Sensitivity Analysis of the Galileo Integrity Performance Dependent on the Ground Sensor Station Network

Helmut Blomenhofer, Walter Ehret, Hua Su and Eduarda Blomenhoter

Abstract:	The European Satellite Navigation System Galileo which is currently under development offers a number of services. The Galileo Safety Of Life (SOL) service is intended for use with safety critical applications, particularly in the transportation sector. The SOL service provides standard PVT (Position Velocity Time) to the users combined with an integrity information service. This service will be provided on a global scale. The SOL service will broadcast safety related information in form of several parameters. One of these parameters is the SISA - the Signal In Space (SIS) Accuracy, which is broadcast and assigned to each Ephemeris broadcast. SISA shall be a bound for the true SIS Errors with definite probability and is determined in the Galileo Control Center which determines the Orbit&Clock parameters. The SISA in itself as a predicted parameter (for up to 100 minutes) will be validated in real time using observations of a global network of Monitoring Sites. These Galileo Sensor Stations (GSS) are a fundamental part of the Galileo Ground Segment. In the final deployed System the number of GSS is in the order of thirty to forty units. The GSS Network Geometry will influence the observability of the SISE, the so called SISMA (SIS Monitoring Accuracy) parameter, which is also broadcast regularly within the SOL data frames. Finally with the determination of SISE the SISA can be evaluated and broadcast using the Integrity Flags which are determined by the Integrity Determination Process in the Galileo Ground Mission Segment. This paper describes the work and preliminary results to analyse the sensitivity of the Galileo SOL performance to the GSS network. The new proposed Galileo Integrity concept which was published by ESA/GaIn was implemented in an advanced Service Volume Simulator. Depth of Coverage for the Galileo satellites and SISMA coverage are calculated for assumed variations of the number and distribution of the GSS global network. Finally the Integrity Risks are calculated on a global scale and for different time frames. Special attention is drawn to the required Availability figures as referenced in Galileo System requirements for SOL services (different levels) and mapped to the Aviation standards as published by ICAO SARPS for GNSS Radio-Navigation services. The present work will outline the performance of the Galileo Integrity determination and the sensitivity to Sensor Station outages. The results will demonstrate how the performances of Galileo SOL service can vary with place and time, compared with the guaranteed or specified performances.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1361 - 1373
Cite this article:	Blomenhofer, Helmut, Ehret, Walter, Su, Hua, Blomenhoter, Eduarda, "Sensitivity Analysis of the Galileo Integrity Performance Dependent on the Ground Sensor Station Network," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 1361-1373.
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