Improving Positioning Accuracy Based On Multi-frequency And Multi-system GNSS

With the successful completion of the Beidou satellite navigation system networking,it began to provide global satellite navigation and positioning services,injecting new vitality into multi-frequency and multi-system GNSS.Multi-system multi-frequency RTK is the most widely used and rapidly developing technology in multi-system GNSS technology,while the emerging PPP-RTK technology has great potential and application scenarios in theory.However,there is currently little research on multi system PPP-RTK.This thesis will focus on the research of multi-system multi-frequency RTK and multisystem PPP-RTK.The main achievements of the thesis can be summarized as follows:1.Three frequency ambiguity resolution methods are studied:(1)The geometric free model TCAR method is simply studied,the idea and operation flow are introduced,and the ambiguity resolution results are verified by experiments.(2)In response to the shortcomings of traditional TCAR in solving ambiguity under medium and long baselines due to ionospheric delay,this thesis proposes a comprehensive TCAR method that takes into account ionospheric delay.Through experiments,it was found that the average solution deviation of this method under three medium and long baselines is under 3 circles,respectively.Moreover,there is little fluctuation between epochs under medium to long baselines,with the average value within 0.7 weeks.Compared to TACR,there is a significant improvement.2.This thesis studies the undifferenced error correction method in PPP-RTK model,briefly introduces the existing atmospheric error interpolation methods,and proposes a new method of ionospheric delay interpolation and elevation segmented tropospheric delay interpolation.Through experimental verification,the average absolute error of ionospheric delay is less than 2 cm,and the tropospheric delay error is less than 20 mm.3.We have conducted some research on the ambiguity resolution method for rover stations in the PPP-RTK model,and studied the error correction method for multi-system PPP-RTK considering inter system bias.4.The optimization algorithm proposed in this thesis was validated through experiments,and the accuracy improvement effect of multi-system combination positioning in RTK model and PPP-RTK model was compared.Discovery:(1)In RTK positioning,the BDS/GPS combination has a significant improvement in positioning accuracy compared to GPS and BDS single system positioning;(2)For PPP-RTK,the improvement of multi-system joint positioning accuracy is significant.The positioning accuracy of the BDS/GPS/Galileo joint model is much higher than that of the singlesystem,but it is not much higher than that of the BDS/GPS combination.(3)Compared to the classical error correction method,the error correction model considering intersystem bias has little absolute improvement in accuracy,but the improvement ratio is considerable: it can improve accuracy by 10% to 25% in the plane direction and 15% to35% in the elevation direction.