GNSS/Galileo Global and Regional Integrity Performance Analysis

Helmut Blomenhofer, Walter Ehret, Arian Leonard and Eduarda Blomenhofer

Abstract:	Augmented GPS and Galileo are expected to serve as navigation sources for a variety of applications. The most stringent performance requirements are derived from safety critical applications including aviation precision approach operations. Where GPS integrity is determined by augmentation systems like WAAS or EGNOS the Galileo baseline architecture specifies a global integrity concept. This means e.g. that the accuracy and integrity performance must be achieved globally keeping the Time-To-Alert thresholds. Further major performance measures are the availability of the Accuracy and Integrity figures and the Continuity of Service. The GPS augmentation systems provide besides the wide area differential corrections also related residual errors which are used to compute Protection Levels. This is done in near real-time with latency times of maximum 6 seconds (UDRE concept), which grants a timely warning if failures in the GPS system occur. The Galileo concept uses a combination of predicted errors (caused by satellite, clock, and non-precise navigation message) which are validated in real-time by integrity monitoring taking into consideration the monitoring accuracy. The latter is considered by a new introduced parameter, the SISMA (SIS Monitored Accuracy) The predicted component which is transmitted with the navigation message is called SISA (Signal In Space Accuracy) and is a quantitative estimation of the orbit and clock prediction of the Galileo Control Centre. SISA is updated with every clock correction update in the Navigation Message (Ephemeris Set). The two parameters SISA and SISMA will be used by the user to compute a Protection Level associated to the positioning result. If an error occurs in the satellites, clocks, signal, navigation message or in the processing itself, then it has to be detected by the Integrity Processing Facility (IPF) in real-time and a warning flag IF has to be raised. This leads to the exclusion of the related (Faulty) satellite from both, the positioning equations and from Protection level equations. In the Galileo Global concept there will be a global monitoring network. However Regions will be given the possibility to built up there own regional Monitoring and Integrity Determination Network. Previous assessments and analysis have demonstrated the integrity performance potential of the Galileo global Integrity concept using simplified Service Volume Simulations (SVS). This paper shows the results determined by more sophisticated SVS using e.g. inclusion of operational outages as well as the consideration of the critical satellite concept. The SISMA driven performance is analysed for the Global and an exemplary Regional case. The achievable Integrity performance is then mapped to the aviation performance standards as currently discussed by the ICAO. Finally a trade-off will be performed on the basis of previously introduced results for the other Integrity concepts like RAIM for combined GNSS systems or space based augmented GPS.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	2158 - 2168
Cite this article:	Blomenhofer, Helmut, Ehret, Walter, Leonard, Arian, Blomenhofer, Eduarda, "GNSS/Galileo Global and Regional Integrity Performance Analysis," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 2158-2168.
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