A Long-Term Comparison of GPS Carrier-phase Frequency Transfer and Two-Way Satellite Time/Frequency Transfer

Christine Hackman, Judah Levine, Thomas E. Parker

Abstract:	GPS carrier-phase frequency transfer (GPSCPFT) and two-way satellite time and frequency transfer (TWSTFT) were performed along three transatlantic links over the 6-month period 29 January – 31 July 2006. The GPSCPFT and TWSTFT results were subtracted in order to estimate the combined uncertainty of the methods. The frequency values obtained from GPSCPFT and TWSTFT agreed at 1.8 to 3.8·10-16 RMS for averaging times of 30 d, with no single value of yGPSCPFT – yTWSTFT exceeding 5.5·10-16. These RMS frequency-accuracy values were equal to or less than the frequency-stability values sy(GPSCPFT) – y(TWSTFT) (t) (or TheoBR (t)) computed for the corresponding averaging times; in general, no frequency bias between GPSCPFT and TWSTFT was observed. The transfer noise of the links varied with time of year, which was especially noticeable in the yGPSCPFT – yTWSTFT values obtained for 10-15 d averaging times: yGPSCPFT – yTWSTFT (10 d) sometimes became as large as 2·10-15. It is not yet clear what caused these variations. RMS (yGPSCPFT – yTWSTFT, 10 d) ranged from 0.7 to 1.1·10-15, with these RMS values approximately equal to sy(GPSCPFT) – y(TWSTFT) (t = 10 d, 21 h). Day-boundary discontinuities were not removed or otherwise circumvented in this experiment; we hope to reduce the uncertainty at shorter averaging times (e.g., 10 d) through better management of these discontinuities, along with improved understanding of the seasonal components.
Published in:	Proceedings of the 38th Annual Precise Time and Time Interval Systems and Applications Meeting December 7 - 9, 2006 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	485 - 498
Cite this article:	Hackman, Christine, Levine, Judah, Parker, Thomas E., "A Long-Term Comparison of GPS Carrier-phase Frequency Transfer and Two-Way Satellite Time/Frequency Transfer," Proceedings of the 38th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 2006, pp. 485-498.
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