Unambiguous Synchronization Method Of BOC Signals Based On Reference Waveform Design

The Global Navigation Satellite System(GNSS),as a major space information infrastructure,can provide worldwide high-performance positioning,navigation and timing service(PNT).With the generalization of GNSS application scenarios,diversification of service requirements,modernization of navigation systems,and increased categories of navigation signals,compatibility and performance of GNSS signal design constraints have become prominent.Binary Offset Carrier(BOC)modulation signal achieves spectrum shift of modulated signal by multiplying wave subcarrier with the legacy signal.Compared with traditional Binary Phase Shift Keying(BPSK)modulation,it can not only improve system compatibility,but also provide better code tracking accuracy and anti-multipath performance.Therefore,BOC signal is widely used in modernized GNSS systems.However,due to the existence of multiple sub-peaks in the autocorrelation function of BOC signals,the traditional synchronization methods will lead to ambiguities,which will resulte in a huge bias in the positioning solutions.Therefore,eliminating the ambiguity of acquisition and tracking in the synchronization process of BOC modulated signal is the key to the BOC modulated signal processing.The existing methods of unambiguous synchronization of BOC signals have the following disadvantages: the acquisition sensitivity and tracking accuracy degrade dramatically,the tracking accuracy of the cosine synchronization method is significantly lower than that of the sine BOC modulated signal synchronization method,and the complexity of the existing unambiguous synchronization method is high.In this thesis,regarding the issues above,the unambiguous synchronization methods of BOC modulation signal are studied.A method of acquisition and tracking without ambiguity for sine and cosine BOC modulation signal is proposed.This method is based on the fact that the autocorrelation function of BOC signal is piecewise linear function.An unambiguous acquisition method for sinusoidal BOC modulation signals is designed based on the periodicity and even-odd symmetry of BOC signal subcarriers.Based on the weighted combination of discriminators(WCD),a high-precision unambiguous tracking method for cosine BOC signal is proposed.A low complexity unambiguous tracking method based on Discriminator via Product of Autocorrelation and Cross-correlation(DPAC)for sine BOC modulation signal and a low complexity unambiguous tracking method based on Discriminator via Product of Cross-correlations(DPC)for cosine BOC modulation signal are proposed respectively.The main contents of this dissertation are indicated below:(1)A theoretical model for designing unambiguous correlation function based on combined correlation function is proposed.This method is aiming at the high cost of acquisition sensitivity and tracking accuracy of BOC signal synchronization method in eliminating ambiguity.Under this model,to improve the acquisition detection probability and tracking accuracy,a set of acquisition and tracking methods for sine and cosine BOC modulation signals are proposed.By linearly weighting the autocorrelation function(ACF)of BOC signals with different delays,a correlation function without ambiguity is obtained.In order to eliminate the non-zero cross-correlation of the above correlation function outside one chip and satisfy the non-coherence requirement,this method achieves a non-ambiguous non-coherent correlation function by multiplying the correlation function with ACF.The theoretical analysis and simulation results show that under the condition of Additive White Gaussian noise(AWGN),the performance of this method is improved obviously in detection probability,code tracking accuracy,and code tracking threshold.It is an excellent implementation scheme for high precision and high sensitivity receiver of both sine and cosine BOC modulation signal.(2)An unambiguious acquisition method for sine BOC modulated signals is proposed to address the problem that the existing unambiguous tracking methods for BOC signals can not take into account for both sensitivity and complexity.Based on the periodicity and parity symmetry of the subcarrier of BOC modulated signals,a pulse signal is designed as a local reference signal.By multiplying the cross-correlation function between the signal and the BOC signal and the correlation function of the truncated BOC signal,the correlation function which can realize unambiguous acquisition is obtained.Compared with the existing methods,this unambiguous acquisition method has low complexity,fast search speed and excellent detection probability.It has obvious application value especially under the condition of limited complexity.(3)A tracking model based on weighted combination of discriminators functions(WCD)is proposed to address the issue that the tracking accuracy of the existing unambiguous tracking methods is worse than that of the same order sinusoidal BOC when applied to cosine BOC signals.By combining the newly proposed high-precision quasi-unambiguous tracking method with the existing large traction range unambiguous tracking method,an unambiguous tracking method for the cosine BOC signal is realized.The former’s role is to ensure that the combined method has high-precision and the latter’s role is to eliminate the former’s ambiguous residuals.The weighting coefficients and correlator spacing of the two are obtained by optimizing accuracy.The theoretical analysis and experimental results show that compared with the existing methods,the proposed method greatly improves the tracking accuracy of the cosine BOC signal without affecting the multipath performance.The cost is increased complexity.The above WCD-based unambiguous tracking method is a very effective unambiguous tracking method for high precision requirements of cosine BOC signals.(4)A tracking model DPAC is constructed by multiplying the autocorrelation function and the cross-correlation function to construct the discriminant curve.This method is proposed to solve the problem of high complexity of existing BOC signals unambiguous tracking.The extended step signal model is used as the design method.An unambiguous tracking method for sine BOC signals and a quasi-unambiguous tracking method for cosine BOC signal based on DPAC model are proposed,and through the optimization search,an unambiguous tracking method based on the DPC model for the cosine BOC signal is proposed.Compared with the existing methods: DPAC-based sine BOC unambiguous tracking method reduces the number of correlators by 75%,and the DPC-based cosine BOC unsmbiguous tracking method reduces the number of correlators by 50%,greatly reducing the unambiguous tracking complexity.Under the multipath environment: the above two unambiguous tracking methods have obvious advantages in anti-multipath performance.The DPAC-based sine BOC unambiguous tracking method and the DPC-based cosine BOC unambiguous tracking method are very effective synchronization methods in complexlimited and strong multipath environments for sine BOC and cosine BOC modulated signals,respectively.