Software Design Of System Time Traceability

As a test system of navigation and satellite time service the navigation systemundertakes the system experimental tasks, and its performance is the decisiveinfluence on the function of that system. The system time of this navigation system isa paper time, and is calculated only by the ground atomic clocks through compositingclock algorithm; its physical realization is the time and frequency signal outputted bythe ground master clock of system. The navigation system has two functions whichare navigation and time service, According to the recommendation of ITU, thedifference between the navigation system time and UTC should be kept within100ns.That means that the system time and UTC must be synchronized; that is to say,the system time is traced to UTC. In view of the characteristics of the navigationsystem, there is not direct time link between the system time and UTC, its systemtime must be steered to national standard time UTC(NTSC) to ensure that the timedifference of UTC and the system time is less than100ns. At present, methods of longdistance precise time comparing include the GNSS common-view and TWSTFT etc.In this thesis the GNSS satellite common-view technique is used in the long distancetime comparing. Through automatic data transmission, data processing, and real-timedynamic traceability model, the deviation between the system time and the referencetime UTC(NTSC) is obtained, and then the time prediction model is established. Theparameters of the trace model are transmitted to the frequency control unit, then thenavigation system time can be steered to the UTC(NTSC) accurately. The maincontent of the study include:(1) In this thesis the current situation at China and abroad of satellite navigationare discussed, and the GNSS common-view and two-way satellite time transfers areanalyzed.(2) The characteristic of this navigation system time traceability test system areanalyzed particularly, based on the construction of navigation system, the timetransfer techniques of the system traceability are further studied. The error and delaycorrection in the process and the data preprocessing algorithm are analyzed. The timedifference forecasting techniques based on the quadratic polynomial model，greymodel and combining model of fixed sliding window dynamic forecasting methodsare studied. The long-term and short-term forecast accuracy of the different forecastwindow size is researched. Finally the appropriate forecast algorithm and the window size are determined.(3) The system time traceability software is developed based on Visual C++6.0.The software of the each module and function are introduced. The software in thesimulation of the real environment to achieve the navigation system time is steered toUTC(NTSC) accurately, and realize the data communication with other units.(4) Finally, the result of calculation by software is analyzed, and the overalldesign is validated. The modular of software are designed whether or not to satisfy theexpect design goal and the results of performance are tested.