Comparison of Airborne Processing Modes for Dual-Frequency Multi-Constellation GBAS

David Duchet, Mirko Stanisak, Natali Caccioppoli, Pierre Ladoux, and Andreas Lipp

Abstract: This paper presents the comparison of different GBAS DFMC (dual-frequency/multi-constellation) processing modes using GPS L1/L5 and GALILEO E1/E5a data. For this study, data recorded at Toulouse airport in the frame of SESAR 2020 project 14-3-1 was used. Using dual-frequency modes offers several possibilities regarding position, time, and protection level processing. Two main solution groups are considered: either using both frequencies to obtain an ionosphere-free position solution, or keeping a mono-frequency position solution while using both frequencies to detect ionospheric anomalies. Aviation poses specific interoperability constraints in this context, as unlike in fields such as geodesy, dissimilar receivers are often used on the aircraft and ground respectively. The processing modes thus have to ensure similar treatment of both navigation and ranging data on ground and in the air, despite differences in geometry, navigation data, visibility durations and noise levels. The objective of this analysis is to determine the more suitable solutions to be used in the aeronautical navigation context in terms of accuracy and integrity. During this investigation, several tools were used in parallel to ensure algorithm validity via cross-checking: TriPos, a real-time differential navigation solution from the Institute of Flight Guidance at Technische Universität Braunschweig, and the Pegasus post-processing toolset from EUROCONTROL. It was necessary to implement algorithmic modifications to the airborne tools in order to take into account navigation data set group delay compensation in several processing modes, in particular the ionosphere-free mode using GPS L/NAV and GALILEO I/NAV navigation messages. Data used originates from the first DFMC flight test campaign conducted in the frame of SESAR research in summer 2016. The process involved several steps: First the applicable multipath requirement compliance of the reference receiver antennas have been verified in the SESAR 1 project 15.3.7 activities. Then the raw data of the Toulouse GBAS ground station reference receivers and the (static) airborne receiver have been collected in the manufacturer’s binary format in order to have all parameters necessary for post-processing available. As the third step, the recorded data of the reference receivers was processed by TriPos’ ground facility simulation to generate raw GBAS DFMC VDB messages. Finally, the position, time, and protection levels were computed using both airborne simulation tools. This process was repeated on different data sets covering several visibility periods in order to cope with the limited number of dual-frequency satellites currently available and provide a variety of constellation geometries. Evaluations have centred on the positioning performance of the simulated airborne users for the different novel GBAS services. For the ionosphere-free position processing, effectively mitigating most ionospheric threats, the accuracy and availability at short range is degraded with respect to single-frequency processing due to the increase in noise of the ionosphere-free combination on the one hand, and the low number of satellites providing valid L5 signals on the other hand. Furthermore, using single frequency positioning requires more conservative bounding at greater range, which might impact availability. This paper shows initial performance results of this kind of DFMC service. This paper summarizes the results obtained and provides recommendations for the selection of an appropriate processing mode.
Published in: Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018)
September 24 - 28, 2018
Hyatt Regency Miami
Miami, Florida
Pages: 1510 - 1522
Cite this article: Duchet, David, Stanisak, Mirko, Caccioppoli, Natali, Ladoux, Pierre, Lipp, Andreas, "Comparison of Airborne Processing Modes for Dual-Frequency Multi-Constellation GBAS," Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018), Miami, Florida, September 2018, pp. 1510-1522.
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