Research And Implementation Of Real-time GNSS Precise Point Positioning

Precise Point Positioning(PPP)is a technique based on a single GNSS receiver,which uses International GNSS Service(IGS)precision satellite orbit and clock products and accurately corrects various errors to achieve high-precision positioning.Compared with traditional differential positioning,PPP can better overcome the influence of baseline distance on positioning,reduce positioning cost and expand application range,and has important market application value.At present,PPP technology develops from single system and post-processing to multi-system and real-time applications.The consistency of PPP function model and stochastic model is the key to realize high-reliability and high-precision real-time positioning of PPP.After years of technical accumulation,research on the PPP function model has matured.However,faced with the complexity of signal propagation,the diversity of error sources,and the differences in precision product quality,how to accurately describe stochastic models and improve PPP accuracy and reliability are the problems that need to be solved in real-time PPP.In addition,multi-system real-time PPP software and hardware engineering is an important basis for the application of PPP technology.In view of the above problems,the main research contents of this paper are as follows:(1)The system expounds the basic theoretical knowledge of multi-system real-time PPP.The processing flow applicable to multi-system real-time PPP is summarized,by analyzing several typical PPP function models,the main error source processing methods and parameter estimation methods.Through actual tests,it is verified that multi-system joint has obvious advantages in navigation positioning accuracy and convergence time compared with single system.(2)From the perspective of the consistency between the guaranteed function model and the stochastic model,firstly,according to the propagation law of the error,the influence of the prior weight deviation on the reliability and positioning performance of PPP is theoretically derived.Through the actual data verification,when the weight deviation occurs in the stochastic model of the system,the navigation positioning accuracy and reliability are significantly reduced.Secondly,traditional high-angle stochastic model only considers the problem of the random error associated with elevation angles.This topic focuses on the evaluation of real-time precision satellite orbit and clock error,tropospheric delay and other major error,and more refined PPP stochastic model,which achieves the improvement of PPP accuracy and the guarantee of positioning reliability.In the end,Through the actual GPS test,compared with the traditional height angle model,the positioning accuracy improvement rates of the east,north and up directions can reach 10%?6%?1%.(3)In the multi-system stochastic model weight assignment,the Helmert variance component estimation is used to adjust the weight ratio between the systems in real time for the problem that the multi-system PPP function model does not match the stochastic model caused by the unreasonable system-to-system weight ratio,which can achieve the purpose of matching the function model and the stochastic model and ensures the reliability of the multi-system PPP.the positioning accuracy of the east,north and up dynamic directions significantly improved.At the same time,considering the influence of non-modeling error on PPP reliability and in order to improve the robustness of PPP,the IGG? model-based robust Helmert variance estimation method is adopted to reduce the weight of the gross difference measurement and achieve the suppression of the gross error of the observation,Effectively avoid the positioning abnormality caused by the gross error,and ensure the reliability of PPP.(4)In view of the application requirements of multi-system real-time PPP at present,this paper selects the hardware platform for the requirements of platform operation stability and dynamic navigation environment adaptability,and designs real-time processing software based on DSP to realize navigation and positioning,map data matching,etc.Through a large number of dynamic tests,system performance is stable,meeting the requirements of strong real-time,high-precision,high-dynamic navigation and positioning.