High-accuracy time transfer via geostationary satellites: preliminary results

Signal-delay phase measurements have been performed with Ku-band Earth station and VSAT (very-small-aperture terminal) facilities in various loop-around schemes using both a satellite simulator and geostationary satellites. Stability plots show that the standard deviation of pair differences (σ_y) is 4×10^-10 _τ^-1 for a C/No (carrier-to-noise density) ratio of 65 dB-Hz. This white-noise behavior continues for several days, when satellite simulator data shows σ _y to be 3×10^-15. Absolute phase-delay measurements show reproducibility to better than 1 ns over a 16-day sample time. This suggests the potential for accuracy to this level, given an appropriate calibration. A measurement method is described which determines the principal time-delay constant affecting the accuracy of time synchronization using a two-way satellite communications technique