The Time Parameter Of Satellite Navigation And Its Test Method

The current satellite navigation system is based on time measurement, and the accurate and stable time is the most basic guarantee of satellite navigation system operation. As the expression of time information in satellite navigation system, the time parameter is not only the prerequisite of achieving position, velocity and other functions, but more directly relates to the system service performance, so it is necessary for the time parameter of satellite navigation system to be comprehensively analysed and tested.Based on comprehensive analysis of the satellite navigation positioning and timing technology, the paper systematically concludes the functions and characteristics of time parameters in satellite navigation system, which studies the characterization methods of time parameters in navigation message and user end as well as the impact on system service performance. According to the users characteristics, the concept and method of the bias betweem UTC time broadcasted by the satellites and actual UTC is proposed, while the paper studies the test methods of time parameters to synthetically test and evaluate the timing performance of whole navigation system. Through analysis and test of the main time parameters in GPS,GLONASS, Bei Dou navigation system, the test methods proposed in this paper are verified.The main research work and innovation points in the paper are reflected in the following aspects:(1)From the user perspective, the changes characteristics of time parameters during positioning and timing process are studied, and the paper summarizes the contents of time parameters in navigation message and user end, which synthetically gives the variation and characteristic of time parameters, with its analysis of the test points.(2) The paper studies the test methods of traceability model in navigation message, which tests and analyses the traceability models of GPS, GLONASS and Bei Dou through designing correlation experiment. The results show the prediction error of GPS traceability model within ±3ns is better than GLONASS and Bei Dou,but Bei Ddou traceability model exists a bigger prediction error in the range of-50ns~100ns. Using the experiment platform the characteristic of navigation systemtime obtained by users is analysed, we find both GPST and BDT show a monotonous trend of fluctuation in two months testing, with GPST smaller fluctuation while BDT gradually approaching to UTC stably. GLONASST appears to a larger phase adjustment in January 2015, and later the stability is less than BDT.(3)According to the difficulty in testing the satellite clock model, the paper proposes a test method of system time broadcasted by the satellites. From the user perspective, we evaluate the system time performance obtained by each satellite signal instead of the error of satellite clock model, and this conversion clears the test object not only making the testing process easy operation but also reflecting the users’ actual errors in positioning and timing. The results show the errors of system time broadcasted by GPS satellites are better than GLONASS and Bei Dou. Finally we design a method of differential satellite clock model correction to verify the test results. Comparing with the impact on position by using the satellite clock model in navigation message, adding the paper’s correction result the position errors are significantly reduced, and the improvement rate of GPS, GLONASS and Bei Dou position errors are partly 79.91%, 75.15% and 50.85%, which verifies the correctness of the test method.(4)As a difficulty in navigation area the receiver delay is focused as the study object in the paper, and the paper proposes a calibration method of the receivers based on clock steering to calibrate the two receivers used. The frequency bias in the GPS/GLONASS receiver increases to a linearly trend in the range of 0~13ns, with the calibration uncertainty of GPS L1 1.8ns, L2 1.6ns, GLONASS L1 5.2ns. However,the Bei Dou receiver delay represents a strong correlation with the phase offset of the external input 1PPS and 10 MHz signals, and the delay exists differences between the receiver under continuous operation and on-off operation which can be easily ignored.Through designing the zero-baseline comparison experiment to verify the calibration result, calibration uncertainty of Bei Dou B1 and B2 is 2.8ns that of B3 is 2.3ns.(5)From the system perspective, the paper studies the timing test methods of single satellite and multiple satellites, which proposes the characterization system of the bias between UTC broadcasted by the satellites and actual UTC, and referring to the timing performance of three navigation system we develop a comprehensive test and evaluation experiment. The results show the bias between the time broadcasted by GPS satellites and UTC is about-30ns~20ns, with the timing error better than-15 ns.GLONASS system time appears to a jump transition in August 2014 with timing errorlarger than-200 ns before and gradually less than-20 ns after, and comparing with the same period circular T data we find GLONASST-UTC reported by circular T exists around 220 ns difference. However, the bias between the time broadcasted by Bei Dou satellites and UTC represents the larger fluctuation, which leads to a large timing error in the current Bei Dou system because of Bei Dou traceability model error, thus users obtain the UTC time from Bei Dou satellite signal existing large bias against the actual UTC.According to the test methods and results of the bias betweem UTC time broadcasted by the satellites and actual UTC in the paper, we can further understand the positioning and timing performance of satellite navigation system as well as analysis of the improvement direction, which provides support for the construction and application of Chinese satellite navigation system. Meanwhile, in order to lay the foundation for further optimizing the system design and improving the timing performance the paper has been publishing the part of evaluation results through internet in the form of periodic FTP, which lets the users conveniently select to use.