Research On Unambiguous Acquisition And Tracking Of New Navigation Signals

New generation of navigation signals mostly adopt a data/pilot mixed signal structure,and with regard to the modulation,a new modulation scheme named BOC modulation is employed. Compared with the commonly used conventional GPS signals which are modulated by BPSK, new generation of navigation signals have been greatly improved in the acquiring and tracking performance. With the modernization of GPS and the building of the European Galileo system、Chinese Beidou satellite navigation system, new generation of navigation signals have a potential prospect. However,Navigation signals modulated by BOC have ambiguity in the process of capturing and tracking,which drives from its multi-modal autocorrelation function,limiting the widespread application of this modulation technique.Therefore, it has great important significance in researching on the elimination of ambiguity of new generation navigation signals in the process of acquisition and tracking,the main works are summarized as follows:Firstly, this paper analyzes the new generation of navigation signals from the aspect of signal structure and the modulation model. By analyzing the correlation property compared with the conventional navigation signals , it indicates that new generation of navigation signals have greater advantages. Then, a detailed description on the generating principle of BOC modulation signals and their autocorrelation properties、Spectrum Characteristics is given.For derived BOC modulation techniques such as AltBOC、MBOC modulation techniques are described in details, especially for the CBOC modulation signal which is one of the realization modes of MBOC modulation signals.After analysis on principles of navigation signal acquisition and tracking, this paper lists some methods of removing the ambiguity in the process of signal acquisition and tracking.then, carries out a detailed analysis on them from complexity and applicability aspect.Because of the pilot/data mixed structure of new generation navigation ,traditional method using single channel in signal capture will result in performance degradation under low SNR.This paper summarizes several pilot/data channel joint acquisition strategies, and two methods of eliminating ambiguity respectively based on sideband process technology and differential technology are proposed on this basis.Take Galileo E1 OS signal as example,Simulation results show that the proposed unambiguous acquisition algorithms have obtained the expected effect.To keep tracking precision of CBOC modulation signal and eliminate the tracking ambiguity,this paper proposes a tracking method based on a combination of correlation function and then designs the corresponding tracking loop. In this method, the autocorrelation function of CBOC modulation signal is dissolved and realigned, formating a new correlation function. The simulation results show that the new tracking method not only eliminates the ambiguity but also has some improvement in performance of thermal noise reduction and anti-multipath compared with the traditional tracking method .