Optimal Time Transfer

James R. Wright and James Woodburn

Abstract:	We have designed an optimal time transfer algorithm using GPS carrier-phase and pseudorange measurements. This will enable the near-real-time estimation of the difference between the phase of a stable real-time UTC ground clock attached to a GPS ground receiver and the phase of each NAVSTAR spacecraft clock in the ensemble of GPS spacecraft. We propose a master filter (MF) to drive multiple instances of spawned filters (SF) and fixed-epoch smoothers (FES). The MF is designed to map all GPS carrier-phase measurement information of eachGPS ground-station/NAVSTAR pass into the complete MF state estimate of all NAVSTAR parameters and all station parameters, with all serial correlations and all cross-correlations accounted for. Each SF runs forward with time while the FES linearly maps measurement information backwards to fixed epochs for individual NAVSTAR spacecraft. FES estimates are then folded into the MF as pseudo-measurements. The resulting time-transfer algorithm is an autonomous forward-running sequential estimator, with no state-sized matrix inverse calculations required.
Published in:	Proceedings of the 41st Annual Precise Time and Time Interval Systems and Applications Meeting November 16 - 19, 2009 Hyatt Regency Tamaya Resort Santa Ana Pueblo, New Mexico
Pages:	359 - 370
Cite this article:	Wright, James R., Woodburn, James, "Optimal Time Transfer," Proceedings of the 41st Annual Precise Time and Time Interval Systems and Applications Meeting, Santa Ana Pueblo, New Mexico, November 2009, pp. 359-370.
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