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Study and Application of Time Scale in Satellite Navigation System

Author: WuZuoWei
Tutor: YongShaoWei
School: National University of Defense Science and Technology
Course: Information and Communication Engineering
Keywords: Satellite Navigation Time Synchronization Time Scale Algorithm Timekeeping System Time Reference ALGOS Algorithm AT1 Algorithm Kalman Algorithm Wavelet Decomposition Algorithm Atomic Clock Noise Power Law Model Allan Variance Atomic Clock Noise Identification Atomic Clock State Estimation Time Sever
CLC: TN967.1
Type: Master's thesis
Year: 2011
Downloads: 130
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Abstract

The satellite navigation system is actually a time synchronization system. The time reference of the system is the key factor that affects the accurancy of positioning and time keeping of the whole system. At present, the time system of the Beidou II satellite navigation system is under construction. This is the background of this paper. The study of the key technologies of the time system of the satellite navigation system in this paper mainly concentrates on the establishment and maintenance of a time reference and the establishment of a timekeeping system.The time scale algorithm is the key of the establishment of a time reference. The theoretical basis of the time scale algorithm is the atomic clock noise model. This paper described the basics of atomic clock noise model, including the atomic clock output signal model, the atomic clock noise model, the frequency stability of atomic clocks and its description, the methods to identify atomic clock noise. This paper described the major time scale algorithms, including ALGOS algorithms, AT1 algorithm, Kalman algorithm, the wavelet decomposition algorithm, and discussed their ideas and basic principles, and described the theoretical limit of improving frequency stability by using the weighted algorithm. Conclusions could be got through comparative analysis that Kalman algorithm is more suitable for satellite navigation systems. Therefore, it is recommended that the establishment of the time reference of the Beidou II satellite navigation system use Kalman algorithm.This paper realized the analysis of the performance of the atomic clocks calculating the time scale. The frequency stability and noise characteristics of atomic clocks were analysed by their Allan variance and their dynamic model. The noise coefficient and noise variance of these clocks were obtained by Allan variance inversion methods, which further the study of the atomic clocks’performances. The results of these two different Allan variance inversion mothods were compared and analyzed. This paper realized ALGOS algorithm, analyzed the simulation results of the time scale got by equal-weighted algorithm and weighted algorithm and their disadvantages. Since the weight is usually correlate to one kind of noise, and the short-term stability and long-term stability of the time scale could not achieve optimal at the same time, it is necessary to study the Kalman algorithm which can eliminate several kind of noise.This paper studied the Kalman filter in the use of satellite navigation systems in depth, including that in the use of estimating the state of the atomic clocks state and in the use of the establishment of a time scale. This paper realized these two use, and conclusions could got by analyzing the time deviation, frequency deviation, frequency drift, Allan deviation and the noise coefficient. All these conclusions have proved that Kalman algorithm can achieve better results in these two ways. Compairing with ALGOS algorithm, the results of Kalman algorithm were obviously better than ALGOS algorithm which could only eliminate one main kind of noise. The long-term stability improved more significant when using Kalman algorithm. Therefore, Kalman algorithm applied to state estimation of atomic clocks and establishment of a time reference of the satellite navigation system is of obvious advantage.This article described generation and distribution of the time frequency signal, known as the establishment of a timekeeping system. Time server plays an important role in time synchronization. In this paper, since many laboratories do not use a time server due to the reasons such as high cost, a PC-based network time server was designed. Tests indicated that the performance of the network time server satisfied the general engineering requirements. It is simple-configured, easy and flexible, with low cost, and has a high practical value.At last, the thread, creative points and research work of this dissertation were summarized and reviewed. And the next research to be carried out was also presented. The researches will have impact on the constructing Beidou II satellite navigation system.

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