Research On Acquisition Algorithm For Weak BOC Signal

Now the Global Navigation Satellite System(GNSS) has been used in agriculture?industry, and GPS receiver has been widely used. However, as the GNSS's modernization and development, some problems have emerged: signal spectrum overlapping and serious interference between signals. In order to solve the problems, a new modulation —Binary-Offset-Carrier comes into being.Acquisition is an important part of the GNSS signal processing. Because of the ambiguity issue of the BOC modulation signals, the existing BPSK modulation signals' acquisition algorithms are not applicable for the BOC modulation signals. Besides, signals' SNR suffers from high-rise buildings?shelters?indoors and grand canyon so that GPS signals become very weak. The performance of conventional BOC acquisition algorithm is too poor, so the acquisition algorithms of the weak BOC signals become the problem that should be addressed.In order to realize the weak BOC signals' unambiguous acquisition algorithm, this paper includes three parts: the BOC signals' unambiguous acquisition, SNR accumulation algorithm, the weak BOC modulation signals' unambiguous acquisition algorithm.BOC modulation is studied and analyzed in depth. The spectrum and autocorrelation characteristics of BOC modulation signals and the related MATLAB simulation are studied. In addition, based on the principles and realization technology of the main two-dimensional acquisition algorithms of GPS receiver, this paper starts to research on the BOC signals' unambiguous acquisition algorithms. The simulation results show Autocorrelation Side-Peak Cancellation Technique(ASPeCT) has a better performance on ambiguity mitigating. So ASPeCT is used as the basis of the side-peaks eliminating techniques for BOC signal.In the research of the weak signals' acquisition algorithm, SNR accumulation algorithm is a key technology. In order to enhance the acquisition sensitivity, firstly, this paper analyzes the coherent integration, and combines the coherent integration with the noncoherent integration to eliminate the restrictions on coherent integration gain. Then the differential coherent integration, which can eliminate the square loss of the noncoherent integration, is proposed. Finally, this paper uses the energy envelope instead of the amplitude envelope in the differential coherent integration to enhance the acquisition efficiency and accuracy.According to the characteristics of the weak BOC modulation signals, the ASPeCT is transformed into the frequency domain by FFT to reduce the acquisition time and lay the foundation for SNR accumulation. This paper combines the improved acquisition algorithm with the improved SNR accumulation algorithm which forms the weak BOC modulation signals' unambiguous acquisition algorithm. The simulation results show this new algorithm is able to acquire the weak BOC signal which's SNR is less than-19 dB, reduce the average acquisition time and has better real-time and detection performance than ASPeCT-noncoherent integration.