A comparison of GPS common-view time transfer to all-in-view

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 averaging, and under 100 ps at 1 d. Looking at closures including stations in Europe, North America and Japan, we see evidence for a white PM level below 0.5 ns with an averaging time of 1 d, a flicker floor of 100 ps after 3 d, and systematic effects at a level of up to 1 ns. We also show evidence that errors in ionospheric maps and multi-path interference can cause noise processes at least as dispersive as flicker phase noise at 300 ps from 1 d to past 10 d. We conclude that all-in-view GPS time transfer improves stability over common-view for links as long as 5000 km, and is equivalent for links as short as 2500 km. We also find that ionosphere-free time transfer data may provide a significant improvement for averaging past 1 d