Research And Implementation Of The Acquisition And Tracking Algorithms For BOC Navigation Signal

The Global Navigation Satellite System(GNSS)serves many aspects of human society.With the rapid development and the growing applications of GNSS,people require higher positioning performance of GNSS.Binary offset carrier(BOC)modulation is a potential method to solve the problem of poor anti-interference ability and low positioning accuracy faced by traditional Binary Phase Shift Keying(BPSK)modulation,and thus has been widely used in the GNSS system.However,the autocorrelation subpeaks of BOC signal cause the acquisition and tracking ambiguity problem.As a result,there is a large error in the positioning results.Although most existing BOC signal acquisition and tracking algorithms can avoid the false acquisition of subpeaks to some extent,there are still some deficiencies in the universality and acquisition performance.In this thesis,the spectrum and autocorrelation characteristics of BOC signal are studied.Different from the existing acquisition algorithms,a novel acquisition algorithm for even order BOC signal is proposed.In detail,an auxiliary vector is designed to modulate the pseudocode signal.After that,a curve with three peaks can be generated by shifting and superposing the cross-correlation curve between the modulated signal and BOC signal.Then the three-peaks curve is combined with the autocorrelation curve of BOC signal to generate a single-peak curve,which enables the unambiguous BOC acquisition.By adjusting the auxiliary vector's generation method,this algorithm is immuned to the difference between the order of BOC signal and the type of subcarrier.The universality and the acquisition probability of the algorithm are also effectively improved.Using the above combining curve,a phase discrimination scheme of code loop for even order BOC signal tracking is designed.Since there are still some residual subpeaks of the combining curve,a method is proposed to eliminate the risk of subpeak locking.Specifically,when the tracking loop is locked,the relationship among the Early,Prompt and Late values of BOC autocorrelation curve will be checked to confirm that the locking point is exactly located in the main peak.Finally,the acquisition and tracking algorithms are implemented on the Field Programmable Gate Array(FPGA)hardware platform,and the parameter measurement algorithms are used to monitor the acquisition and tracking results to verify the effectiveness of the algorithms.