A Synergistic Solution To The GPS Integrity Problem

John W. Diesel

Abstract:	For safety in civil navigation, it is necessary to provide GPS integrity monitor (IM) warnings within seconds when out-of-tolerance conditions exist. Unlike VOR, which provides such warnings within six seconds, the existing GPS Operational Control System (OCS) may take hours. An alternative, called Receiver Autonomous Integrity Monitoring (RAIM), is to detect or isolate failures by using redundant satellite information, when available. However, the average availability of RAIM is inadequate for sole-means navigation, and is low even for supplementary navigation. It is shown that the existing GPS OCS can safely and reliably provlde integrity warnings within 30 minutes by setting health bits in the satellite. Present 2 nmi/hr commercial inertial systems have Random Walk Coefficients (RWC) of only 0.00125 deg.&q. rt. hr., one sigma. This makes it possible to coast pure inertial for 30 minutes without exceeding the 0.3 nmi PdRMS spec for non-precision approach, after calibration using GPS. By delaying the use of GPS data for calibration for 30 minutes, when the integrity is assured, the system can use only 4 satellites for sole means of navigation for coasting periods up to 30 minutes, and 5 satellites otherwise. This increases the availability to 99.8% for sole means of navigation in the non-precision approach phase, without using RAIM at all.
Published in:	Proceedings of the 1991 National Technical Meeting of The Institute of Navigation January 22 - 24, 1991 Sheraton San Marcos Hotel Phoenix, AZ
Pages:	229 - 236
Cite this article:	Diesel, John W., "A Synergistic Solution To The GPS Integrity Problem," Proceedings of the 1991 National Technical Meeting of The Institute of Navigation, Phoenix, AZ, January 1991, pp. 229-236.
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