Study On The Acquisition And Tracking Algorithm For BOC And MBOC Modulation Signals

The satellite navigation technology is developing continuously, it has great strategic significance at the aspects of national economy, politics and military affairs, But they interfere with each other among the systems and the frequency band becomes more and more crowded.Under this situation, a new BOC(Binary Offset Carrier) modulation signal was proposed by European Space Agency, which solves the problems of coexistence and interference between different signals. MBOC(Multiplexed Binary Offset Carrier) is BOC derivative modulation, and it further enhances the code tracking accuracy and anti-multipath capability.On the basis of detailed describing the structure and properties of BOC and MBOC signals, then the acquisition algorithm of MBOC signal and the tracking algorithm of BOC signal are mainly studied. The main job of this thesis includes the following aspects:(1) Aiming at the ambiguity in acquisition of the TMBOC modulation signal caused by the multi-peaks of auto-correlation function, this thesis proposed an acquisition algorithm combining parallel code phase with fractal-reconstruction to remove ambiguity. First, it demodulates the received signal, then uses local PN code and BOC code to correlate with demodulated signal respectively. Next it takes the absolute value of the results and addition. Finally, it utilizes the fractal-reconstruction algorithm to fold a new correlation function without sub-peaks. Theoretical analysis and simulation results show the algorithm can capture the signal effectively with low complexity.(2) Aiming at the ambiguity in acquisition of the BOC/CBOC modulation signal caused by the multi-peaks of auto-correlation function, this thesis proposed an acquisition algorithm based on composition principle and its unique characteristics of auto-correlation function. First, it eliminates the effect of signal carrier frequency. Then according to calculation principle of BOC/CBOC correlation function, constructs two local signals to correlate with the received signal. Finally, according to the symmetry of the correlation results, it forms a new correlation function without sub-peaks by simple math. Theoretical analysis and simulation results show the new algorithm can effectively capture the signal and has higher main peak proportion, lower sub-peak proportion.(3) For a relatively narrow output frequency range of cross-product discriminator, doppler shift may not meet its tracking range after capturing the signal, this paper proposed an algorithm which uses Four-Quadrant Frequency Discriminator(FQFD) to assist two order frequency locked loop(2nd FLL) and three order phase locked loop(3rd, PLL) model. Firstly, frequency offset of the received signal is draw to the lower range by using the nonlinear characteristic of the Four-Quadrant Frequency Discriminator, and then uses the frequency locked loop to eliminate most of the dynamics, finally utilizes phase locked loop which has a characteristics of high tracking accuracy to realize the carrier tracking of high dynamic BOC signal rapidly and accurately. The theoretical analysis and simulation results show that this method increases about 300 Hz frequency range compared to the original tracking algorithm, simultaneously it has a good tracking performance.