An Alternative Common View Method for Time Transfer With GPS

H. F. Fliegel, R. L. Beard, G. P. Landis, S. B. Stebbins

Abstract:	The standard method of using GPS to compare the time of distant clocks is called the common view technique, by which two or more ground stations simultaneously observe a single GPS satellite, or space vehicle (SV). In the most commonly used form of common view, the positions of the SVs must be known, because the time of arrival of an SV signal must be corrected for the travel time, that is, the range to the various stations, divided by the speed of light. However, common view is one form of multilateration in which M stations on the ground simultaneously range to N points in the sky. In general, solutions can always be obtained for the positions of the M groundpoints and N skypoints in a coordinate system anchored to any three of them, if M and N are large enough, and if certain singular geometric configurations of the points are avoided. Common view / multilateration can easily be extended to the GPS case, in which pseudoranges take the place of ordinary ranges, and each SV provides four unknowns to be solved for: the three of position, and one of time. If five stations in known locations measure pseudoranges to four SV points, one may solve for four of the station time offsets relative to a reference station, as well as for corrections to the SV broadcast times and positions. If five stations measure pseudoranges to 13 SV points, one may solve for corrections to the station positions, the SV positions, and all the clocks in the system relative to one clock. We show here how to adapt the principles from the classical geodetic literature on simultaneous ranging to the GPS case, in which clock offsets as well as positions must be estimated. We discuss how to optimize the geographic distribution of common view stations, and the lengths and frequency of times of observation. A proposal for field tests is presented, based on numerical simulations.
Published in:	Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989) September 27 - 29, 1989 The Broadmoor Hotel Colorado Spring, CO
Pages:	463 - 474
Cite this article:	Fliegel, H. F., Beard, R. L., Landis, G. P., Stebbins, S. B., "An Alternative Common View Method for Time Transfer With GPS," Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989), Colorado Spring, CO, September 1989, pp. 463-474.
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