利用GPS估測振盪器之頻率穩定度

一直以來，在高速電信網路、定位導航、電力系統、儀器測量等領域中，高精準度的頻率振盪器都扮演非常重要的角色。因此如何使振盪器達成高精準度的同步，就成了各個時頻領域應用技術所要面對的挑戰之一。而全球定位系統（Global Positioning System，GPS）除了可以提供廉價且精密的導航之外，其高精度的時頻訊號，可以幫忙我們解決頻率同步上的許多問題。因此，藉助於GPS找出振盪器的頻率偏差，就是本篇論文所要探討與解決的問題。然而，衛星廣播訊號到各個接收器的過程中，有許多因素會造成訊號的誤差產生。而這些誤差來源中，我們有興趣的是電離層延遲效應與時鐘誤差。時鐘誤差即為我們最在意的振盪器頻率偏差。為了找出時鐘誤差，我們必須要想辦法估算電離層延遲效應，然後將其扣除。在本篇論文中，我們採用兩種方法來解決電離層延遲。第一種為利用電離層延遲數學模型，先找出TEC值，然後藉以預測電離層延遲效應之影響，將量測到的誤差量減去預測的結果，便可得到時鐘誤差量。第二種，則是利用變異數回歸建模理論以及方法，先計算出模型之參數，再由參數來預測電離層延遲效應，將量測之時間誤差量減去預測之結果，即可得到時鐘誤差量。採用電離層模型的優勢在於，可以預測單顆衛星對接收器所發生的電離層延遲效應，因此接收器可以得到關於定位導航的資訊，但是估測時鐘誤差的效果卻稍遜於變異數回歸建模；而採用變異數回歸建模，則可以擁有較佳的預測效果，但是卻喪失了定位導航的資訊。而本篇論文的主題，採用變異數回歸建模似乎是更為恰當的方法。

關鍵字

電離層延遲效應；時鐘誤差；頻率穩定度

並列摘要

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.

並列關鍵字

ionospheric delay effect ； clock error ； frequency stability

參考文獻

[2] Francois Vernotte, Jacques Groslambert, and Jean Jacques Gagnepain, “A New Method of Measurement of the Different Types of Noise Altering the Output Signal of Oscillator.”, IEEE Transaction on Instrumentation and Measurement. Vol. 42, No. 6, December 1993.

[4] Jacques Rutman and F.L. Walls,“Characterization of Frequency Stability In Precision Frequency Sources.”.

[7] Steven M. Kay and Stanley Lawrence Marple, JR., ‘’Spectrum Analysis – A Modern Perspective. ”Proceedings of the IEEE, vol. 69, No. 11, November 1981 pp.1380 – 1419.

[1] Elliott D. Kaplan, “Understanding GPS: Principles and Applications”, Artech House Publishers, Boston, 1996.

Google Scholar

[3] Guochang Xu, “ GPS – Theory, Algorithm and Application”, Springer

Google Scholar

國際替代計量

利用GPS估測振盪器之頻率穩定度

全文下載

主題瀏覽