Research On Differential Feedback Clock Synchronization Between Pseudolites Based On Carrer Phase Technologies

In urban,suburb,underground and other complex environment areas,the Global Navigation Satellite System(GNSS)signals are often easily obscured resulting in a serious decline in positioning accuracy,and even unable to provide correct position services.To solve this problem,one of the main methods is to provide navigation signals by establishing pseudolite positioning systems in specific areas to effectively compensate for the signal blind areas of satellite navigation systems.In the distributed pseudolite independent networking positioning system,the clocks of the pseudolites are individual.Due to the different starting phases and the changes in the surrounding environment,a slight frequency offset and frequency shift are generated,which makes it impossible to synchronize the clocks of different pseudolites in the network.As a result,positioning cannot be performed,so the clock synchronization of each pseudolite is a necessary condition for the operation of the pseudolite system.In the clock synchronization problem of the pseudolite system,the clock error of the pseudolite is a critical factor that affects the positioning accuracy.For short-baseline measurement systems such as pseudolites,ranging errors caused by clock deviations have a more obvious impact on user positioning accuracy.Hence,it is necessary to monitor and predict the clock deviation of pseudolites in real time.Provide high-precision pseudolite clock deviation parameters,Through compensation and modulation,to ensure high-precision synchronization of the clock of the pseudolite system.This paper mainly completes the following research work :(1)Based on the analysis of the one-way time synchronization method,two-way time synchronization method and GPS common-view time synchronization method of pseudolites.Aiming at the problem of high cost and complicated algorithm for achieving clock synchronization.And needs for clock synchronization between different pseudolites in the network.Based on the carrier phase ranging technology,the characteristics of carrier phase and its extraction method are analyzed.A differential feedback clock synchronization scheme between pseudolites based on carrier phase is designed.It has the characteristics of relatively simple implementation and high clock synchronization accuracy.(2)According to the requirements of the clock synchronization scheme,a clock error algorithm scheme based on the difference between the pseudolites based on the carrier phase is proposed.The scheme adopts a master-slave pseudolite network structure,uses dual-antenna monitoring receivers,establishes a mathematical model according to the carrier phase observation equation,and calculates the relative clock difference between stations.It is verified by simulation that the synchronization accuracy of the clock difference algorithm using the difference between pseudolites can reach the order of nanoseconds.(3)According to the requirements of the clock synchronization scheme,analyze the GM(1,1)clock error prediction model.In view of its shortcomings,improvement methods are proposed.A dynamic gray pseudolite clock error prediction model(PFT-DGM model)based on power function transformation is established.The simulation verifies the effectiveness and accuracy of the PFT-DGM clock error prediction model.(4)According to the requirements of the clock synchronization scheme,four commonly used interpolation methods are simulated and analyzed,and a simple,efficient and high-precision piecewise linear interpolation algorithm is selected,and it is verified that it can meet the requirements of high-precision interpolation.(5)According to the clock synchronization scheme,using various algorithm modules,a simulation verification platform for the differential feedback clock synchronization between pseudolites based on carrier phase is established.Perform overall simulation verification on the clock synchronization of the entire pseudolite positioning system was carried out.The result proves the feasibility and correctness of the differential feedback clock synchronization scheme between pseudolites based on carrier phase.It has high synchronization accuracy and can meet relevant technical requirements.It can provide important technical support for the engineering design of pseudolite system clock synchronization.