Research On Ionospheric Correction Technology Of Dual-frequency And Multi-constellation SBAS

The global navigation satellite system(GNSS),as the main navigation method,has developed quite maturely.In order to improve the performance of GNSS,all countries are studying their own satellite-based augmentation systems(SBAS).As the main error source of SBAS,the existence of ionospheric delay makes it difficult to achieve the goal at the beginning of SBAS design.With the development of SBAS from a single-frequency single system to a dual-frequency multi-system(DFMC SBAS),DFMC SBAS has attracted attention because of its ability to better correct ionospheric delay.Therefore,in order to enable the navigation system to provide more accurate services,it is of great significance to carry out research on DFMC SBAS ionospheric correction technology.First,starting from the basic characteristics of the ionosphere in time and space,the related concepts of the ionosphere and the basic assumptions in the process of calculating the ionospheric delay are introduced,and the basic principles of ionospheric modeling are introduced.Starting from the principle,the ionosphere is explained.The effect of delay on GNSS signals,basic GNSS observations,mathematical models used to calculate ionospheric delay,and the data source of this topic.Secondly,through the analysis and research of the classic ionospheric delay correction model,using the collected measured data and the ionospheric products released by IGS,for different systems,the Klobuchar model and the grid model in the model method are used to calculate the ionospheric delay,and compare the results of the two models.Then discussed the choice of GNSS and SBAS for L5 signal and the significance of SBAS adopting dual frequency,and analyzed the difference between single-frequency SBAS L1 and DFMC SBAS L5 in message format and message content with WAAS as an example.The dual-frequency combination of GPS and BDS is used to calculate the ionospheric delay value,and the Klobuchar model and grid model are combined to compare and analyze the results obtained by the three solutions.Finally,starting from the error source of L1 SBAS,the error source of DFMC SBAS is analyzed,and the current and future WAAS integrity monitoring system structure is summarized.The horizontal factor of precision(HDOP)is used to solve the integrity parameter.The horizontal protection level(HPL)and the difference in the number of enhanced constellations,the theoretical analysis of the calculation of HPL when DFMC SBAS enhances a single constellation and enhances multiple constellations.