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Two-Way Satellite Time and Frequency Transfer (TWSTFT or TW) is one of the primary time transfer techniques for UTC generation. In this framework the Triangle Closure Calibration (TCC) method has been used to calibrate links between certain laboratories whose links to the pivot lab are directly calibrated. TCC is based upon requiring the closure of three co-joined links to be zero. In this paper,...
In the frame of the BIPM pilot project [8] on the accurate calibration aiming at unifying the UTC time link calibration uncertainties ≤ 2 ns, we studied the instability of the BIPM travelling calibrator (StdB). Using the time stability (Tdev), the closure measurements and the inter-comparison of the two independent receiver systems in the StdB, we analyzed one year data to investigate the short- and...
Precise time transfer is one of the essential works for time-keeping laboratories in maintaining the standards of time and frequency. At the National Metrology Centre (NMC) in Singapore, we have been seeking to improve the time scale performance and time transfer capability by employing different time transfer techniques. Currently, three different time transfer systems are used in the laboratory,...
The major techniques used for the international UTC/TAI time and frequency transfers are the two independent space techniques: TWSTFT (two-way satellite time and frequency transfer) and GNSS (global navigation satellite system: GPS, GALILEO, GLONASS etc.). Comprised of multi- techniques, this system is highly redundant, of which not a single technique has dominant advantage with respect to the others...
NTSC (National Time Service Center) is responsible for Chinese national time scale generation and has being applied TWSTFT (two-way satellite time and frequency transfer, TW for short) for time transfer since 1998. NTSC was one of the first UTC laboratories practicing TWSTFT in China. From 2002 to 2004, TWSTFT was the major technique for NTSC contributing to UTC. Since 2007, direct NTSC-European TWSTFT...
TWSTF (TW) is a precise time transfer technique and has being used to generate the TAI since 1999. From the beginning with only 3 measured points per week over a few baselines to now 12–24 points per day and measured as a worldwide network, the TW observable becomes highly redundant. However single baseline is still the only geometry in TAI time transfer practice. As shown in Fig. I-1, among the 35...
The time transfer techniques used to generate TAI are currently the TWSTFT (TW), GPS C/A, and GPS P3. About 19% of all TAI laboratories possess P3, 12% possess TW backed up with P3, i.e., in total only 31% of the TAI laboratories transfer 100% of the primary frequency standards (PFS) including all the Cs fountains and 80% of the total weighted clocks for TAI. GPS carrier phase (CP) data are co-products...
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