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In almost all the studies, the differential receiver calibration and the link calibration had been discussed separately as if the two calibrations were completely independent. In fact, in the sense of the total delay for UTC time transfer, the difference between the receiver and link calibrations is not how to perform the calibration measurement but how to use the measurement data. The two calibration...
Accurate GNSS (Global Navigation Satellite System) time transfer needs accurate satellite orbit information. Since Nov. 2009, the GLONASS time transfer is introduced in UTC generation. The precise and timely GLONASS orbit information is indispensable for Circular T computation. In this paper, we compare the GLONASS orbits produced by different analysis centers. We study the differences of the products,...
The CCTF CGGTTS data formats are used worldwide in the applications of various societies from the UTC/TAI production and scientific studies to all levels of commercial usages. Its design was based on the GPS receiver technique in the 1980s. With the progress of the new GNSS receivers and new T/F transfer techniques, its short points are becoming evident, e.g. the convention that for a tracking arc...
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...
We discuss the introduction of a new time transfer technique for computing time links for TAI. Precise point positioning uses GPS dual frequency carrier phase and code measurements to compute the link between a local clock and a reference time scale with the precision of the carrier phase and the accuracy of the code. The time link between any two stations can then be computed by simple difference...
Carrier phase GPS observations between a geodetic receiver at the Physikalisch-Technische Bundesanstalt (PTB) and two geodetic receivers at the USNO are processed using applications and extensions of the GIPSY and Bernese GPS software packages. Their results are compared with two way satellite time and frequency transfer (TWSTFT) data. It is found that algorithms that eliminate day-boundary effects...
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...
The network of time links for the computation of TAI has always be chosen such as to allow a unique solution, i.e. not using any redundancy. In the present situation, many links can be computed with two or more techniques (mostly Two Way time transfer -TW- and Global Positioning System -GPS-) and the TW network itself is highly redundant. Therefore it makes sense to use all the available information...
Unlike GPS, the GLONASS P-code is broadly accessible. This paper discuss GLONASS capabilities and prospects in terms of precise time transfer. We have tested GLONASS common-view time transfer using the C/A- and P-code, over time links varying in length from about 800 km to 9200 km. The raw GPS and GLONASS data were collected using 3S navigation receivers, and were corrected using IGS precise orbit...
The network of time links for the computation of TAI has always be chosen such as to allow a unique solution, i.e. not using any redundancy. In the present situation, many links can be computed with two or more techniques (mostly TW and GPS) and the TW network itself is highly redundant. In addition, the covariance matrix for the measurements from these two may now be determined with adequate uncertainty,...
All-in-view time transfer is being considered to replace common-view for computing the links of International Atomic Time (TAI). The components in all-in-view GPS time transfer that do not cancel as they do in the common-view technique are the satellite clock estimate and the ephemeris estimate. We show that these components average down as white phase noise with a typical level of 2 ns with 13 minute...
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