Design Of Clock Synchronization Based On Wireless Feedback For Distributed Pseudolite Systems

Due to the positioning principle and signal system similar to the GNSS,pseudo satellites have been widely used in the GNSS positioning enhancement and independent networking positioning by virtue of their high flexibility and high precision.For the pseudolite system using the single-point positioning method,because of the time of arrival principle,the synchronization accuracy of each pseudolite clock directly affects the measurement accuracy and has a crucial influence on the positioning performance.In the application of distributed pseudolite positioning system,each pseudolite clock is independent,and considering the cost factor,the pseudolite generally does not carry the atomic clock with high accuracy and high stability similar to the GNSS satellite,but uses cheap voltage controlled temperature compensated crystal oscillators as clock.Therefore,it is necessary to choose a reasonable system deployment method to accurately and quickly adjust the clock drift generated by the voltage controlled crystal oscillator.In some application environments,it is difficult for the independently distributed the GNSS pseudolite positioning system to provide a unified system clock in wired mode.In this thesis,a real-time clock difference monitoring station and corresponding pseudolite clock synchronization device are designed according to the technical requirements of pseudolite clock synchronization by wireless feedback and carrier phase technology,and the clock synchronization function of an independent distributed pseudolite system is completed.Firstly,according to the technical requirements of the clock synchronization system,the performance indicators of the pseudolite clock synchronization system are determined,and the network structure of the pseudolite clock synchronization system,and the functional architecture and synchronization mechanism of each part of the system are established.Moreover,the key issues related to distributed pseudolite clock synchronization such as 1PPS synchronization,wireless signal transmission,clock difference algorithm and clock offset control model are analyzed.Finally,the overall technical scheme and the technical scheme design of each functional unit are completed.Secondly,according to the key algorithms involved in the design of clock synchronization systems,the corresponding mathematical models are established and corresponding algorithms are designed.Aiming at the problem of obtaining the high precision relative clock difference of pseudolite,the carrier phase technology is used to construct the relative clock difference model,and the integer ambiguity and relative clock difference are solved by the dual-antenna receiver.Aiming at the problem of delay and coarseness in clock difference feedback control,GM(1,1)model and piecewise linear interpolation are respectively used to predict and interpolate the clock difference.Finally,the clock difference control model is designed to convert the clock difference of high sampling rate into a compensation voltage for the crystal oscillator,and complete system clock synchronization through wireless data link feedback.And then,according to the overall technical scheme of the pseudolite clock synchronization system,the software and hardware design of each unit module of the master pseudolite,slave pseudolite,and clock synchronization monitoring station in the synchronization system are completed,and the software and hardware cascade and debugging of each device are completed,preliminarily verifying the correctness and feasibility of the basic functions of the master pseudolite,the slave pseudolite,and the clock synchronization monitoring station.Finally,a system testing platform and a testing environment are built to test the clock synchronization accuracy of the distributed pseudolite clock synchronization system,and the stability and speed of convergence are evaluated.The synchronization accuracy of the1 PPS signal in the clock synchronization system is tested to verify its effectiveness for the positioning system.According to the initial frequency difference of the pseudo satellite in the system,the convergence region of the clock synchronization system is calibrated,and the convergence performance of the typical values is tested.The experiment shows that the pseudolite clock synchronization system can achieve time synchronization for pseudolite within the network,with a clock synchronization accuracy of better than 10 ns,a convergence speed of better than 120 epochs,and a 1PPS synchronization accuracy of better than 50 ns.All functions and performance meet the design requirements.