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  • Anomalies Influence Analysis of the Remote Synchronization System RESSOX for the Japanese Quasi-Zenith Satellite System

    Paper number



    Mr. Fabrizio Tappero, University of New South Wales, Australia



    The Japanese Quasi-Zenith Satellite (QZS) system is a three satellite multi-service system conceived to improve positioning performances, satellite availability and position accuracy of the presently available global positioning system (GPS), mainly in urban areas where high buildings could easily reduce the number of visible GPS satellites.
    GPS satellites generate their positioning signal by means of  independent on-board atomic clocks. However, unlike classic worldwide GPS systems, the orbit design of the Japanese QZS system is such that if an appropriate observation point is chosen, each satellite can actually be visible for its whole orbital period. This means that QZS on-board clocks could theoretically be remotely synchronized to a main atomic clock located in the master ground station. In fact, if a remote time synchronization system would be adopted, satellites will not need independent clocks anymore, instead they would simply act as remotely controlled clocks. Bulky and expensive on-board atomic clocks would become unnecessary.
    A possible scheme concept for the remote synchronization system for the on-board crystal oscillator (RESSOX) is now under study. By means of a feedback/feed-forward loop, RESSOX keeps a lock-step the ground station time reference with the voltage controlled crystal oscillator (VCXO)  on board each QZS; The time reference employed in the ground station is a cesium or hydrogen maser atomic reference, and the time reference employed on board the QZS is an ultra stable VCXO.
    The synchronization accuracy of the RESSOX network directly influences the performances of the whole QZS augmentation system. A given anomaly in the synchronization network will immediately compromise the positioning performances of the combined system QZS/GPS. Moreover, there are unavoidable events that could stress the behavior of the synchronization network. For instance, every time the QZ satellite cross the equatorial region, communications with the ground station must me shut down for approximately 20 minutes. During these periods the RESSOX synchronization network cannot be utilized, and satellite clocks will have to act on their own.
    The paper hereby presents an analysis of the positioning performance when anomalies in the remote synchronization scheme occur. A software simulator of the satellite segment, ground segment and synchronization/correction communication channel is employed to study the behavior of the RESSOX scheme during inevitable communication interruptions and other unexpected anomalies. Effect on the positioning accuracy is extensively analyzed. Different scenarios are theorized and the influence on the positioning quality of on-board clocks of different qualities is analyzed. QZS on-board time reference and ground atomic clock de-synchronization failure are theorize and their effects on the positioning are analyzed.
    Abstract document


    Manuscript document

    IAC-06-B3.5.07.pdf (🔒 authorized access only).

    To get the manuscript, please contact IAF Secretariat.