3,070 research outputs found
Remote atomic clock synchronization via satellites and optical fibers
In the global network of institutions engaged with the realization of
International Atomic Time (TAI), atomic clocks and time scales are compared by
means of the Global Positioning System (GPS) and by employing telecommunication
satellites for two-way satellite time and frequency transfer (TWSTFT). The
frequencies of the state-of-the-art primary caesium fountain clocks can be
compared at the level of 10e-15 (relative, 1 day averaging) and time scales can
be synchronized with an uncertainty of one nanosecond. Future improvements of
worldwide clock comparisons will require also an improvement of the local
signal distribution systems. For example, the future ACES (atomic clock
ensemble in space) mission shall demonstrate remote time scale comparisons at
the uncertainty level of 100 ps. To ensure that the ACES ground instrument will
be synchronized to the local time scale at PTB without a significant
uncertainty contribution, we have developed a means for calibrated clock
comparisons through optical fibers. An uncertainty below 50 ps over a distance
of 2 km has been demonstrated on the campus of PTB. This technology is thus in
general a promising candidate for synchronization of enhanced time transfer
equipment with the local realizations of UTC . Based on these experiments we
estimate the uncertainty level for calibrated time transfer through optical
fibers over longer distances. These findings are compared with the current
status and developments of satellite based time transfer systems, with a focus
on the calibration techniques for operational systems
Demonstrator of Time Services based on European GNSS signals: the H2020 DEMETRA Project
During 2015-2016, a European Consortium of 15 partners from 8 different
countries, developed the DEMETRA (DEMonstrator of EGNSS services based
on Time Reference Architecture), a project funded by the European Union
in the frame of the Horizon 2020 program. This project aims at
developing and experimenting time dissemination services dedicated to
specific users like traffic control, energy distribution, finance,
telecommunication, and scientific institutions. Nine services have been
developed. These services provide time dissemination with accuracy
levels from millisecond to the sub-ns, and also additional services like
certification, calibration, or integrity. Five of these services are
based on the European GNSS.
After a development phase (see PTTI 2016 presentation) the full DEMETRA
system has been working during six months for demonstration. The paper
will report about the experimentation results, showing performances and
limits of the proposed time dissemination services, aiming to foster the
exploitation of the European GNSS for timing applications
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