Research On Loran C Signal Interference Suppression Method And FPGA Implementation

Loran-C system can be used as an effective backup of the satellite-based navigation timing system because of its advantages of wide coverage and strong anti-jamming capability,and is an important part of the national PNT(positioning navigation timing)system.The development of high performance Loran-C receiver is of great significance,and the anti-jamming technology of the received signal is one of the key technologies to improve the receiver performance.In this paper,we focus on the interference suppression technology of Loran-C receiver signal in complex interference environment.The details are as follows:firstly,This paper introduces the theory of Loran-C signal characteristics and interference suppression,and designs an interference suppression scheme using a bandpass filter to suppress the out-of-band interference signal,and a bandstop filter and an LMS adaptive filter to filter the in-band interference signal;and introduces the principles and design methods of the FIR filter,IIR filter and LMS adaptive filter used in this paper.Then,a simulation study was conducted on the specific methods of Loran-C signal interference suppression,including a comparison of FIR filters and IIR filters for out-of-band interference bandpass filtering,and finally the FIR filter with linear phase characteristics was selected.The in-band interference frequency search is carried out by dividing the spectrum of the standard Loran-C signal to find the frequency of the in-band interference.The IIR bandstop filter and the LMS adaptive filter are compared for the filtering of in-band interference,and the LMS adaptive filter is chosen to have less impact on the signal time domain.Finally,based on the results of the above study,suitable in-band and out-of-band filtering algorithms were selected for the FPGA implementation of the Loran-C signal interference suppression algorithm.For the out-of-band interference,a FIR bandpass filter was used,and for the in-band part,an LMS adaptive filtering algorithm was selected.After the interference suppression algorithm was implemented,the signals before and after the interference suppression were compared in the time domain and frequency domain to verify the effectiveness of the hardware implementation of the suppression algorithm,and the interference suppression of the Loran-C signal was achieved.