Analysis And Comparison Of Multi-mode GNSS Precision Single-point Positioning Accuracy

Precise point positioning(PPP)technology by a single station of GNSS receiver observation pseudorange observation and carrier phase observation value,using the related institutions to provide high precision satellite ephemeris,the satellite orbit and clock difference products,etc.,and through the model parameter estimation method of correction or careful consideration and satellite terminal,a receiver related in the process of the signal propagation and error influence on positioning,to calculate the position coordinates,receiver clock errors,tropospheric delay and other parameters of the station under the ITRF frame.The technology has high precision,flexible operation and is not limited by baseline length.PPP technology uses non-differential observation model,compared with the relative positioning of double-difference model,PPP technology in a wide range of mobile measurement(such as ground movement mapping,unmanned aerial photogrammetry,marine measurement,precision orbit determination of LEO satellite),the rapid solution of large scale network,precision timing,atmospheric science and geodynamics have unique application value.At present,the PPP technology of single GPS system has been mature,and a lot of research work has been carried out in multi-system PPP.With the construction and development of satellite navigation and positioning system,Multi-mode multi-frequency GNSS precise point positioning has become a hot research direction in the field of satellite navigation and positioning.However,the multi-mode multi-frequency combination not only brings opportunities,but also brings a lot of challenges.In view of this,this paper focuses on the multi-mode GNSS precise point positioning research,the main research work and conclusions are as follows:(1)On the basis of GPS PPP location model,the GNSS PPP location model of two-system,three-system and four-system combined mode is derived respectively.Four parameter estimation methods(least square estimation,standard Kalman filter,extended Kalman filter and backward combined extended Kalman filter)are discussed,and the GNSS PPP error correction model is studied.The theory and control method of GNSS data quality analysis are expounded.(2)Using a variety of GNSS data quality check software(TEQC/RTKLIB/Anubis),the quality check of the observed data in MGEX station and in different occlusion observation environment is carried out,and the quality of GNSS observation data under different observation environment is analyzed.The research work has practical reference value for CORS sites selection and GNSS data quality detection and so on.(3)The effect of different solution strategies on the performance of precise point positioning is analyzed,and the applicable methods of GNSS PPP processing strategy are summarized.(4)The multi-GNSS static/kinematic precision point positioning test is carried out by using the multi-system GNSS precision orbit and clock difference products provided by MGEX analysis center.The multi system GNSS precision track provided by MGEX analysis center.For static positioning,the GRCE combination can get relatively high positioning accuracy in a short time,the RMS values of static solutions of E,N and U in about 15 minutes are 7cm,3cm,8cm and 2cm in 30 minutes respectively.In kinematic positioning,when the cut-off angle is 40 °,GPS single system is difficult to meet the needs of location services,the E and N directions of the GRCE combination are limited compared with the GC combination,but the elevation was improved significantly,with an average improvement rate of about 25%.Although the direction of E and N is less obvious than that of GC,but the horizontal positioning accuracy can reach 5cm,and the elevation direction can reach 11 cm.(5)The positioning performance of BDS/QZSS satellite navigation system is evaluated.The positioning accuracy of static PPP combined with BDS and QZSS in E,N and U directions is higher than that of single BDS system.When the cut-off angles are 7°,15°and 30°,the positioning accuracy in U direction increases by25%~34%,and in E and N direction increases by 10%~13% and23%~34%,respectively.When the cut-off angle is 40 °,in the U direction,the BDS+QZSS combination system improves more obviously than the BDS singlesystem in the low cut-off angles(7°and 15°),and the positioning accuracy improves by more than 30%.In Kinematic PPP,the positioning accuracy,availability and reliability of BDS+QZSS combination system are improved more than that of BDS single system.When the cut-off angle is large(30°and 40°),the improvement rate of E and N direction positioning accuracy is about 10%~50%,and the improvement rate of U direction positioning accuracy is more than 50%.In the future,with the improvement of the satellite construction of Japan's QZSS system and the global networking of China's BDS satellites,the QZSS satellites will contribute greatly to improve the positioning accuracy,reliability,availability and stability of GNSS systems in areas such as cities,mountains,densely-packed buildings and severely covered areas.(6)The positioning performance of multi-mode GNSS PPP under different occlusion observation environments is analyzed.In different occlusion observation environments,the static PPP availability of GPS single system is about 30~85%,the epoch availability of GRCE combination is about 85~98%,the available epoch is about 8~170% higher than that of GPS single system,and the positioning accuracy of GRCE combination E,N and U is about 10~95%,6~85% and 2~95% higher than that of GPS single system respectively.Multi-system GNSS PPP in complex environment has good application value in improving positioning accuracy,convergence time,positioning stability and reliability,etc.