Accuracy Analysis And Comparison Of BDS-3/GNSS Undifferenced And Uncombined Precision Point Positioning

With the successful global networking of our country’s Bei Dou Navigation Satellite System(BDS)in 2020,it marks that the Bei Dou system(BDS-3)has entered a new era of global positioning,navigation and timing services.It is the best time to develop and apply the BDS-3 to provide high-quality services to users around the world.The precise point positioning(PPP)in absolute positioning can achieve centimeter-level high-precision positioning on a global scale with only one receiver.Multi-system fusion positioning has more visible satellites and better satellite spatial distribution,which is conducive to improving positioning accuracy and accelerating convergence speed.It is the current development trend of precision point positioning.The undifferenced and uncombined positioning model uses the original observations,which can avoid the noise caused by the linear combination of the observations,and can be used to estimate the ionospheric parameters,or use the external ionospheric constraints to improve the positioning performance,which has important research value.Based on the above,this paper focuses on the BDS-3/GNSS undifferenced and uncombined PPP research,starting from the BDS-3 undifferenced and uncombined model construction,PPP program design,observation data quality analysis,PPP experiments,etc.The main research contents are as follows:(1)The relevant theoretical knowledge of GNSS precise point positioning is elaborated.The undifferenced and uncombined model of multi-system combined precision point positioning is deduced,the data processing strategy of single-system and multi-system precision point positioning is given,and the program of undifferenced and uncombined PPP experiment is designed by using RTKLIB and Visual Studio 2017.(2)The data quality of the BDS-3 is analyzed,including the number of visible satellites,DOP value,sky distribution of satellites,multipath effect value,Signal-Noise Ratio,etc.The RMS average and average convergence time of the single-day simulated dynamic and static positioning solutions for 8 stations including UCAL were calculated,the convergence judgment condition is that the positioning error in consecutive epochs is less than 1dm,and the static PPP single-day RMS average value is better than 5cm in the E direction,the N direction is better than 3cm,and the U direction is better than 6 cm.The E direction of the simulated dynamic single-day solution is better than 10.5 cm,the N direction is better than 9 cm,and the U direction is better than 12.3 cm.The static positioning convergence time is more than 30 minutes,and the simulated dynamic positioning convergence time is more than 50 minutes.(3)The undifferenced and uncombined precision point positioning experiments of dual systems and four systems are carried out,and the positioning performance is analyzed from three aspects: static PPP,pseudo-dynamic PPP,number of visible satellites and DOP value.The positioning performance of BDS-3/GPS dual system precise point positioning is the best,the three-dimensional error of static PPP is between 3-6 cm,the three-dimensional error of pseudo-dynamic PPP is between 9-15 cm,the convergence time of static PPP is about 25 minutes,and the convergence time of pseudo-dynamic PPP is about 40 minutes.BDS-3/GLONASS,BDS-3/Galileo dual system positioning performance is equivalent,the static PPP error of E,N,U three directions is between 7-10 cm,the three-dimensional error of imitation dynamic PPP is between 13-17 cm.The BDS-3/GPS/GLONASS/Galileo four-system combined PPP has better positioning performance than the dual system.The convergence time of the static PPP is shortened by 25%.The accuracy after convergence in the horizontal direction is within 3cm,and the convergence in the vertical direction is within 5cm.