GPS Carrier Phase Frequency Syntonization with the Dynamic Intelligent Adaptive Forecasting Filter

• Main Authors: Chia-Lung Cheng, 程家龍
• Other Authors: 張帆人
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/77241063984199584231

博士 === 國立臺灣大學 === 電機工程學研究所 === 94 === 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.