Research And Software Implementation Of Precise Point Positioning Method Based On BeiDou Short Message Communication

Real-time precise point positioning(RT-PPP)is widely used in the field of marine highprecision navigation and positioning due to its advantages such as only single receiver,no base station assistance,and high-precision.Limited by Inmarsat’s high-cost communication fees,RT-PPP is difficult to meet the needs of marine mass applications.The emergence of BeiDou Short Message Communication(SMC)provides a new solution for high-precision location services in global seas.Therefor,how to use the low bandwidth and low frequency of short message communication to transmit State Space Representation(SSR)satellite orbit and clock correction messages to realize high-precision positioning is a problem that needs to be solved urgently for RT-PPP based on short message communication.In view of above problems,the main research contents of this article are as follows:(1)Taking real-time precise point positioning as the research object,the method of obtaining the SSR satellite orbit and clock correction messages,the information format and the method of use are studied in detail,and the result shows that the current BeiDou short message communication cannot transmit SSR messages in real time.Secondly,using SSR satellite orbit and clock correction messages and MGEX observation data to perform dynamic RT-PPP based on BDS/GPS,the results show that average error RMS value of East,North,and Up reaches 0.0458m,0.0286m,0.0605m respectively,which verifies that using the current analysis center’s SSR orbit and clock correction messages for precise point positioning can achieve centimeter-level positioning.Finally,the influence of the different update time SSR on the accuracy of the satellite orbit and clock and real-time precise point positioning is analyzed separately from the state domain and the positioning domain.A comparative analysis of the satellite orbit and clock data obtained after SSR correction and the post-precision products provided by IGS found that as the SSR update time increases within a short period of time,the accuracy of the satellite orbit and clock is changes slowly and shows a downward trend as a whole,and RT-PPP can still be achieved centimeter-level positioning accuracy.(2)Aiming at the low bandwidth of BeiDou short message communication that it is difficult to transmit SSR orbit and clock correctios,this paper proposes a newly SSR satellite orbit and clock corrections encoding method that suitable for short message communication,namely SMC-SSR,to achieve transmission of satellite orbit and clock corrections.The new SSR encoding method reduce size form the effective range of corrections,resolution size,and information encoding content,effectively reducing the SSR orbit and clock corrections of a satellite from the original 205bits～231bits to 68bits,which realizes the low bandwidth of short message communication to transmit large capacity SSR corrections.Aiming at the long delay of SSR orbit and clock corrections caused by the low communication frequency of SMC,this paper proposes a multi-card polling broadcast method to increase the communication frequency and keep the SSR update interval at 10 seconds to reduce the fluctuation of the positioning curve.Finally,using data of the MGEX to conduct real-time precise point positioning experiments based on regional and global short message communication.The experimental results show that RT-PPP based on short message communication can achieve decimeter-level or even centimeter-level positioning accuracy,which positioning accuracy is consistent with RT-PPP based on Internet.(3)In view of the real-time requirements of marine mass applications for high-precision navigation and positioning at this stage,this paper uses the Qt Creator platform to design and develop SSR data broadcasting software based on short message communication.And carried out the secondary development of the team existing real-time precise point positioning software.Combine the existing satellite navigation equipment in the laboratory for experimental testing.The test results show that the BDS/GPS real-time precise point positioning based on short message communication converges to within±0.3m in the east,north,and up components.Among them,the east error RMS value is 0.2352m,the north error RMS value is 0.0591m,and the up error RMS value is 0.1180m,which can achieve positioning performance consistent with RT-PPP based on Internet.