RESSOX CONTROL OF QZSS DURING COMMUNICATION INTERRUPTION

摘要

The Remote Synchronization System for the Onboard Crystal Oscillator (RESSOX) is a new timekeeping method for the Japanese Quasi-Zenith Satellite System (QZSS), and a remote synchronization system for the onboard crystal oscillator of a satellite and the atomic clock of the ground station. RESSOX is developed with an eye to replacing the onboard atomic clock. One of the serious problems of RESSOX is that the QZSS must have an approximately 35-minute communication interruption twice a day to avoid interfering with the communication of other geostationary satellites when the QZS crosses the equator. During the communication interruption, the onboard crystal oscillator will be controlled, not by RESSOX, but by an onboard local system. Two control algorithms were proposed: (1) the averaging of adjacent voltage data and (2) the first-order extrapolation of adjacent voltage data prior to communication interruption. As the behavior of the crystal oscillator is statistical, we attempted to apply a statistical method using our RESSOX hardware/software simulators for the evaluation. At least 12 experiments/simulations were conducted for each case. The standard deviations of the maximum synchronization errors during the 35-minute communication interruption between the onboard crystal oscillator of the satellite and the atomic clock of the ground station were compared. The results of simulations and experiments correspond to each other. In general, the results obtained by averaging show better synchronization than those obtained by first-order extrapolation. The best result was given by the case of averaging 100 adjacent voltage data, and the standard deviation of the maximum synchronization error was 2.80 ns.