Use of Two-Way Time Transfer Measurements to Improve Geostationary Satellite Navigation

Capt Benjamin Dainty, John F. Raquet, Capt 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 effectively removing 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 positioning accuracy.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	2401 - 2411
Cite this article:	Dainty, Capt Benjamin, Raquet, John F., Beckman, Capt Richard, "Use of Two-Way Time Transfer Measurements to Improve Geostationary Satellite Navigation," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 2401-2411.
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