SATZAP: A Novel Approach to GPS Integrity

Karl Kovach, Rob Conley

Abstract:	Integrity continues to be a major issue preventing complete user acceptance of the Navstar Global Positioning System (GPS). The concerns about the integrity issue are being felt most severely in those applications where GPS has been proposed for use as an airborne navigation system. Substantial effort has therefore been invested by many interested parties in the pursuit of Failure Detection and Warning System (FDWS)concepts to improve upon the existing integrity of the GPS positioning services. Notable progress has been made towards developing FDWS approaches such as an independent GPS Integrity Monitoring Channel(GIC), Receiver Autonomous Integrity Monitoring (RAIM), and the integration of GPS with other navigation sensors. This paper presents the conceptual outline of a new FDWS to add to this list. The new FDWS that we are proposing is called "SATZAP". It is a novel approach that takes maximum advantage of existing GPS resources. It utilizes the Operational Control System (OCS) and on-orbit Block II Space Vehicles (SVs) already designed and built by the DOD. Its user notification method is unique amongst FDWSs. Failed SVs will simply be turned "off" as far as the user is concerned. Turning an SV "off" within the integrity time limit is inherently compatible with all types of GPS receiver equipment; absolutely no user modifications are required and the failure warning method cannot be misinterpreted. If fully implemented, SATZAP has the potential to provide alevelofintagrity assurance approaching VOR/DME equivalence on a global basis. The SATZAP conceptdescribedin this paper relies on a set of three recently developed techniques that overcome three of the most difficult problems encountered by GPS FDWSs. These are the problems of detecting that a failure has occurred, determining the seriousness of the failure,and warning the GPS user about the failure's effect -- all done within the allowable time budget of 10 seconds required for some airborne applications. These techniques are potentially applicable to other GIC-type integrity monitoring systems as well as to SATZAP.
Published in:	Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990) September 19 - 21, 1990 The Broadmoor Hotel Colorado Spring, CO
Pages:	387 - 396
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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