Research On GNSS Precise Point Positioning Augmentation Technology

Precise Point Positioning(PPP)technology could use a single Global Navigation Satellite System(GNSS)receiver to obtain the high precision position,atmospheric delays,clock offset,and other information all over the world.It has been widely used in precision timing,water vapor monitoring,seismic monitoring,precision orbit determination,and other fields.However,the slow convergence speed of traditional PPP technology limits its application in real-time high-precision positioning,timing,and other fields.In recent years,benefiting from the development of multi-GNSS,dense reference station networks,and Low Earth Orbit(LEO)constellations,multi-source information fusion can shorten PPP initialization time and improve the continuity and stability of the service.Based on this,this paper focuses on GNSS PPP augmentation technology,aiming to realize fast precise positioning data processing using multi-GNSS observation information,regional augmented information of reference stations,and simulated LEO navigation signal,supporting real-time high-precision positioning and timing applications.The paper mainly involves the Inter-system Bias(ISB)processing of multi-GNSS fusion PPP,the analysis of satellite-induced code bias(SCB)of Beidou-3(BDS-3),the regional augmented PPP technology under the condition of dense reference stations,and the LEO enhanced PPP technology.The main research contents and contributions of this paper are as follows:(1)The ISB and SCB of BDS-3 are systematically analyzed.Aiming at the inconsistency in the constant estimation strategy of ISB among multi-GNSS fusion PPP,the short-and long-term characteristics of multi-GNSS ISB PPP using precision orbit and clock offset products of different analysis centers are systematically analyzed,and the estimation strategy of ISB in multi-mode fusion PPP considering the characteristics of precision products of different analysis centers is proposed,which improves the positioning performance of the multi-GNSS fusion PPP.The characteristics of SCB of BDS-3 are analyzed using the observations of high-gain antennas,and the results shows that the variation of SCB of BDS-3 is around 0.1 m–0.2 m,which is much smaller than that of BDS-2.This indicates the enhanced anti-multipath ability of signals of the new system and provides the reference for the rational use of BDS-3 code observations.(2)A Single-Frequency(SF)PPP augmented technique based on the satellitespecific epoch-differenced ionospheric delay model is investigated.An SF PPP augmentation algorithm based on this model is designed.The positioning performance of GPS,BDS-2 single system,and GPS/BDS-2 dual system using this algorithm in different scale reference networks and their contribution to SF PPP positioning results are evaluated.The result showed that the difference in positioning result for GPS and GPS/BDS-2 between augmented SF PPP and DF PPP was less than 1 cm for the reference station network with an average distance of 34,139,and 172 km,and the difference of BDS-2 in more than 100 km reference networks was about 2 cm,which is significantly better than conventional SF PPP.This algorithm effectively improves the positioning performance of SF PPP and can obtain comparable solution results to DF PPP in a certain scale reference network.(3)A regional augmentation correction quality control method for regional augmentation in the observation domain is developed.Aiming at the characteristics of the comprehensive corrections in regional augmentation,a method is developed to identify the outliers by using the Median Absolute Deviation(MAD)method for the differential combination value of comprehensive corrections after inter-frequency difference and second-order inter-epoch and control the outliers by ambiguity reinitialization,weight reduction,or rejection for satellites using outliers.The method can effectively control the influence of outliers in augmentation correction on the positioning results and improved the reliability of the positioning results.(4)The augmented PPP technique in the state-space representation and its regional ionospheric delay modeling method are studied.The PPP-RTK algorithm based on atmospheric delays constraint is derived,and the ionospheric model established by the average latitude and longitude of Ionospheric Pierce Point(IPP)is developed.Compared with the existing inter-satellite single difference ionospheric model established by IPP(USM),the modeling requirements of this model are lower,and its interpolation accuracy is better than DIM(Distance-based Linear Interpolation Method)and USM.The model is applied to test the PPP-RTK performance on GPS single system as well as GPS/Galileo dual system in a reference network with an average distance of41 km from the reference station to the user station,and their fixed success rate of ambiguity was 68.8% and 96.3%,respectively,and TTFF(Time to First Fix)of the dual system was approximately 13 s.(5)The fixed ambiguity strategy based on LEO-assisted GNSS PPP is proposed and the contributions of LEO to GNSS PPP floating solution,PPP ambiguity resolution,and PPP-RTK are comprehensively evaluated using LEO satellite simulation observations.After the addition of LEO satellites,the convergence speed of the GPS、BDS single system,and GPS/BDS/Galileo/GLONASS combined system in PPP floating solution improved by 90.0%,91.0%,and 90.7%,respectively.For the PPP ambiguity resolution,the TTFF of the GPS single system and GPS/BDS/Galileo combined system was shortened by 86.4% and 82.8%,respectively.For the contribution of LEO to PPP-RTK in different scale reference networks,in the 57 km reference network,the fixed success rate of ambiguity of GPS/BDS/Galileo combined system increased from 86.8% to 94.9%,and the TTFF was shortened from 16.08 s to 10.16 s,with an improvment of 36.8%;In the 110 km reference network,the fixed success rate of ambiguity of GPS/BDS/Galileo combined system increased from 64.0% to 88.6%respectively and the TTFF of GPS/BDS/Galileo combined system was shortened from41.8 s to 28.4 s with an improvment of 32.1%.The LEO with GNSS fusion PPP algorithm effectively shortens the initialization time of GNSS PPP and accelerates the convergence speed of high-precision single point positioning.