Research On Time Comparison Based On GPS Precise Point Positioning And Atomic Clock Prediction

GPS precise point positioning (PPP) which can be implemented only by one dual-frequency receiver can obtain the clock accuracy is about nanosecond or sub-nanosecond by using GPS precise satellite orbit and clock error data. Correspondingly, time comparison using PPP can attain this accuracy under the IGST.Compared with GPS Common-View (CV), PPP need not observe the same satellites in the sky. Therefore, PPP can accomplish time compare in any time and in any place in theory. Compared with GPS All-in-View (AV), PPP uses carrier observation data which is more accurate than code observation. Moreover, PPP is more flexible and lower cost than other time transfer methods.In this paper, we make intensive study on PPP, analysis the error elimination, realize the time comparison algorithm, smooth the result, and discuss the atomic clock prediction. The main content are as following:(1) PPP time comparison algorithm realizationTo achieve the centimeter accuracy for parameter estimation, more precise model must be used to correct the error while PPP is used to transfer time. And some residual error which are can not be neglected must be estimate as unknown parameter. The error resources and correction model are discussed in detail and Kalman filter (KF) model to estimate the parameter is chosed. Meantime, Helmert variance estimation is used to adjuste the variances from the two-type observations. Then time comparison algorithm is realized. To study the model precision, short baseline and comparison methods are employed. Results from the two methods show that the model precision is about 0.1ns. Meantime, time comparison is computed for the four time links and the results is compared with IGS outcome. Finally we get conclusion that this algorithm can be used in the time laboratory.(2) Comparison data smoothingComparison data smoothing is one of the most important tasks in time transfer. Vondrak smooth method depends on the smooth parameter?. Through study on the four time links, we consider the empirical value of?is about 200?400. Considering the characteristic of PPP and AV, we propose combining the result from these two methods by using Vondrak-Cepek which is available method to smooth the time comparison data. Just as Vondrak method, Vondrak-cepek is determined by?and?, so we propose the empirical values of these two parameters. Because the Vondrak-Cepek method is valid, the H-master and Cesium clock data is combined using this model and ideal result is obtained.(3) Clock predictionClock prediction plays an important role in time transfer, time keeping and navigation. In this paper, the conventional methods for clock prediction including polynomial model, auto-regression model, spectrum analysis model and grey model are presented. Then we study the KF model in detail. Two methods to get the noise matrices are discussed. Classical KF is employed to predict the atomic clock; we find that classical KF is useful while there is no jump happened. But if there are jumps, KF become lower convergence, even more KF diverges. To deal with the problem from classical KF, wavelet KF and adaptive KFs are proposed. Finally, the combination models are studied which may improve the accuracy and stability. According to the combination characteristic, these models are divided into linear models and non-linear models. In the former, classic and optimal weight are present. In the latter, artificial neutral network is discussed as an example. Because IGS precise clock data has more accuracy, we use the data as example to confirm the models validation.