GPS載波相位結合動態智慧型適應預測濾波器在頻率同步之應用

Abstract

本論文介紹利用單頻接收機及GPS載波相位觀測量所組成一低成本且高精度的頻率同步系統（GPS 載波相位訓練振盪器）。此頻率同步系統符合具有追溯至國際時頻標準能力（GPS時間）。此外;本系統可以當作第二層時頻標準，應用於頻率同步及精密量測等工作場所或系統之中。如果在無動態智慧型適應預測濾波器作用下，其輸出在一良好頻率參考源比較下，可以當作即時大氣層變動參考，應用在地震預測或氣象學研究上。 為估測一爐控晶體振盪器相對於GPS時間頻率偏差，我們將此爐控晶體振盪器以外頻輸入至一單頻GPS接收機內，藉以取代原來內建單頻接收機振盪器所產生之基頻訊號。因此，爐控晶體振盪器之頻率特性將表現在我們所使用之載波相位觀測量上。然後，對所有可視衛星，利用GPS載波相位在兩個不同觀測時間點，進行時間（一次）差分，如此我們將可估測爐控晶體振盪器相對於GPS時間平均頻率偏差。由於此種單方向直接式單頻接收機之頻率同步系統，主要之影響來自於大氣層之變動延遲。因此，我們提出一新穎動態智慧型適應預測濾波器來降低大氣層影響。修正後平均頻率偏差估測利用一切換式控制器經由數位類比轉換，構成一個大型相鎖迴路系統，控制爐控晶體振盪器輸出。此濾波器之內部參數，是使用一個在理想環境控制下原級鐘，作連續八日單機載波相量觀測，並紀錄個別衛星即時頻率偏差估測，將此估測學習目標送至使用者後，使用者針對每一顆衛星，來進行廣義化訓練調整。 此動態智慧型適應預測濾波器可以用於改善區域性即時大氣層變動延遲影響。在建構時，可以隨著使用者觀測環境作適應性的調整。使用操作上簡單。在大氣層無受重大因素改變之情況下，具有可以每天更新連續使用的強健性。此外；智慧型適應預測濾波器與GPS所廣播的庫爾巴卡電離層群延模式；經由GPS載波相位頻率同步系統比較驗證後顯示；智慧型適應預測濾波器於區域性應用中，其中長期頻率穩定度優於庫爾巴卡即時電離層校正模式。頻率同步系統在動態智慧型適應預測濾波器作用下(GPS載波相位訓練振盪器)；以爐控晶體振盪器10MHz輸出為例；其相對於銫原子鐘10MHz參考頻率，其一天頻率偏差估測值可以從10 等級改善至10 等級，而相對頻率穩定度（修改亞倫方差）也能有從10 等級至10 等級提升。再者; GPS 載波相位訓練振盪器於區域性應用中，其短中期（10s~10000s）頻率穩定度優於商用GPS訓練振盪器。在實際應用上，此智慧型適應預測濾波器使用分散式適應建構過程，對於一般使用者而言，所提供的大氣層變動延遲修正量，改善了頻率同步性能；同時減輕了國家計量研究院(NMI)於設備購置上的成本。龐大計算量也因此建構程序，合理的平均分配給每位使用者。

A low-cost, highly-accurate GPS carrier phase frequency syntonization system (GPS carrier phase-disciplined oscillator, GPSCDO) based on a single-frequency receiver is presented. The scheme can allow traceability to the international time and frequency as disseminated by the GPS. The system can be used in stratum II time/frequency standards, such as site syntonization systems, event measurement, etc. Furthermore, the GPSCDO can monitor atmospheric variations applied to earthquake prediction or meteorology when the dynamic intelligent adaptive forecasting filter is turned off. To estimate the average frequency offsets of an oscillator with respect to the GPS, the oscillator was connected to a time/frequency GPS receiver to replace its original oscillator. Hence, the behavior of the oscillator was determined from the GPS carrier phase observations. The average frequency offsets of the oscillator with respect to the GPS could be estimated by performing difference operations on carrier phase observations of all satellites in view between two measurement epochs. To reduce the interference of the atmospheric delay, a real-time dynamic intelligent adaptive forecasting filter (DIAFF) was proposed. The corrected average frequency offsets were then used by the switch controller to steer the OCXO through a D/A converter. The parameters of the DIAFF were obtained according to the results of an eight-day experiment, in which the GPS carrier phase observations of a stand-alone configuration with a primary clock are recorded for each satellite. The DIAFF can be available to correct locally (smaller than 50 Km) average atmospheric differential delays in real time. The circumstances of the users can be considered in creation of the DIAFF. The DIAFF is available easily and provides day-to-day robustness under regular atmosphere. In addition, the DIAFF is better than the Klobuchar model from the frequency stability analyses of the medium term and long term in the local area. The GPSCDO with the DIAFF can be improved on the estimates of normalized frequency offset of the OCXO with respect to the Cs. clock from the order of 10 to that of 10 and the frequency stability (MDEV) from the order of 10 to that of 10 over 24 hours. Furthermore, the GPSCDO with the DIAFF is better than the commercial GPS disciplined oscillator (GPSDO) from the frequency stability analyses of the short term (10s) and medium term (10000s) in the local area. The decentralized adaptive atmospheric delay correction processes improve frequency syntonization performance of the users, and reduce the cost of the apparatus for the National Metrology Institute (NMI). In addition, a great quantity of computation can be distributed over the users equally.