Loran-c Receiver Anti-jamming Technology Research

With the development of digital technology,digital Loran-C receivers have quite obvious advantages over analog receivers.Therefore,developing digital Loran-C receivers has been the inevitable trend at present.In this dissertation, the ways of restraining the interference and noise,which exist in signals received by Loran-c receivers were researched.An introduction is given,which is about domestic and overseas development on Loran-C navigation system and the composing of Loran-C system,and a general introduction on the structure of receivers and theory algorithm is also given in this dissertation.The interference and noise existed in receivers and corresponding ways of wipping of them is introduced in detail.At first,because of the relationship between Loran_C signal band width and signal sampling ratio,common FIR filters need many taps to realize the function of bandpass-filtering and heavy computational workload.According to this,a.way of designing efficient bandpass filter is brought forwardSecondly,although direct-current signal caused by impedance not matching among circuit board passes through bandpassfilter,it can generate new direct-current signal as a result of abandoning some bits.Also, the existence of direct-current signal has serious effect on detecting zero-crossing. So a way of restraining direct-current signal is given.Thirdly,a way of restraining corss-rate interference is given according to the source of corss-rate interference and the difference between chains.Finally,narrow band interferences is introduced and also making restraint on narrow band interference and noise by means of LMS and RLS adaptive algorithm,moreover, Way of estimate-counteracting and notch filter to restrain narrow band interference. is put forwardAll ways which has been existed in this thesis are simulated in Matlab,and bandpass filters,restrain direct-current,classical adaptive filters and notch filters are implemented recuring to FPGA.