Accuracy Analysis Of GNSS Long-baseline Real-time Precise Positioning And Time Transfer Based On IGMAS

Global Navigation Satellite System(GNSS),such as Bei Dou,provides users with navigation,positioning,and timing services and is increasingly important in national development and people’s livelihood.Precise Point Position(PPP)has become one of the hot technologies for wide-area precise positioning and timing services due to its advantages of high accuracy,flexibility,and no limitation on baseline length.However,real-time precise point positioning has problems such as heavy reliance on real-time satellite clock products with high-frequency updates,complex ambiguity fixing,and inconvenient multi-frequency applications.The international GNSS Monitoring and Assessment System(i GMAS)has built several evenly distributed domestic continuous operation tracking stations and provides real-time and post-processing observation data of the tracking stations to registered users free of charge.Among them,i GMAS Xi’an station is connected to the National Standard Time UTC(NTSC)signal.Based on the tracking station data provided by i GMAS and Bei Dou/GNSS multi-system precise forecast satellite orbit,the performance of long baseline double-difference real-time positioning and carrier phase precise common view(PCV)time transfer is explored and analyzed,which is expected to provide a long-range real-time precise positioning timing method different from PPP.Improving and enriching the wide-area highprecision real-time positioning and timing services is significant.The main research content of the thesis is as follows:(1)Analysis of multi-frequency multi-system long baseline real-time precise positioning performance.The coverage ranges of 500 km,750km,and 1000 km of i GMAS domestic tracking stations were analyzed.Based on 10 baselines ranging in length from the 400 km scale to the 7000 km scale,GNSS multi-system long baseline real-time static and dynamic positioning tests were carried out in three ways: dualfrequency ionosphere-free combined,dual-frequency non-combined,and triplefrequency non-combined,using rapid and ultra-rapid forecast orbits.The results show that the i GMAS domestic tracking station can cover most of the country within 500 km,especially the densely populated central-eastern region and almost the whole country within 1000 km.Combining the average positioning results of the test strategies,the accuracy and convergence times of real-time static and dynamic positioning are comparable to those of the posterior.Analyzed in terms of the average of the 8-day positioning results for multiple baselines,the BDS(Bei Dou Navigation Satellite System)real-time static positioning has an accuracy of 1.8cm in the horizontal direction,2.4cm in the elevation direction and a convergence time of 70 min.The real-time static positioning accuracy of GPS(Global Positioning System)is 1.9cm in the horizontal direction and 2.7cm in the elevation direction,with a convergence time of 45 min.BDS real-time static positioning accuracy is better than GPS,and the convergence time is longer than GPS;the dual BDS/GPS has the most significant improvement in GPS static positioning accuracy in the E(East)direction,37.5%,and the most significant reduction in the average convergence time of BDS static positioning,60%.The multi-system static positioning accuracy is comparable to that of BDS/GPS in the horizontal direction,better than 1.1cm,and the multi-system significantly improves the convergence time.The dual-frequency non-combined positioning accuracy and convergence time are better than the dual-frequency ionosphere-free combination.The real-time static positioning convergence time of the triple-frequency non-combined combination is better than the dual-frequency non-combined combination,and the convergence time of the dual BDS/GPS is reduced by about 15%.The average positioning accuracy and average convergence time of baselines of different lengths differs significantly.For baselines with lengths within 1000 km,the positioning accuracy of real-time static positioning is better than 1.8cm,1.0cm,and 2.4cm in the E,N(North),and U(Up)directions,respectively,with a convergence time of about 38 min.The positioning accuracy of real-time kinematic positioning is better than 2.5cm,1.9cm,and 5.0cm,respectively,with a convergence time of about 49 min.For baselines with lengths between 1000 and 2200 km,the positioning accuracy of real-time static positioning was better than 2.0cm,1.9cm,and 2.8cm in the E,N,and U directions,respectively,with a convergence time of about 50 min.In comparison,the accuracy of real-time kinematic positioning was better than 4.3cm,2.9cm,and 6.1cm,respectively,with a convergence time of about 63 min.The study results show that long baseline real-time precise positioning services can be carried out for users in the service area based on the i GMAS domestic tracking station.This service model is easy to implement,relies only on forecasted precise orbit products,and has good application prospects.(2)Analysis of long baseline carrier phase PCV time transfer performance.Based on 10 baselines ranging in length from the 400 km scale to the 7000 km scale and using orbit products from multiple centers,long baseline carrier phase PCV time transfer experiments are carried out for multiple GNSS systems and their combinations,involving both real-time and post-processing modes.The experiments are based on 33 consecutive days of observation data.The results show that compared with the PPP time transfer results,the BDS single system PCV time transfer accuracy is still better than0.6ns for baselines of length 7000 km based on precise products.In contrast,a single system cannot perform most of the time in GPS,Galileo(Galileo Satellite Navigation System),and GLONASS(Global Navigation Satellite System).For baselines with lengths of 3000 km and less,the accuracy of BDS-3 and GPS PCV results are comparable and better than Galileo PCV,while GLONASS PCV results are less accurate.The accuracy of real-time PCV time transfer based on precise products is comparable to post-processing PCV time transfer.For baselines with lengths of 3000 km or less,the accuracy of BDS-3 broadcast ephemeris-based PCV time transfer is within0.2ns,while the accuracy of the results based on GPS broadcast ephemeris,Galileo broadcast ephemeris and GLONASS broadcast ephemeris are around 0.5ns,0.4ns,and1.2ns respectively.PCV time transfer is not affected by the Differential Code Bias at the satellite end and can effectively avoid the discontinuity of the sky boundary caused by the clock products.The accuracy of the bi-directional filtering results is better than that of the forward filtering.The results show that the carrier phase-based GNSS PCV time transfer can achieve sub-nanosecond real-time/post-processing time transfer.The PCV time transfer mode is simple and inexpensive to implement,relies only on forecast precise orbit products,does not require real-time precise clock products,and is not affected by the Differential Code Bias at the satellite end,which has good application prospects.