EGNOS Protection on Two GPS Clock Events

Jean Maréchal, Norbert Suard and David Chinchilla

Abstract:	EGNOS, the European Geostationary Navigation Overlay Service, has been in Initial Operation Phase since August 2005. During this phase the system has been operated nominally and provides GPS augmentation messages to European users. EGNOS augmentation does not only transmit ionosphere and GPS clock and orbit corrections but also protection information for the ‘safety of life’ users. This protection meets aeronautical integrity (horizontal and vertical protections, time to alarm) and continuity requirements. This paper presents the protection, which was provided by EGNOS during two recent GPS clock events when satellites were in view of Europe. After these events, the GPS users get a notice (NANU) from the GPS ground segment. Analysis of these events starts by observing GPS satellites behaviour. Clock models, user range accuracy and the healthy flag that were broadcast in GPS navigation messages during the events are presented and analysed. This analysis covers the event period and it’s evolution up to return to normal service. Links with related NANUs are done. During the events, the real satellite’s clock behaviour is estimated based on IGS products. This gives an estimation of the clock errors, which are compared to impacts observed at user level. These impacts on users are evaluated at several European locations. Horizontal and vertical errors in position are exposed. The status of the EGNOS system during the events is then presented. The EGNOS corrections that were broadcast in signal in space to European users during the events are described and explained. Compliance with SBAS recommendations and EGNOS system requirements is assessed at signal in space level. Then integrity at user level is checked at the same locations. Conclusion is that EGNOS users were fully protected during both events. EGNOS system fully met its SBAS requirements, providing the expected integrity to safety of life users.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	919 - 926
Cite this article:	Maréchal, Jean, Suard, Norbert, Chinchilla, David, "EGNOS Protection on Two GPS Clock Events," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 919-926.
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