Research On The GNSS Satellite Clock Offset Real-time Determination And The Real-time Precise Point Positioning

Real-Time Precise Point Positioning(RTPPP)is a technology development of Precise Point Positioning(PPP)in real-time application direction.It not only has the advantages of PPP technology: simple and flexible operation,high precision,but also takes account of the effectiveness of data processing.The accuracy of dynamic real-time positioning can be improved from the meter level to the decimeter level,and that of the static real-time positioning can be raised to centimeters Level.It is the important development trend of Global Navigation Satellite System(GNSS)in realtime positioning.The key elements of the RTPPP system include the real-time precise products of server-side,the RTPPP technology of client side and the network layer of data streaming.Among them,the RTPPP technology verifies the accuracy of real-time products,is the foothold of the system application.The real-time precise satellite clock offset is an important part of real-time products,and is one of the key factors affecting accuracy of RTPPP.In this paper,three methods of satellite clock offset real-time determination and two methods of RTPPP are studied and verified by experiments,at the same time,the related core softwares are developed for achieving RTPPP.The main contents of the thesis are as follows:1.A new tracking station selection method based on the triangulated irregular network(TIN)is proposed in this paper.It's used to select evenly distributed tracking stations for real-time satellite orbit and clock offset determination.2.In this paper,three methods(undifference,inter-satellite difference,epoch difference)are propoesd to calculate the satellite clock offset in real-time.The results in GPS satellite clock offset calculation show that: the accuracy of the real-time satellite clock offset is about 0.18 ns with undifference method,about 0.2 ns with inter-satellite difference method,and about 0.17 ns with epoch difference method.The epoch difference method takes the shortest time,and the single epoch calculation of that takes an average time of about 0.15 s,which is very helpful for obtaining the real-time satellite clock offset by second update.3.In this paper,two methods of RTPPP are proposed: undifference RTPPP and epoch difference RTPPP.The results of the RTPPP simulation by after-observation datas show that: When using satellite clock offset products calculated by the undifference method,the positioning accuracy of undifference RTPPP is better than 8 cm,and that of epoch difference RTPPP is better than 10 cm;while using the satellite clock offset products calculated by epoch difference method,the positioning accuracy of undifference RTPPP is better than 3 cm,and that of epoch difference RTPPP is better than 6 cm.The epoch difference RTPPP,although the positioning accuracy of it is slightly weaker than that of the undifference method,but does not need to deal with a large number of ambiguity parameters,can directly use the clock offset between epochs,which can provide a new solution for real-time high-precision positioning.4.Four key softwares are independently developed for the realization of RTPPP,including real-time precise satellite orbit determination software,real-time satellite clock offset determination software,RTPPP software and real-time data stream processing software.At the same time,the functional modules and data processing flow of each software are introduced.5.The BDS data processing experiments which consists of satellite clock offset real-time determination and RTPPP are conducted.The results of BDS satellite clock offset determination show that: the accuracy of the real-time BDS satellite clock offset is about 0.3 ns under undifference method,while about 0.27 ns under epoch difference method;the results of the RTPPP show that: compared with undifference method,the epoch difference method to calculate the satellite clock offset for RTPPP has higher positioning accuracy.The positioning accuracy of BDS is better than 10 cm,while with GPS joining,the positioning accuracy has a significant improvement,and speeding up the positioning convergence.