GPS Accuracy Versus Number of NIMA Stations

C.H. Yinger, W.A. Feess, V. Nuth, R.N. Haddad

Abstract:	The current GPS ground system uses five worldwide Air Force monitor stations to collect ranging data for GPS satellite clock and ephemeris estimation. Current upgrades call for the inclusion of data from six core National Imagery and Mapping Agency (NIMA) stations in ground processing as part of the Accuracy Improvement Initiative/Architecture Evolution Plan (AII/AEP). Previous analysis showed that these core NIMA stations will improve GPS accuracy by about 10% for typical broadcast users and improve filter performance (at zero-ageof- data) by as much as 40%. This paper addresses the potential benefits of adding five more NIMA stations beyond the six core stations to the GPS ground system. The analysis shows that filter performance will improve up to 20% more due to the five additional NIMA stations. The typical broadcast user will initially gain only about 3% additional GPS accuracy improvement since broadcast accuracy is currently driven by clock prediction error. Improved earth orientation parameters, better satellite clocks, and reduced navigation message age-of-data all enhance GPS performance. The benefit of the five additional NIMA stations to the broadcast user approaches 15% if the navigation message update capability is implemented. Adding NIMA stations also improves satellite-monitoring capability that is critical for timely, robust integrity determination. Since the AII/AEP software is already designed to handle up to 20 stations, the use of five more NIMA stations requires only the addition of dedicated communication lines, so significant accuracy and integrity improvements can be achieved at relatively low cost.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	1526 - 1533
Cite this article:	Yinger, C.H., Feess, W.A., Nuth, V., Haddad, R.N., "GPS Accuracy Versus Number of NIMA Stations," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 1526-1533.
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