Study On Acquisition And Tracking Methods And Performances Of Positioning In Software GPS Receiver

This dissertation studies the acquisition and tracking method in order to improve the performances of positioning in GPS software receiver.On the basis of introducing the GPS system structure and the composition of the satellite signals,the dissertation focuses on the optimization of the acquisition and tracking methods.The improved acquisition and tracking methods are implemented in the software GPS receiver in the end.An improved coherent-noncoherent acquisition method is presented according to the lack of the traditional GPS acquisition method in the weak signal. Because the traditional tracking methods are easy to lose lock in the weak signal, one tracking method based on extended kalman filter (EKF) is implemented. The key technical difficulties are seriously researched, and some relative optimizing techniques are also put forward.With the clear target, the GPS system structure and the composition of the satellite signals is introduced. Then, both the digital IF GPS signal simulator and the structure of software GPS receiver are analyzed. In signal acquisition, the principle of the traditional acquisition method is introduced, and then the coherent and incoherent acquisition methods are studied. Based on the analysis of the additional gain about the two methods, an improved coherent -noncoherent integration algorithm is presented. In the end, the performance of the acquisition algorithms is analyzed. In the GPS signal tracking, the PLL and DLL loop are introduced in detail. Then, the noise and multipath interference on the PLL and DLL loop are analyzed and the optimized EKF is introduced into the tracking loop .In GPS positioning, the paper focuses on the least-squares position method when there are more than four satellites in the sky.In the end of this dissertation, the field experiments are introduced for the performance testing of the improved receiver. The improved acquisition and tracking methods are written by VS2008 C\C++ language and embedded into the GPS software. Under the static positioning mode, the testing results show that the performance of positioning in the new receiver is improved effectively. These performance parameters are demonstrated to be satisfied with design requirements.