| Bei Dou Navigation Satellite System(BDS) is China’s second-generate satellite system that will be capable of providing positioning, navigation and timing services to users on a continuous worldwide basis. However, due to the fact that the electromagnetic environments become more and more complex and the satellite signals are susceptible to intentional or unintentional interferences, it is possible that sometimes the satellite navigation receiver can’t work normally. So it is important to improve the work performance of the satellite navigation receiver in the presence of interferences.Taking the Bei Dou satellite navigation as the object of study, the dissertation discusses the anti-jamming method in time domain, spatial domain and space-time domain. In time domain, an adaptive all-pass based notch filter is studied in which a modified Gauss-Newton algorithm that yields a variable convergence in every iteration is applied. The simulation results show that the modified Gauss-Newton algorithm can lead to both faster convergence speed and better anti-jamming performance. In spatial domain, the power inversion algorithm is studied. According to simulation results, how the anti-jamming performance varies with the number of antenna element, the input Signal to Jamming Ratio and the DOA of interference signals are analyzed. Supposing that the antenna has M elements, so the degree of freedom of antenna array is M -1 and up to M -1 interferences can be suppressed effectively. When the number of interference increases, more antenna elements are needed to guarantee that all interferences are suppressed successfully, which undoubtedly increase the size and cost of the system. Moreover, the power inversion algorithm has no resolution in frequency. To solve the above shortcomings, space-time adaptive processing technology(STAP) which can analyze the property of input signals in both spatial and time domain is discussed. By placing several delay units behind the antenna element, the degree of freedom of the antenna array can be greatly promoted and the STAP algorithm has resolution in frequency. According to simulation results, how the anti-jamming performance varies with the number of antenna element, the number of interference, the number of delay unit, the input Signal to Jamming Ratio and the DOA of interference signals is analyzed. The traditional anti-jamming method just suppresses the interferences without utilizing the feature of the satellite navigation signal and it may even weaken the received signal,which can influence the effect of the following signal acquisition and tracking procedures. Therefore, in the final part, a new algorithm based on Cross Spectral Self-coherence Restoral(Cross-SCORE) technology is discussed. Due to the repetition of PRN code of Bei Dou navigation signal, the Cross-SCORE algorithm which can generate high gains towards the direction of satellite and place deep nulls at the jammers location determines the weight vector of the beamformer by maximizing the cross correlation between the output of the array and a reference signal in the condition that the jammers are not cyclostationary. The Cross-SCORE algorithm has the advantage of generating high gains toward satellite signal without any prior knowledge of it. However, the Cross-SCORE algorithm needs a large amount of calculation because of eigenvalue decomposition operation. To reduce computational complexity, the adaptive Cross-SCORE algorithm is proposed and its performance is studied according to simulation results. |
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