Recent Improvements in GPS Carrier Phase Frequency Transfer

Jérôme Delporte, Flavien Mercier

Abstract:	GPS carrier phase frequency transfer is a convenient method to compare distant ground clocks. It requires multi-channel dual-frequency GPS receivers in both ground stations. In this paper, CNES specific software for GPS carrier phase frequency transfer is used. It overcomes the usual limitation of some GPS solutions: the day boundaries discontinuities. These discontinuities in the clock solution occur if the data are analyzed in daily independent batches. It is also possible to down sample the measurement files. These two functionalities allow us to perform a continuous GPS carrier phase frequency transfer on long durations. Results on different baselines are presented and discussed. For instance, on medium baselines, stabilities reaching 1.10-15 (Allan deviation) on one day are commonly obtained. On transatlantic baselines, stabilities are degraded due to the low number of satellites in common view. In the Time/Frequency laboratory of CNES, several GPS receivers and frequency standards are available. With this technique, we can estimate CNES H-Maser frequency stability (from 3.104 s on, at the level of 4.10-15). Moreover, we can compare the obtained results with local comparisons, including versus a cryogenic sapphire oscillator. Besides, the precise orbit restitution software developed at CNES (ZOOM) is able to solve the clocks of a GPS network (ground and on-board clocks) on several days. The formulation is slightly different from the previously mentioned software and the models are also different (for example the phase windup can be modeled). We compare and discuss some frequency transfer results obtained with both approaches. On medium baselines, very similar results are obtained. But on transatlantic baselines, better results are achieved provided that a good network geometry is chosen.
Published in:	Proceedings of the 37th Annual Precise Time and Time Interval Systems and Applications Meeting August 29 - 31, 2005 Vancouver, Canada
Pages:	699 - 706
Cite this article:	Delporte, Jérôme, Mercier, Flavien, "Recent Improvements in GPS Carrier Phase Frequency Transfer," Proceedings of the 37th Annual Precise Time and Time Interval Systems and Applications Meeting, Vancouver, Canada, August 2005, pp. 699-706.
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