A New System Level Integrity Concept for Galileo: The Signal In Space Accuracy

Esperanza Herraiz-Monseco, Alvaro Mozo Garcia, Miguel M. Romay Merino and Ana Belen Martin Peiro

Abstract:	In the future a Global Navigation Satellite System, like Galileo, will not only provide positioning and timing services, but it may also provide integrity service. The integrity risk can be defined as the probability during the operation period that an error, whatever its source, might result in a computed position error exceeding a maximum allowed value (called the Alarm Limit), and the user would not be informed within the specific time to alarm. The integrity service will be linked to the specific service to be provided, and therefore to the users. Integrity requirements will be different for each individual application and therefore it would be very difficult to fulfil all integrity requirements with a common technique. The provision of integrity, and in particular the time to alarm, is a critical design factor having an enormous impact on the complexity and total cost of the system. Satellite ephemeris and clock errors are major contributors to the total user positioning error. The latest improvements in the precise orbit determination techniques as well as the high quality (predictability) of the on-board clocks are opening new possibilities for obtaining accurate ephemeris and clock predictions. At the Galileo Orbitography and Synchronisation Processing Facility (OSPF), where accurate orbits and clocks are computed, a prediction of the Signal In Space Accuracy (SISA) can be computed. This prediction is expected to be accurate over relatively long time periods, and will provide to the users an indication of the ephemeris and satellite clock errors. The main advantage of the SISA is that it does not increase the system cost as it is computed using the outputs of the orbit determination and time synchronisation process. It should be considered that the SISA would not provide bounds for effects like multi-path, thermal noise, ionosphere, troposphere and other local effects. Therefore RAIM (Receiver Autonomous Integrity Monitoring) techniques would constitute a very valuable complement to the SISA.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	1304 - 1316
Cite this article:	Herraiz-Monseco, Esperanza, Garcia, Alvaro Mozo, Merino, Miguel M. Romay, Peiro, Ana Belen Martin, "A New System Level Integrity Concept for Galileo: The Signal In Space Accuracy," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 1304-1316.
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