Research On Code Synchronization Techniques For Binary Offset Carrier Modulated Signals

With the rapid development and wider application of global navigation satellite system(GNSS),it has gradually penetrated into civil and military fields,so that great demands are being placed on the provided services of navigation,position and timing.Therefore,in order to alleviate the contradiction between the limited spectrum resources and a increasing number of navigation satellites,a new generation of GNSS adopts binary offset carrier(BOC)signals,which can share frequency resources with traditional binary phase shift keying(BPSK)signal by spectrum separation.BOC modulation signal is to add periodic sub-carrier modulation to BPSK baseband signal.The increased sub-carrier modulation splits the main lobe of BOC signal’s power spectrum into two parts,and the main lobe width is smaller,which means that the accuracy of acquisition and code tracking for BOC signals is higher.However,sub-carrier modulation also generates multiple sub-peaks in auto-correlation function of BOC signals,which introduces ambiguity in the code synchronization.In addition,many problems inevitably arise in complex communication environments during the practical period,such as that lock point deviates in code tracking loop caused by multipath effect.Large Doppler shifts are inherent to high-speed relative motion between receiver and satellite and are likely to cause major problems during the code phase acquisition due to the introduced frequency ambiguity.In the case of strong interference,a serious distortion will be introduced in the time-domain waveform and spectrum of the received BOC signal,which makes it impossible to achieve the acquisition.Therefore,the above problems are studied in this dissertation,and its main work can be divided into the following three parts:(1)For the problem of ambiguity in the code synchronization for BOC signals,a dual-delay search acquisition algorithm,an ACF-decomposition-based acquisition algorithm and an unambiguous code tracking algorithm are proposed,respectively.For the dual-delay search acquisition algorithm,pseudo-noise code delay and sub-carrier delay are treated as two separate variables,and explicit expressions of the acquisition function are given in this dissertation.For the ACF-decomposition-based acquisition algorithm,this dissertation investigates that BOC ACF can be written as the convolution form of triangular pulse function and corresponding pulse train,and the acquisition function and structure are deduced according to the principle.For the unambiguous andmultipath suppressing code tracking algorithm,an ideal phase discrimination curve is designed first,and then a code tracking loop with superior performance and error-free locking points is obtained by correlating the local auxiliary weighting matrix with the local discrimination curve.The simulation results verify the effectiveness of three unambiguous algorithms,and demonstrate the comparison in performance with other algorithms,respectively.(2)It is difficult to accurately compensate Doppler frequency and Doppler rate of received BOC signals in the high-dynamic environment.Thus,an acquisition algorithm based on Discrete Polynomial-phase Transform(DPT)and PMF-FFT is proposed.Firstly,the received signal is ranked by DPT.Then,the order of high dynamic term in carrier is reduced.At last,the acquisition is achieved by PMF-FFT algorithm.According to the good aggregation ability of LFM signal in Fractional Fourier Transform(FRFT)domain,an improved acquisition algorithm based on DPT and FRFT is proposed.The model of high dynamic correlation result is established,FRFT is adopted to estimate the high dynamic items and to acquire the code phase.The complexity and performance of two algorithms are theoretically analyzed and deduced.The acquisition implementation diagrams and performance comparisons are given by simulation experiments.(3)For the problem of the difficulty in acquisition with strong interference for BOC signals,PMF-ap FFT algorithm is proposed by combining all-phase processing with PMF-FFT algorithm,which suppresses spectrum leakage and further enhances the performance.In the case of wideband interference,this dissertation uses a fast FRFT algorithm to suppress interference,which meets the requirement of the wireless communication system.Then PMF-ap FFT algorithm is adopted to capture the retrieved signal.In the case of narrowband interference,the interference position is determined according to the spectrum of the received signal,and an all-phase filter with arbitrary point notch is designed by adjusting the parameters.And then the acquisition of the received signal is achieved by PMF-ap FFT algorithm.At last,the effectiveness and the superiority of two algorithms are verified by simulation experiments.