Speaker
Description
As part of International Atomic Time (TAI -- Temps Atomique International) definition, national observatories regularly share their atomic (hydrogen, cesium ...) clock signals through geostationary satellite links. The Two Way Satellite Time and Frequency Transfer (TWSTFT) system has been developed to cancel the impact of the microwave link and synchronize clocks distributed continents away with sub-ns accuracy (light travels 30 cm during 1 ns).
These signals are broadcast over the ether and accessible to any knowledgeable user who might want to synchronize their clock.
Geostationary satellites, usually considered at a fixed location above the equator, are however subject to gravitational forces and must remain within a window size of 0.1 degree, or a sphere of 30-km radius (light travels 30 km in 100 us). The challenge in compensating for the impact of varying position of the geostationary satellite for accurate synchronization of clocks in a passive reception scheme lies in identifying the satellite location and compensating for its variation.
While Global Navigation Satellite Systems (GNSS) including the Global Positioning System (GPS) rely on spaceborne atomic clocks for accurate time transfer to the receiver allowing by trilateration for positioning and timing (Position, Velocity and Time -- PVT -- solution), we will show in this presentation that
- the TWSTFT signal are readily received with a consumer-grade satellite-TV reception parabolic reflector antenna fitted with a Software Defined Radio (SDR) receiver able to collect signals around 1.2 GHz on a 5-MHz bandwidth
- correlation and super-resolution using parabolic fit of the correlation peak allows for sub-ns timing resolution despite the 4-MHz bandwidth signal
- the spatial diversity of the emitting references, assumed to be synchronized, allows for recovering the attitude of the satellite,
- that publicly available ranging measurements from these reference sources match the observations.
Hence, accurate timing of passive receivers of TWSTFT requires solving issues reminiscent of GPS ... upside down.
| Talk Length | 30 Minutes |
|---|---|
| Acknowledge | Acknowledge In-Person |
