Improving Geostationary Satellite GPS Positioning Error Using Dynamic Two-Way Time Transfer Measurements

Benjamin Dainty, John Raquet, and Richard Beckman

Abstract:	GPS signals can be used for positioning satellites in geostationary (GEO) orbits, but the performance in this case is poor, because very few pseudorange measurements are available at any given time. This paper describes a new method for improving geostationary satellite navigation accuracy by using dynamic Two-Way Time Transfer (TWTT) measurements. By directly measuring the clock error between the GPS satellite and the GPS receiver, TWTT allows meaningful information to be gathered when less than four GPS satellites are available. A simulation was developed in which satellites in GEO orbits with GPS receivers onboard generated a position with 1) GPS with a crystal clock, 2) GPS with an onboard atomic clock, 3) GPS with TWTT to a ground-based atomic clock, and 4) GPS with TWTT to a ground-based clock synchronized to GPS time. Bringing an atomic clock into the system (Cases 2 and 3) resulted in a 21-38% improvement in the 3-D RMS position accuracy over the standard GPS case (Case 1). However, using TWTT with a clocked slaved to GPS time resulted in a 60%-70% improvement in 3-D RMS positioning accuracy. This level of performance was obtained for TWTT measurement error standard deviations anywhere between 0.3 ns to 30 ns.
Published in:	Proceedings of the 39th Annual Precise Time and Time Interval Meeting November 27 - 29, 2007 Hyatt Regency Long Beach Long Beach, California
Pages:	511 - 530
Cite this article:	Dainty, Benjamin, Raquet, John, Beckman, Richard, "Improving Geostationary Satellite GPS Positioning Error Using Dynamic Two-Way Time Transfer Measurements," Proceedings of the 39th Annual Precise Time and Time Interval Meeting, Long Beach, California, November 2007, pp. 511-530.
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