Research On Differential Positioning Algorithm For BDS/GPS Pseudorange Virtual Observations And Software Implementation

The Global Navigation Satellite System(GNSS)uses BDS(BeiDou Navigation Satellite System),GPS(Global Positioning System),GLONASS(Globalnaya Navigatsionnaya Sputnikovaya Sistema)and Galileo(Galileo satellite navigation system)satellite positioning systems and their enhancements to provide global real-time,all-weather navigation and positioning services[1].At present,The Beidou three-generation navigation satellite system was independently researched and developed by China has provided positioning,navigation and timing services for the key areas along the "Belt and Road" in December 2018[2].The pseudo-range differential service is a high precision positioning service which has be used most widely.China's have established national and provincial CORS networks provide the infrastructure for real-time high-precision location services.With the development of high-precision positioning technology,the demand for high-precision positioning has gradually shifted from industry demand to mass demand[3-5].At present,the pseudo-range differential service is divided into two modes according to the type of the broadcast differential signal,which is the correction number mode and the observation mode.Mode for broadcasting pseudo-range corrections is not compatible with BDS because RTCM2.3 does not have a BDS definition currently.The mode of broadcasting observations needs to broadcast the coordinate information of the base station to the user at the same time that will result the leakage of the base station information,which is inconsistent with the relevant provisions of the current base station management regulations in China and it is not suitable for providing services on a large scale.Therefore,the traditional pseudo-range differential service mode can no longer meet the needs of current mass location services.This article carry out research on BDS/GPS pseudo-range differential positioning services relies on four provincial CORS networks in Hunan,Sichuan,Hebei and Heilongjiang.According to the current problems encountered in the pseudo-range differential positioning service,the network RTK virtual reference station(VRS)service method is used to generate the integrated pseudo-range correction number by using the CORS data,and then the virtual pseudo-range virtual observation value is generated which use for user Differential Location Service to solve the problem that the correction mode in pseudo-range difference service cannot be compatible with the BDS currently and the observation mode does not conform to the national secrecy regulations.A differential positioning service system based on BDS/GPS virtual observations was developed to provide the sub-meter and meter-level positioning services for the public and real-time vehicle test and experimental data analysis were carried out then got some useful conclusions.The main research contents and results of this article as follow;The differential positioning model of grid pseudo-range correction was derived,the virtual observation generation model was given and used Hebei CORS data to evaluated the accuracy of virtual observation generation.The main factors such as the base station density,the grid partition size and the virtual site elevation selection principle that affect the virtual observation value generation and service quality were analyzed by using the Hunan CORS network data.The optimal base density,optimal grid size and reasonable site elevation selection rules for the BDS/GPS grid virtual observation differential location service are obtained.The complete monitoring model of BDS/GPS pseudo-range virtual observations was derived.The Hebei data was used to verify the completeness monitoring method.The experiment proves that the completeness monitoring can effectively improve the validity of differential information and ensure the reliability of user positioning.The Receiver Autonomous Integrity Monitoring(RAIM)method based on fuzzy clustering analysis was deduced,and the algorithm was analyzed by using Hebei CORS data.The experimental results show that the RAIM algorithm based on fuzzy clustering analysis can quickly and effectively eliminate the observation gross error.The Hunan CORS data are used to test the pseudo-range differential positioning performance.The test results show that the BDS/GPS pseudo-range virtual observation value can provide the sub-level positioning service for the traditional terminal,and it is the smart meter-level positioning service.The position difference method considering the constellation configuration is proposed to improve the positioning accuracy of the smart phone.The actual test can provide the user with a plane better than 3 m and a vertical better than 5m positioning service.