Reseach On The Key Technology Of Pseudolite Navigation Based On Near Space Network Node

To achieve the navigation and positioning of Global Navigation Satellite System, it needs to observe enough numbers of satellites. Also, the geometric layout of satellites will affect the accuracy of positioning. When poor observation condition occurs, it will be difficult to meet users’ demand for precise positioning, or even cannot realize positioning. For the significant advantages in most aspects of near space platform, using aerostat to structure pseudo satellite constellation in near space, the accuracy of positioning can be effectively improved, which the military is particularly concerned about. For the characters like strong anti-jamming ability and flexible deployment of the near space pseudo satellite, it is capable of increasing numbers of visible satellites and improving the geometric structure of satellite constellation, which can fulfill the emergency positioning requirements in war, thus, the near space pseudo satellite reveals two major functions: first, it is able to replace satellite to carry out independent navigation and positioning when satellite is out of commission; second, it is able to strengthen GNSS and improve the accuracy of the whole system.Firstly, this dissertation studied the geometric layout of pseudo satellite constellation, and analyzed the impact of GDOP on positioning error. By simulating, how the changes of altitude angle and azimuth angle of pseudo satellite impact on GDOP is found out. Then I present three kinds of pseudo satellite layout scheme based on this, and according to the simulation results, their respective advantages and disadvantages are analyzed.Secondly, according to the structure, modulation and spread spectrum mode of the navigation satellite signal, and the characteristics of the near space pseudo satellite, this dissertation analyzed the similarities and differences between the pseudo satellite navigation message and GNSS navigation message, and simulated the pseudo satellite signal.Then the errors and key points of the pseudo satellite signal that exist in the propagation and positioning are analyzed in the dissertation. The corresponding solutions and compensation model to near-far effect, multipath effect and tropospheric delay are provided. The deviation brought by linearizing the nonlinear pseudo-range observation equation is also analyzed. And continuous common-view method is presented to solve the time synchronization between pseudo satellites. A simulation research on the issue of self-positioning of pseudo satellite by means of inverted positioning is made, and through pseudo-range double-differenced method, I get the error of the self-positioning of pseudo satellite by taking a pseudo satellite fixed on the ground as a reference station.This dissertation designed a GNSS/pseudolite dual-mode receiver and studied its baseband digital signal processing. FFT-based parallel code phase acquisition algorithm is used to implement signal capturing and code tracking loop and carrier tracking loop are designed to realize the subsequent calculation work, then the results can be used to research the improvement of positioning precision which brought by pseudo satellite.Finally, the enhancement of pseudo satellite to GNSS from the numbers, angle of altitude and angle of azimuth of pseudo satellite is researched. And with the CEP method, it directly displays that pseudo satellite is able to improve the accuracy of positioning.