Research On Improvement Of Grid Ionospheric Algorithm And Integrity Based On BDSBAS

With the continuous development of China's comprehensive national strength and continuous innovation and development in the science and technology industry,the Beidou Navigation Satellite system independently developed by China is gradually developing and is gradually being put into use.It is expected that the Beidou Global System will be fully completed by 2020.At that time,global users can enjoy the all-weather real-time and accurate satellite navigation and positioning services provided by Beidou Navigation Satellite.However,in some applications which requiring high positioning accuracy,such as the civil aviation field,the performance of the satellite navigation positioning system is not sufficient to Satisfy the navigation performance requirements of the aircraft's precision approach phase by itself.As the auxiliary augmentation system of Beidou satellite navigation system,the Beidou Navigation Satellite Based Augmentation System(BD-SBAS)has a significant improvement effect on the accuracy and integrity of the satellite navigation system.However,during the transmission of satellite signals from the space segment to the ground segment,the ionospheric delay error is the main source of error in the working operation of the Beidou Navigation Satellite Based Augmentation System.In order to further reduce the ionospheric delay error,this paper focuses on improving the positioning accuracy and integrity of the Beidou satellite navigation system,focus on improving the ionospheric delay algorithm based on the grid ionospheric model to improve the positioning accuracy and integrity performance of the Beidou Navigation Satellite system.The specific research contents are as follows:Firstly,introduced the basic theory of the Beidou Navigation Satellite Based Augmentation System,including composition,workflow,performance and so on.Then,focused on the ionospheric delay error during the transmission of satellite signals from the space segment to the ground segment.Based on the grid ionospheric model,improving the interpolation algorithm used to calculate the ionospheric delay of the penetration point.The ionospheric delay of the grid points is interpolated by quadratic surface fitting algorithm to obtain the ionospheric delay of the penetration point.compared with the ionospheric delay of the penetrating point obtained by the four-point interpolation method,the ionospheric delay of the penetrating point obtained by the quadric surface fitting algorithm is closer to the penetration point ionospheric delay obtained by the dual-frequency correction method.It shows that the correction effect of the quadric surface fitting algorithm on the ionospheric delay is more significant.Finally,based on grid ionospheric model,the ionospheric delay corrections can be obtained by different interpolation algorithms.explored the influence of the ionospheric delay corrections on the integrity.Calculate the vertical protection level(VPL)to measure the integrity of SBAS and analyze the results.On the basis of the optimized data,the three key RURA,UDRE,GIVE and VPL values of the integrity are simulated and compared,and the above simulation is analyzed in detail.From the simulation results,it is concluded that the results of UDRE,RURA and GIVE basically support the navigation services of the system at various stages of the aircraft.However,through the simulation results of the VPL,within the scope of the service of the BDSBAS,the BDSBAS cannot support the user-side(airborne side)to provide the APV-? class of flight-level navigation services,only can support the APV-? flight class of flight-level navigation services.