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Session B3: Future Trends in GNSS Augmentation Systems

Development of the H-ARAIM/FDE Capability for an Aviation Receiver Prototype
Denis Bouvet, Frederic Chauveau, Bernadette Couteiro, Gregoire Jacotot, Thales AVS France
Date/Time: Thursday, Sep. 22, 9:43 a.m.

In the frame of the EDG2E (Equipment for Dual frequency Galileo GPS and EGNOS) project, funded by the European Union Agency for the Space Programme (EUSPA), Thales AVS is developing a GPS / Galileo Dual Frequency SBAS L5 prototype receiver. This prototype embeds an H-ARAIM/FDE capability based on the ARAIM Algorithm Definition Document ADD v3.1 [1], complemented by the temporal effects detailed in [2], that have since been introduced in the fourth version of the ADD and that are summarized in [3].
With respect to the Receiver Autonomous Integrity Monitoring (RAIM) class of algorithms that relies on a static definition of the probabilities of failure of the GPS constellation, the Horizontal Advanced RAIM (H-ARAIM) capability in airborne equipment is meant to provide integrity to a navigation solution using signals from GPS and other GNSS core constellations, with probabilities of failure provided to the receiver through Integrity Support Messages (ISM) broadcast in the signal in space, or with fixed default values corresponding to the integrity commitments published by the constellation service providers.
The first objective of the paper is to present step by step, from the determination of the faults to be monitored, to the calculation of the protection levels, the design choices made to limit computational load. A key-contributor being the designation of the faults to be monitored, the implemented H-ARAIM/FDE capability relies on the minimum integrity performance to be published in the ICAO SARPs to further reduce the number of fault modes monitored by the fixed subset selection scheme proposed in [4], while maintaining the probability of non-monitored faults at an acceptable level. Another major contributor to the computation load is the computation by itself of the protection levels. Here, the baseline iterative method is modified to speed up the convergence to the protection level value and to limit the number of calls to the error function.
The resulting computational reductions are then quantified offline and the performance of the H-ARAIM prototype is compared to the reference algorithm, based on availability simulations with representative assumptions for GPS and Galileo constellations.
The paper will then present the results obtained with the software executed on a hardware platform representative of the airborne equipment, including test procedure results (detection and exclusion) and computational load assessment.
The conclusions of the paper will discuss the limitations of the current prototype, and the activities needed for consolidating the implementation of the H-ARAIM/FDE capability in future multi-constellation airborne equipment.
[1] WG-C Advanced RAIM Technical Subgroup, "Reference Airborne Algorithm Description Document Version 3.1," 2019.
[2] C. Milner, B. Pervan, J. Blanch and M. Joerger, "Evaluating Integrity and Continuity Over Time in Advanced RAIM," in 2020 IEEE/ION Position, Location and Navigation Symposium (PLANS), Portland (Oregon), 2020.
[3] J. Blanch, T. Walter, C. Milner, M. Joerger, B. Pervan and D. Bouvet, "Baseline Advanced RAIM User Algorithm: Proposed Updates," in Proceedings of the 2022 International Technical Meeting of The Institute of Navigation, Long Beach, California, 2022.
[4] J. Blanch, T. Walter and P. Enge, “Fixed Subset Selection to Reduce Advanced RAIM Complexity,” in Proceedings of the 2018 International Technical Meeting of The Institute of Navigation, Reston, Virginia, 2018.



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