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Design of Clock Synchronization based on Wireless Clock Difference Negative Feedback for Independent Distributed Pseudolite Systems

For the distributed GNSS pseudolite positioning system with independent networking, it is difficult to provide a unified system clock by wire in some application environments. For the pseudolite system using the single-point positioning method, clock synchronization is very important to achieve the high-precision pseudolite positioning by using the carrier phase technique. In this paper, a clock synchronization scheme between pseudolite stations is designed and implemented by using carrier phase technology and clock difference wireless feedback. A clock monitoring station and its corresponding synchronization device are designed based on the master-slave pseudolite network structure, and the clock synchronization of the distributed pseudolite system is implemented by using the wireless feedback of clock difference. The clock monitoring station uses the GNSS receiver with dual-antenna to obtain the carrier phase observations, and a master-slave clock difference mathematical model based on the carrier phase technique, and the least squares estimation adjustment search (LAMBDA) algorithm to fix the carrier phase integer ambiguity to continuously obtain real-time clock difference between master and slave stations, and then the station broadcasts these clock difference data by wireless data transmission. The Slave pseudolite station processes these clock difference data according to the clock error control model, and converts it into corresponding control voltage to adjust the frequency of the voltage controlled temperature compensated crystal oscillator, and achieves the clock synchronization of the pseudolite system. Finally, the experimental verification shows that the clock synchronization accuracy of the pseudolite system can reach more than 10ns.