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We have developed a new control method for the QuasiZenith Satellite (QZS) remote synchronization system for an onboard crystal oscillator (RESSOX). The new method utilizes both L1 and L2 positioning signals of the QZS. We also found that precise orbit information and the estimation of delays, such as those caused by the ionosphere and troposphere, are not necessary to realize the RESSOX technology. The estimation of the delays of the L1-, L2- and Ku-band signals caused by the ionosphere and other sources can be calculated separately during feedback control, and the results of Ku-band delay are used to generate the RESSOX control signal. The simulation results showed that synchronization of within 3 ns between the ground site clock and the QZS site clock is achievable. Experimental results on the ground also confirmed that synchronization within 3 ns is feasible.

A remote synchronization system for the on-board crystal oscillator (RESSOX) of the QZSS is proposed. Aimed at offering an alternative architecture for the classic GPS time-keeping system (TKS), the proposed system consists of a synchronization framework where an ultrastable atomic clock, localized at the ground station, is kept synchronized to a second time reference, a voltage-controlled crystal oscillator (VCXO), on-board the QZSS satellite. Based on orbit calculations and delay predictions, feedback and feed-forward control guarantee the correct synchronization of the on-board time reference and the ground-station atomic clock. Compared with the classic GPS TKS, the RESSOX scheme offers several advantages in terms of accuracy, cost, weight, and power consumption. An extensive explanation of this novel design is presented. Differences and advantages of the proposed system are compared with the classic atomic clock scheme.

The quasi-zenith satellite (QZS) system (QZSS) is a Japanese project that was started in 2003 with the aim of positioning services. A simulation and experiment on a new timekeeping method for the QZSS was conducted on the ground. The remote synchronization system for the onboard crystal oscillator (RESSOX) of the QZS functions by maintaining an uplink to receive time information from a ground station (GS) equipped with accurate atomic clocks. The required apparatuses for the RESSOX are described. Some simulation and experimental results obtained on the ground, which indicate the feasibility of synchronization to within 10 ns between the GS and the QZS, are demonstrated and compared.