Broadcast vs Precise GPS Ephemerides: A Historical Perspective

David L.M. Warren and John F. Raquet

Abstract:	The Navstar Global Positioning System (GPS) Operational Control Segment (OCS) generates predicted satellite ephemerides and clock corrections that are broadcast in the navigation message and used by receivers to estimate real-time satellite position and clock corrections for use in navigation solutions. Any errors in these ephemerides will directly impact the accuracy of GPS based positioning. This paper compares the satellite position computed using broadcast ephemeredes with the precise position provided by the International GPS Service for Geodynamics (IGS) Final Orbit solution. Similar comparisons have been undertaken in the past, but for only short periods of time. This paper presents an analysis of the GPS broadcast ephemeris position error on a daily basis over the entire operational lifetime of the GPS system. The comparison was undertaken from 14 Nov 93 through to 1 Nov 01. The statistics of these errors were also analysed. In addition, the satellite position computed using the almanac ephemeris was compared to the IGS precise final orbit to determine the long-term effect of using older almanac data.
Published in:	Proceedings of the 2002 National Technical Meeting of The Institute of Navigation January 28 - 30, 2002 The Catamaran Resort Hotel San Diego, CA
Pages:	733 - 741
Cite this article:	Warren, David L.M., Raquet, John F., "Broadcast vs Precise GPS Ephemerides: A Historical Perspective," Proceedings of the 2002 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2002, pp. 733-741.
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