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Session B3: Future Trends in GNSS Augmentation Systems

Galileo H-ARAIM: Update on Performance Characterization and Integrity Support Message
S. Perea, S. Wallner, European Space Agency; M. Schoenfeldt, K. Binder, M. Odriozola, Airbus Defense and Space GmbH, Munich; A. Donatelli, E. Foucault, C. Stallo, Thales Alenia Space; M. Sgammini, I. Martini, J.P. Boyero, European Commission; M. Mabilleau, E. Canestri, N. Castrillo European Union Agency for Space Programme
Date/Time: Thursday, Sep. 22, 9:20 a.m.

The modernization of GPS with a new generation of satellites, along with the development of the emerging Galileo constellation, provides already new navigation signals and frequencies that will enable for the provision of Advanced Receiver Autonomous Integrity Monitoring (ARAIM) capabilities. Based on measurement redundancy, ARAIM airborne algorithm performs consistency checks are able to detect and exclude ranging measurements coming from potentially faulty satellites. One distinctive aspect of ARAIM with respect to other GNSS augmentation systems is the on board fault monitoring at user level. In GNSS Safety-of-Life applications such as aircraft guidance, navigation safety is guaranteed based on whether or not integrity, continuity and accuracy requirements are met. In order for the users to evaluate those three performance metrics, inputs from ground need to be encapsulated in the so-called Integrity Support Message (ISM) [1].
In recent years, the constellation performance characterization has been a profuse topic in the GNSS literature with a particular focus on the SIS fault probability determination. Several GNSS performance characterization have been presented by Walter [2], Perea [3] and Montenbruck [4] in the past years. In parallel, diverse studies have been published in overbounding theory, satellite failure rate determination and ISM generation methods by Walter [5][6], Perea [7] and Martini [8]. Standardization bodies and civil aviation institutions have been intensively working on the ARAIM concept of operations (CONOPS) [9] and ARAIM is in the scope of the new Minimum Operational Performance Standards (MOPS) being developed by EUROCAE and RTCA [10]. This paper provides an update on the Galileo performance characterization conducted by the European Space Agency (ESA) supported by its industrial partners. Along this line, this paper introduces the latest deployments on the Galileo Integrity Support definition and standardization work carried out by the European Commission (EC) and the European Union Agency for the Space Programme (EUSPA)

The first part of the paper is dedicated to characterize the H-ARAIM performance of Galileo based on measurement data. In order to be able to contribute to ARAIM solutions, the core constellation has to demonstrate (among others) to be able to meet relevant performance metrics, related to Signal in Space Error (SISE) and its bounding. In case a SIS fault occurs in which the actual SISE error is exceeding a pre-defined threshold, the core constellation has to demonstrate that such events are sufficiently rare in terms of onset probability and in case of occurrence that these are detected within time. In order to characterize the ARAIM capabilities of Galileo the Integrity Failure Mode and Effect Analysis (IFMEA) is ongoing since December 2016 and more than 5 years of Galileo service history have been processed and have been evaluated regarding the key parameters for ARAIM, i.e. SISE distribution and the Probability of Satellite/Constellation faults (which are the product of the onset of a fault at single satellite level or at constellation level and the Mean Time to Notify (MTTN)).
After more than 5 years of Galileo in-service data a good picture of Galileo past performance can be drawn. This paper presents the latest results of the IFMEA process demonstrating how the constellation has exceeded its performance commitment ensuring the use of Galileo for H-ARAIM service. This paper will show that the as-observed performance in terms of narrow and wide fault state probability along with the User Range Accuracy (URA) already exceed the expected values for Galileo Full Operational Capability (FOC) as identified in [11], Annex D.6.
The second part of the paper is dedicated to the derivation of the ISM parameters from the perspective of an ISM Generator (ISMG). The ISMG is the entity responsible for the determination and validation of the Integrity Support Message transmitted by Galileo. In this paper, an exemplary implementation of a Galileo ISMG will be considered. The exemplary implementation is based on the ISMG architecture and methodologies developed in the project ARTEX of the European Commission. A description of the main methodologies of the ARTEX ISMG used for the derivation of the relevant integrity data (i.e. Psat, Pconst, URA, and bnom) was already provided in [12].
The methodologies include the generation of the SISE time series representative of the worst user location and its correct overbounding. The paper will present results on the temporal evolution of the ARAIM parameters over long time, through the processing of over 5 years of real Galileo data, collected since Galileo Initial Service Declaration. Finally, this paper provides an update on the initial design of the Galileo ISM message type originally presented in [13] based on those results.
REFERENCES
1. Working Group C, ARAIM Technical Subgroup, EU-US Cooperation in Satellite. Navigation, \Milestone 3 report," Tech. Rep., March 2016. https://ec.europa.eu/docsroom/documents/15641/attachments/1/translations/en/renditions/native
2. Walter et al. Characterization of GPS Clock and Ephemeris Errors to Support ARAIM, Presented April 2015 at the Institute of Navigation (ION) Positioning, Navigation and Timing Conference, Honolulu, Hawaii.
3. Perea et al. “URA/SISA Analysis for GPS and Galileoto Support ARAIM,”Navigation, Vol. 64, No. 2,Summer 2017, pp. 237-254
4. Montenbruck et al. Multi-GNSS signal-in-space range error assessment – Methodology and results Advances in Space Research. Volume 61, Issue 12, 15 June 2018, Pages 3020-3038
5. Walter et al. Validation of the Unfaulted Error Bounds for ARAIM. Published in NAVIGATION , Vol. 65, No. 1, Spring 2018, pp. 117-133, DOI 10.1002/navi.214.
6. Walter et el. "Determination of Fault Probabilities for ARAIM," in IEEE Transactions on Aerospace and Electronic Systems, vol. 55, no. 6, pp. 3505-3516, Dec. 2019, doi: 10.1109/TAES.2019.2909727.
7. Perea, S, Meurer, M, Pervan, B. Impact of sample correlation on SISRE overbound for ARAIM. NAVIGATION. 2020; 1– 16. https://doi.org/10.1002/navi.346
8. Martini, Ilaria, Sgammini, Matteo, "Integrity Support Message Generation Algorithm Prototype," Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019), Miami, Florida, September 2019, pp. 552-572.
9. Blanch et al. “Development of the ARAIM MOPS” Proceedings of the 32nd International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2019), Miami, Florida, September 2019
10. Blanch, Juan, Walter, Todd, Enge, Per, Burns, Jason, Mabilleau, Mikael, Martini, Ilaria, Boyero, Juan Pablo, Berz, Gerhard, "A Proposed Concept of Operations for Advanced Receiver Autonomous Integrity Monitoring," Proceedings of the 31st International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2018), Miami, Florida, September 2018, pp. 1084-1090.
11. European GNSS (Galileo) Open Service Definition Document, Issue 1.2, 11/2021
12. Martini, Ilaria, Sgammini, Matteo, Boyero, Juan Pablo, "Error Bounding for ARAIM Integrity Support Message Generation," Proceedings of the 33rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2020), September 2020, pp. 1068-1088. https://doi.org/10.33012/2020.17577
13. Wallner, Stefan, Perea, Santiago, Odriozola, Miguel, Brieden, Phillip, Binder, Kerstin, Nuckelt, A., Donatelli, Alessandro, Joly, Damien, Stallo, Cosimo, Sgammini, Matteo, Martini, Ilaria, Boyero, Juan Pablo, Mabilleau, Mikael, Canestri, Ettore, "Galileo H-ARAIM Characterization and Galileo Integrity Support Message (ISM)," Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021), St. Louis, Missouri, September 2021, pp. 1375-1391.



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