Asymmetry Effects of Satellite motion on Two-Way Time and Frequency Transfer

This study analyzes the asymmetry effects of propagation delay measurements caused by the relative velocity between a satellite and ground stations. We provide the derivation of the basic equations for those asymmetry effects. In advanced TWSTFT techniques, such as dual pseudo-random noise ( DPN) codes and TWSTFT carrier phase, the phase is continuously tracked and accumulated in measurements. Thus, the second-order terms for accumulated Doppler shift are also discussed. Ideally, the results of TWSTFT should reflect only the asymmetry on bi-direction propagation delays. Then, we compute the correction for two-way delay asymmetry, accumulated Doppler shift difference, and Sagnac effect through the derived equations. The calculated results are compared with the experimental TWSTFT data. The time deviations at the 12-hour averaging time are reduced from 66 ps to 60 ps after applying the correction to the raw DPN TWSTFT data in NICT-TL link.