Theory And Application Of PPP-RTK Based On Sparse Network

GNSS Precise Point Positioning(PPP)is a GNSS positioning technology developed in the 1990s,which integrates the advantages of single point positioning and relative positioning,but compared with the popular real-time Kinematic(RTK)positioning technology,the convergence speed and accuracy of PPP is still far less than RTK,especially after the emergence of network RTK technology.Because of many errors,which in PPP can not be completely eliminated,lead to that the integer characteristic of the ambiguity is destroyed,and finally PPP can only get float solution.This greatly limits the development of PPP,because in reality most of users need fast,dynamic and high-precision solution,so the study of PPP fast ambiguity resolution is necessary.PPP-RTK is the technology of PPP ambiguity resolution,and a set of server and client system based on PPP-RTK is developed in this paper.The main work of the paper is as follows:(1)In the PPP-RTK server,the Fracional Cycle Bias(FCB)estimation method is introduced in detail,and has compared with the FCB products published by Wuhan University(WHU).Before the comparison,the benchmark conversion is required to correct the deviation of 0.47*n cycles on some satellite end FCBs.The results show that the deviation of the single-difference wide lane FCB is within 0.03 weeks,the RMS of the single-difference narrow lane FCB is 0.035 weeks,and the deviation within 0.05 weeks is 44.1%,and 81.1%within 0.1 weeks.Above all,it indicates that FCB solution software at the server can accurately estimate FCB products.(2)The reliability of PPP-RTK program at the client is verified.In the ambiguity float solution,the convergence time in static and kinematic PPP is 17.7 minutes and 29.3 minutes respectively.In the full ambiguity solution(FAR),time to first fix(TTFF)of ambiguity in static PPP is 27.3 minutes,and the accuracy of one hour float solution in E,N and U directions is increased from 3.62cm,1.27cm,3.71cmto 0.66 cm,0.72cm,2.61 cm,respectively.In the kinematic PPP,TTFF is 33.1 minutes,and the one-hour positioning accuracy of E,N and U is improved from 4.98cm,3.37cm,9.25cm to 1.34cm,1.06cm,3.20cm,and the improvement is all more than 60%.In addition,the results of the partial ambiguity resolution(PAR)show that TTFF is 23.2 minutes(static)and 28.3 minutes(kinematic),respectively,and the fixing rate is 90.4%and 87.0%,which is significantly optimal than that of FAR.All the results indicate that PPP-RTK program at the client is stable and reliable in all respects.(3)Considering that TTFF still need 20 minutes or more,in order to test the effects of the CORS on PPP ambiguity resolution,the real-time ionosphere and troposphere correction based on the regional CORS are delivered to the users to accelerate the fixing of ambiguities The experimental results show that after adding the regional atmospheric correction products,the ambiguity can be fixed within 1 second,and the positioning accuracy in E,N,U directions can achieve 0.1cm,0.9 cm,3.1cm.