Galileo Mission Segment Processing Chain: Algorithm Design, Performance and Verification

C. Bourga, S. Lannelongue, F. Bauer, H. Delfour, M. van den Bossche, B. Lobert

Abstract:	Galileo is a European initiative to build a Global Navigation Satellite System that will offer high quality satellite positioning services with adequate guarantees and high availability. Galileo will provide worldwide satellite navigation and timing services to mass-market, professional, safety-of-life, and security-related users. Galileo will be interoperable with other systems, such as GPS, and it is open to international cooperation with navigation, timing, geodetic, and Search and Rescue communities. The system architecture includes a user segment, a space segment, and a ground segment made of a system control and a mission control part (Galileo Mission Segment - GMS). The GMS generates and uplinks all the data to be broadcast to the users, and controls all the related facilities. The functional Processing Chain includes the major Galileo system algorithms and is thus at the core of system performance. The main elements of GMS Processing Chain are: - 40 GSSs (Galileo Sensor Stations) - OSPF (Orbit & Synchronization Processing Facility) - IPF (Integrity Processing Facility) - MSF (Mission Support Facility) and its main algorithmic component, OAT (On-line Analysis Tool). The GSS measurements are continuously transmitted to OSPF and there processed to generate every 10 minutes ephemeris and clock navigation messages for uplink to and broadcast from all satellites. The messages also include a ionospheric model (based on NeQuick model) and Broadcast Group Delay, to be used by single frequency users. The GSS measurements are also processed for integrity purpose. The Galileo integrity concept is based on the following process: - OSPF estimation of the parameter that overbounds the Signal-in-Space Error (SISE) in a distribution sense, called Signal-in-Space Accuracy (SISA); - IPF estimation of its capability to monitor the SISE: SISMA (Signal In Space Monitoring Accuracy); similarly to SISA, this is the parameter that overbounds the error on IPFestimated SISE in a distribution sense; - transmission of the SISA and the SISMA within the navigation message, to allow the users to compute the Integrity Protection Levels; - real-time estimation of the SISE by the Integrity Processing Facility (IPF) and comparison with a threshold based on false alarm requirement; - based on the comparison, IPF real-time generation of integrity alerts when the IPFestimated SISE and the SISA are not consistent. SISA and SISMA are parameters that are specified with very stringent confidence levels. To achieve this performance, off-line processes are implemented in OAT to determine long-term statistics of SISE (HSISA, for Historical SISA) and IPF estimation errors (PREC, for Pre-Processing Ranging Error).
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	520 - 530
Cite this article:	Bourga, C., Lannelongue, S., Bauer, F., Delfour, H., Bossche, M. van den, Lobert, B., "Galileo Mission Segment Processing Chain: Algorithm Design, Performance and Verification," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 520-530.
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