Estimate Frequency Stability of Oscillators by Using GPS
Date Issued
2004
Date
2004
Author(s)
Li, Cha-Bin
DOI
zh-TW
Abstract
Precise frequency oscillators play very important roles in many applications, for example: high-speed communications, navigations, instrumentation etc. How to obtain more precise clock become the challenges of time and frequency applications technology. The GPS(Global Positioning System) not only can provide low cost and precise navigation information, but also can solve the problem of frequency synchronization.
To obtain the frequency offset of an oscillator via GPS is the topic to of this thesis. However, there are errors which pollute the satellite broadcast signals.
Among these error sources, what we most concern are ionospheric delay effect and clock error. Clock error is caused by frequency offset of oscillator. In order to find out clock error, ionospheric delay effect will be estimated and then be subtracted.
We propose two methods to solve the problem of ionospheric delay. The first one uses the mathematic model of ionospheric delay effect. Then the forecast ionospheric delay can be calculated when the TEC value is estimated. We can get clock error by subtract the forecasted ionospheric delay. The second method uses ARMA model of approximate the ionospheric delay. We estimated the parameters of the ARMA model first, and forecast the ionospheric delay effect by ARMA model. We subtract the forecasted ionospheric delay from measured errors, and then we find the clock error.
The advantage of using the mathematic model of ionospheric delay effect is that one won’t lose the navigation information. However, the ARMA model method is unable to get the navigation information, but have the more precise estimation of clock errors than the first method. ARMA model seems to be more appropriated for this thesis.
Subjects
電離層延遲效應
時鐘誤差
頻率穩定度
ionospheric delay effect
clock error
frequency stability
Type
thesis
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