Research On Enhanced Navigation Technologies Based On Low Earth Orbit Satellite

With the project of Integration of satellite and terrestrial communication systems being put forward in China,low-earth orbit(LEO)satellites play an extremely important role in space-based access network.In recent years,several large aerospace companies have also proposed large scale of LEO constellation to cover the world.On the other hand,although the global navigation satellite system(GNSS)has been developed for decades,the system still needs to be improved because of the characteristics of the high orbit and the low bit rate of navigation information transmission.Especially for China's Beidou Navigation Satellite System(BDS),the study of other auxiliary enhanced navigation function before established completely is indispensable.In fact,fast geometric position change of the low-earth orbit satellites and high speed data transmission provide the opportunity for the navigation enhancement research.In view of this,the positioning solution,code synchronization and integration of navigation and communication were studied in this thesis.The main research contents and achievements are as follows:(1)the problem of positioning and solving is introduced,which is based on the change of geometric position of low-earth orbit satellites.Firstly,the influence of low-earth orbit satellites on the morbidity of the observational equation is studied under the double-difference model.The STK software is used to simulate the morbid improvement in the scene.Secondly,based on the satellite orbit parameters provided by STK,the accuracy of solving the ambiguities of floating point solution based on genetic algorithm is analyzed,and a preprocessing method based on genetic algorithm is proposed.Finally,the solution performance of different orbital height of low-earth orbit enhanced satellites is analyzed by STK scene.From the simulation results,the low-orbit satellites can not only improve the morbidity of the observation equation,but also improve the accuracy of the baseline solution and the fixed-rate of the integer solution.With the orbit height decreasing,the effect is more obvious.(2)The thesis mainly studies the problem of code acquisition in the process of synchronization between navigation satellites and enhanced satellites.Firstly,a new code acquisition method based on frequency domain is proposed,and the representation of the cumulative phase and "correlation valley" are tried,followed by the corresponding acquisition performance simulation.The results show that the frequency domain processing method can achieve chip level capture.And then an integer decision method is proposed in the time domain followed by performance simulation.The capture accuracy in the time domain can be within 0.5 chips.(3)The thesis focuses on the integration technologies.In this thesis,we first propose an enhancement method of system fusion,that is,the method of transmitting satellite ephemeris information based on the pilot channel of low-earth orbit communication satellite,including the operation steps and the insertion structure,and then the enhanced effect is given.Relative to the original rate of navigation messages,the rate increases in two orders of magnitude.Then,the fusion method in signal layer is introduced,and then the influence of the navigation signal and the communication signal in the mixed signal on each other is analyzed.