”

Performance-Optimizing Secure GBAS Over LDACS

“…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]. Finally, Felux et al and Garcia et al have called attention to the issue that VDB does not provide cybersecurity measures on par with modern wireless systems [6], [9]. 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].…”