GNSS Real-time Undifference High Precision Positioning Method

At present,the major satellite navigation systems have been widely used in various fields and become an indispensable part of the development process of each country.Due to the limitations of current technologies and systems,the enhanced system is still mandatory to achieve the high-precision real-time position information of centimeters or even millimeters.The non-difference PPP-based enhanced positioning technology is the current research hot spot.This paper aims to research and realize the real-time,high-precision and fast non-difference GNSS high-precision enhanced positioning technology for the real-time high-precision location service.Including the following aspects:Based on the in-depth study of PPP positioning model,this article discusses the reason why the non-difference ambiguity loses the integer characteristic.For the global or large-scale reference station network single-difference reference satellite datum is not uniform,the inter-satellite single-difference method is not applicable to the problem of estimating the satellite phase bias.A method for real-time estimation of satellite side Phase Bias for global or large-scale reference station networks is proposed.Through experimental analysis,the real-time estimated satellite wide-lane Phase Bias has a day-to-day stability,and the narrow-phase Phase Bias does not have this characteristic.Compared to the float solution,the real-time PPP non-difference ambiguity fixed solution accuracy improved by 22.6%,37.1% and 14.9% in NEU direction respectively.In order to restore the non-difference ambiguity which is easily to be affected by the satellite orbital clock error and the atmospheric unmodeled residual,the accuracy and stability of the Phase Bias of the satellite,a method of using the partial ambiguity resolution combined with "HOLD Phase Bias" is proposed.Through the analysis of experimental results,the method increased the fix rate of non-difference ambiguity by 30.5% to 99.3%.At the same time,it is found that the satellite Phase Bias estimated by the regional reference station could contain the unmodeled atmospheric residuals.The experimental results show that the PPPAR performance in each region is improved by using all the stations in each region to jointly estimate the satellite Phase Bias.In this paper,PPPAR is used to extract the non-difference atmospheric delay data of the reference station.On the basis of this,the hardware Phase Bias and relative ambiguity datum of different reference stations are different,which leads to the reference of the non-differential correction are different and cannot be verified by direct comparison.Hence the correctness of the non-difference correction data is verified by the "like double difference" method in this paper.Meanwhile,the regional enhanced PPP positioning is used to realize the instantaneous fixing of the non-difference ambiguity.The BDS-enhanced area-enhanced PPP non-difference ambiguity single epoch fixed technology was verified.The average positioning result of GPS in the same experimental environment is: N direction 0.034 m,E direction 0.034 m,U direction 0.075m;BDS+GPS The average positioning results of the dual system are: 0.033 m in the N direction,0.033 m in the E direction,and 0.077 m in the U direction;the single epoch fixed rates of the two modes are 99.1% and 99.58%,respectively.Aiming at the problem that the non-difference correction data cannot be directly used for RTK positioning,the equivalent transformation model of non-difference correction data and virtual reference station observation information is constructed.In parallel,the datum problem of non-difference correction is considered,and the virtual zero-baseline method is used to verify the generated virial observation.The correctness of the transformation method is verified by the positioning using the virtual observation of the RTK positioning(baseline length is about 70km).The NEU positioning accuracy is 0.012 m,0.009 mm,0.022 m respectively,and the fix rate is 94.1%.It indicates that the non-difference correction extracted from the regional enhanced PPP system and after equivalent transformation can provide equivalent service of virtual reference station like network RTK.A regional enhanced PPP positioning system is designed.The system includes a regional enhanced reference station computing unit subsystem,a satellite phase delay estimation subsystem,an enhanced reference station computing unit management subsystem,and a regional enhanced terminal user subsystem,wherein the reference station computing unit can directly fix the non-difference ambiguity independently and derive atmospheric delay by using the raw observation data and the know coordinates.Finally,the availability of the system is verified based on the field measurement data.