Investigation On Iridium STL Positioning Method

With the increasing demand for navigation and positioning applications,disadvantages of global satellite navigation system such as weak signal strength and low information transmission rate come into being.The low-orbit satellite enhanced navigation system has gradually become a research hotspot because of its high information transmission rate,low signal attenuation and wide coverage.Satelles Time and Location(STL)system is currently the most successful low-orbit satellite enhanced navigation system,which can achieve independent positioning and timing.This thesis will study the positioning method of STL system.The Doppler positioning is used in STL system.This thesis analyzes the principle of Doppler positioning and the method of solving using the least squares,then deduces DOP of Doppler positioning through the solving process.Based on the simulation of the complete Iridium satellite constellation,this thesis verifies the solution method of Doppler positioning and comprehensively analyzes the positioning performance of STL system.The experimental results show that the STL system can achieve independent global positioning.The convergence time of the first positioning is about 8-10 minutes.The positioning performance is related to the latitude of the position where the receiver is located.And the higher latitude results in smaller positioning error.It can achieve tens of meters of positioning accuracy in mid-latitude regions,and can achieve positioning accuracy of more than ten meters in high latitudes.The positioning error of STL is proportional to the frequency measurement error of the receiver.On this basis,this thesis analyzes the method and solution of STL/GPS integrated positioning,and proposes to use the method of posterior variance estimation to determine weights between the two systems and then complete the positioning solution.Based on the application scenario that not enough GPS satellites can be observed,the feasibility of integrated positioning is verified by simulation experiments.Experiments show that compared with STL independent positioning,the convergence time of the first positioning of the integrated positioning is greatly shortened,which is less than 5 minutes.And the positioning accuracy is also greatly improved.The result proves that STL system can aid GPS to complete the positioning and obtain accurate positioning results when the observable GPS satellites are insufficient.