Research On The Key Technology Of Network RTK System To Improve The Availability

With the high-speed development of the GNSS,as well as the innovation of new wireless communication and Internet technology,many kinds of enhancement reference station network system based on GNSS become the research hot spot.Network RTK technology as a new local ground-based GNSS enhancement technique,with the advantages of high positioning accuracy,fast convergence rate and large measuring range,brings new change to the traditional differential positioning measurement model.In this paper,based on the independent developed of network RTK system,the all parts of the system are introduced.In allusion to improve the usability of network RTK system,there are three aspects of key technology to research and analysis in detail,which are the quaility of base station raw observation data?the way to fix the ambiguity and the service model of network RTK system.The main contents are as follows:(1)This paper briefly introduces the concept of network RTK system availability.The availability of network RTK system consists of base station raw data availability,communication link availability,data processing model availability,service model availability from the system module.In addition,it also consists of time and space availability from the system perfomence.Based on this,this paper puts forward the key technology to improve the availability of network RTK system.(2)Base station raw data quality monitoring.Ensure the quality of raw data the base station observation is the key to enhance the availability of network RTK system.Due to the base station environment or GNSS satellite fault occurs,all can lead to gross error original observation data in the base station or GNSS satellite ephemeris is not correct.According to the characteristics that the network RTK base station's coordinates are known,a method is proposed in this paper based on the iteration with variable weights to estimate the receiver clock error of the base station with hypothesis test to detecte and find the gross error.This method not only can detect and locate the false tolerance of pseudorange observations,but also can carry out fault monitoring of GNSS satellites.Through the processing of the actual base station data,it is shown that the method can monitor the raw observation data of the base station to ensure the usability of the raw observation data and improve the availability of the network RTK system.(3)The way to fix the ambiguity.Before network RTK system to provide users with stable and accurate service,there is a certain system initialization time.The shorter system initialization time can explain the network RTK system is more available.Fast fixed ambiguity is the most effective means to shorten the system convergence time.In this paper,two kinds of partial ambiguity resolution methods(PAR(Q)and PAR(A))are proposed by combining Bootstrapping method and least squares descent correlation(LAMBDA).The two methods use the method of calculating the success rate of Boootstrapping to select the ambiguity fixed subset,and then deal with the variance of the ambiguity floating solution and the ambiguity floating solution to complete the partial ambiguity fixed.The test results show that both methods can shorten the initialization time of network RTK system,improve the time availability of network RTK system,and ensure that the system provides users with stable and accurate service in time.(4)VRS and MAC conversion algorithms.The two service modes of network RTK system are compared and analyzed.In order to meet the users' demand for different service modes and improve the service mode availability of network RTK system,the mutual conversion method of these two service modes is proposed.Experiments show that the conversion algorithm of two service modes can correctly complete the mode conversion and provide users with accurate and stable navigation and positioning services,and enhance the availability of the network RTK system.