Research On The Optimization Technology Of Doppler Velocimetry In GNSS Receiver

The Global Navigation Satellite System(GNSS)has been widely used in many areas of society and people’s livelihood.Speed measurement is one of the important functions of GNSS receivers.The speed information obtained by the receiver can be used in many scenarios,Such as aerial gravity measurement,hydrological measurement,speed calibration of inertial navigation equipment,and vehicle control.The most widely used speed measurement method in GNSS receivers is Doppler speed measurement.There are many factors that affect the accuracy of Doppler velocimetry,such as the accuracy of Doppler frequency shift and the accuracy of the velocimetry model.Therefore,it is of great significance to consider the above factors to optimize the Doppler velocimetry technology.The main objective of the subject is to optimize the Doppler speed measurement method through the pre-processing of Doppler frequency shift observations and the speed measurement model.Finally,a complete GNSS receiver solution module is built based on the ZYNQ hardware platform,and the speed measurement optimization scheme is implemented in the receiver.The navigation solution module of the aircraft verifies the actual speed measurement effect of the speed optimization scheme on the receiver.The main work of the thesis includes:First,based on the characteristics of GNSS observation data,the basic principles of positioning and velocity measurement are analyzed.Based on the principle of pseudo-range positioning and Doppler velocimetry,the positioning equations and velocimetry equations are constructed;the difference between the solution of the dual GNSS system and the solution of the single system is analyzed,and the positioning and velocity measurement equations of the dual system are given.Based on the dual system positioning and velocity measurement equations,the solution flow of the least square method is derived.It provides a theoretical basis for the subsequent design of the Doppler speed measurement optimization scheme and the design of the receiver navigation solution module.Secondly,the original Doppler and carrier phase GNSS observations are used to design a Doppler frequency shift preprocessing scheme to improve the speed measurement accuracy.Analyze the error sources of pseudo-range and Doppler observations of GNSS receivers and provide correction methods;Calculate the carrier phase by the central difference method to derive Doppler,and consider the effect of cycle slip;In-depth analysis of the accuracy differences and applicable scenarios of original Doppler and derived Doppler;Based on the Kalman filtering principle,the original Doppler and the derived Doppler are pre-processed respectively.Based on this,a combination of original Doppler and carrier phase observations is used to propose Doppler frequency shift preprocessing combination scheme.Thirdly,for the strong maneuverability of horizontally moving carriers on the surface of the earth,such as cars and ships,in consideration of the turning motion of the carrier,an EKF speed measurement scheme based on the Constant Turn Rate and Velocity(CTRV)model is designed.Analyze the difference between the linear motion model and the curved motion model,and give the model’s state prediction formula.The CTRV model in the curve motion model is used as the carrier’s motion prediction model.Based on this model,the extended Kalman filter speed measurement algorithm is designed,and an improved scheme is proposed to make it suitable for motion states such as straight lines and turns.Using the satellite navigation simulator to output the original observations of the state of horizontal turning movement,the simulation comparison of static and horizontal turning speed measurement is completed.The simulation results show that under high-speed turning conditions,the CTRV model reduces the speed measurement error by more than 80% compared to the constant speed.Finally,based on Xilinx’s ZYNQ7000 platform,a receiver navigation solution module is designed,and an optimized solution for Doppler speed measurement is implemented to complete the overall test analysis of the subject.The functional modules of navigation solution include message synchronization,check decoding,navigation information extraction,pseudorange calculation,and PVT(Position Velocity Time)solution.The navigation solution module can provide real-time positioning,speed measurement and timing functions,and the PVT information obtained can be output to the host computer designed by itself in real time through the NMEA-0183 standard format.The speed measurement effect of the speed measurement optimization scheme was verified through static and dynamic tests of the receiver.The test results show that the speed measurement optimization scheme significantly improves the speed measurement accuracy when the receiver carrier performs earth surface motion,especially when turning.