Research On Interference Mitigation Techniques In GNSS Receivers Based On Transform Domain

The applications of Global Navigation Satellite System(Global Navigation Satellite System,GNSS)are almost everywhere in our daily life,but as Glen Gibbons says,"Your signal is my noise",the practical receivers are facing a variety of intentional or unintentional interference.Thus,adding a specific anti-jamming module in the navigation microprocessor becomes more significant,so that it can offer a better use of the weak navigation signal.Taking into account of the uncertainty of interference signals in time and frequency,the fractional Fourier domain interference mitigation algorithms as well as the wavelet domain interference mitigation algorithms are analyzed in this paper.The contents are as follows:Firstly,some common interference models are introduced,including narrowband interference,LFM(Linear Frequency Modulating)and pulse interference.The basic principle and traditional methods of transformed domain interference mitigation are introduced.Especially,receivers based on the transformed domain adaptive filtering are analyzed in detail.Then,on the basis of the transformed domain interference mitigation algorithm,the method to eliminate the LFM interference in the fractional Fourier transform domain is studied.The adaptive filtering in the fractional Fourier transform domain is proposed to be used in the interference mitigation method.Because of the special relation between Fourier Transform and the fractional Fourier Transform,a combination of the two algorithms is given and studied.The simulation results show that the proposed algorithm performs better than the traditional one in the condition of multiple or wideband interferences.Finally,the wavelet-domain anti-jamming methods are studied.The basic theory of wavelet transform and wavelet packet transform are introduced,and then the traditional wavelet domain anti-jamming algorithm is given.The adaptive wavelet packet transform interference mitigation method and simple interference mitigation method are introduced.Then again,the use of convex combined LMS adaptive filtering is proposed in the wavelet domain for interference cancellation.The basic principle of the convex combined LMS adaptive filtering and the algorithm's computing process are given.The simulation show that,compared with the single LMS filtering algorithm in wavelet domain,the proposed algorithm has better anti-jamming performances.