GPS Time Transfer Precision and Accuracy

B. Feess, B. Winn

Abstract:	The Global Positioning System (GPS) delivers time. Users of the GPS employ the differential arrival of satellite-timed broadcasts to effect navigation and to determine UTC (USNO), GPS time, and user network synchronizations. To effect a controlled 10-week demonstration (February 1, 1987 through April 19, 1987) of the GPS time transfer precision (consistency over geometry and time), pseudorange measurements acquired by the five GPS monitor stations were processed using satellite broadcast ephemerides and clock phases. As control, pseudorange from three DMA monitor stations for the same 10-week period were processed separately. Both networks used dual-frequency P-code receivers (99 percent ionospheric calibration) and DMA location surveys (1 m horizontal rms error, 1.5 m vertical rms error). Using pseudorange received by the monitor stations in each week, least squares estimates of the average phase and frequency of each monitor station clock over the 7 days were made and removed from the satellite-to-monitor station pseudorange. Although the rms pseudo­range fit residual is below 15 ns, the residuals to the fits are not white: Time-correlated pseudorange residuals with peak-to-peak amplitudes of up to 30 ns are observed. Such residuals are most likely indicative of a GPS modelling error. Analyses by the authors and others suggest that the prototype NAVSTAR 3 and 6 satellites (Block I) have rubidium clocks that are being frequency tuned by satellite temperature changes. Other modelling error(s) might also be present.
Published in:	Proceedings of the International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1988) September 19 - 23, 1988 The Broadmoor Hotel Colorado Spring, CO
Pages:	469 - 485
Cite this article:	Feess, B., Winn, B., "GPS Time Transfer Precision and Accuracy," Proceedings of the International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1988), Colorado Spring, CO, September 1988, pp. 469-485.
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