Independent URA Monitor With RAIM for LPV-200 Using GPS or/and Galileo

C.A. Shively, B. Bian, R. Braff, R. Conker, M. Bakry El-Arini

Abstract:	The User Range Accuracy (URA) parameter broadcast by each GPS satellite allows users to compute a bound on the fault-free and fault-induced errors in the signal-in-space from that satellite. This paper presents and analyzes a concept wherein an independent URA ground monitor (IUM) ensures bounding validity of the URA in conjunction with user Receiver Autonomous Integrity Monitoring (RAIM) to provide Localizer Performance with Vertical Guidance aircraft precision approach down to a decision height of 200 ft (LPV-200). RAIM is needed to mitigate satellite faults that may occur during the IUM notification delay. Minimum Monitorable URA (MMU) values are presented for GPS if monitored by 17 GPS ground stations and also for Galileo under the assumption it would be monitored in a similar fashion by its own 19 Initial Operational Capability (IOC) monitor stations or 30 Final Operational Capability (FOC) monitor stations. MMU performance depends to some extent on the value of URE which characterizes nominal fault-free satellite range error. Resulting MMU values (95th percentile world-wide) are predicted to be 2.1 m for GPS alone (URE = 0.25 m), and 6.2 m for Galileo (assuming URE = 0.7 m) with 19 IOC monitor stations or 0.66 m for Galileo with 30 FOC monitor stations. For Galileo assuming URE = 0.5 m, the 6.2 m result remains unchanged, but the 0.66 m result is reduced to 0.55 m. Availability of LPV-200 service using the MMU values is predicted considering simultaneously satisfying two fault-free and two faulted (integrity from RAIM) error bounding criteria. Availability results depend on both the MMU characterizing integrity and also the value of URE. LPV-200 coverage (% of area with at least 0.995 availability) is assessed for each constellation alone and GPS plus Galileo. For GPS alone, even with the smaller system URE = 0.25 m, the coverage over CONUS is only 16% and over the entire global land area is only 7.5%. For Galileo alone (assuming URE = 0.7 m) coverage over Europe is only 70% even using 30 FOC Galileo monitor stations. However, if Galileo URE = 0.5 m can be achieved, coverage over Europe is 89% with the 19 IOC Galileo monitor stations and would be 100% over the entire globe with the 30 FOC Galileo monitor stations. For GPS plus Galileo, even for Galileo URE = 0.7 m, coverage is 100% over CONUS, 100% over Europe and 98% of the globe for 19 IOC Galileo monitor stations and is 100% of the globe with 30 FOC Galileo monitor stations.
Published in:	Proceedings of the 2012 International Technical Meeting of The Institute of Navigation January 30 - 1, 2012 Marriott Newport Beach Hotel & Spa Newport Beach, CA
Pages:	1777 - 1817
Cite this article:	Shively, C.A., Bian, B., Braff, R., Conker, R., El-Arini, M. Bakry, "Independent URA Monitor With RAIM for LPV-200 Using GPS or/and Galileo," Proceedings of the 2012 International Technical Meeting of The Institute of Navigation, Newport Beach, CA, January 2012, pp. 1777-1817.
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