Development of the TWSTFT carrier-phase technique at LNE-SYRTE
Abstract
The Two-Way Satellite Time and Frequency Transfer (TWSTFT) method (Achkar at al. 2006) permits to compare two remote atomic clocks by using a microwave link through a geostationary satellite. The best performance reachable today at OP is achieved on the Ku band link with a frequency stability of 8×10^-16 at one day (Zhang et al. 2009). In order to improve stability of the two-way links in the short term, the TWSTFT carrier-phase is the most appropriate method. The work proposed here is limited to the development of the TWSTFT carrier-phase method. The main idea is to calculate the offset between the frequencies of the two clocks located each one in a different station. The Doppler's effect is taken into consideration regarding the spread of the signal between each station and the satellite and vice versa. Note that, one Doppler coefficient corresponds to each Station-Satellite link in both directions. The same hardware is used in the two methods. We establish the equation system of the TWSTFT carrier-phase technique composed by four nonlinear equations with four unknown values which are : the first Doppler coefficients, the satellite's local oscillator frequency and the frequency offset of the distant clocks. This system cannot be solved directly (Fonville et al. 2004). As a first approach, we use the Newton-Raphson method to transform the nonlinear system to a linear one. Then, the singular value decomposition technique is used to solve the resulting linear system.
- Publication:
-
Journées Systèmes de Référence Spatio-temporels 2010
- Pub Date:
- October 2011
- Bibcode:
- 2011jsrs.conf..280K