Research Of Narrowband Interference Suppression Technology For Beidou Satellite Navigation Receiver

Interference suppression technology has been the frontier of research about satellite navigation communication,and has been one of the key factors determining the success or failure of information warfare especially in the military field.Although Chinese satellite navigation system started late,yet it is developing rapidly.The continuous study about interference suppression technology will play an indispensable and influential role in the third-generation Beidou Navigation Satellite System(BDS).The navigation signals received by the receiver antenna are weak and vulnerable to surrounding electromagnetic waves and interference.Narrowband Interference(NBI)is a common type of interference for the receiver.It is necessary to add a module of narrowband interference suppression to the receiver,which can improve the performance of the receiver suppressing narrowband interference.This article mainly focuses on the algorithms of adaptively suppressing narrowband interference in time domain and frequency domain in depth,and an algorithm of adaptive threshold in frequency domain is selected for hardware implementation.Based on the satellite navigation signals received by the receiver mixed with noise and interference,this article mainly demonstrates the following aspects:(1)The article analyses spread spectrum communication technology used in satellite navigation system.Taken as an example,the direct sequence spread spectrum(DSSS)system is presented to simulate the BER curve before and after spread spectrum under narrowband interference.The results are compared and analyzed for their performance of suppressing interference.Then the mathematical models are given according to the structure of Beidou signal with narrowband interference,and the principle of navigation receiver and the theory of adaptive filtering technology are expounded.(2)The technology of time domain suppression narrowband interference is discussed from the perspective of adaptive predictive estimation.In detail,the Least Mean Square(LMS),Recursion Least Square(RLS)and the Improved Variable Step-size Least Mean Square(VSLMS)algorithm are described theoretically.The simulation results of each algorithm before and after the suppression of narrowband interference are compared,and the convergences of the algorithms are analyzed.The IIR trap is improved from the perspective of filter structure,and its simulation of before the improvement is compared with after the improvement.(3)The technology of suppression narrowband interference in frequency domain is studied from the perspective of adaptive threshold and parallel processing data.Firstly,it introduces the idea of frequency domain filtering,the reason of windowing function and the measures to reduce the influence.Then,it emphasizes the setting algorithm of adaptive threshold in frequency domain filtering,and makes the adaptive N-sigma algorithm improved.The simulations of suppressing narrowband interference are performed by the threshold ? value algorithm and the FBLMS algorithm for block processing data.Finally,the performances of suppressing narrowband interference,bit error rate curve,and implementation complexity of each algorithm are compared.(4)Considering the above simulation results and the algorithm difficulty of implement,the hardware implementation based on adaptive threshold ? value algorithm in the frequency domain is implemented.Firstly,it gives the system framework.Then,it designs the window function module,delay module,FFT core and interference suppression module in the system by Verilog.The design idea of the adaptive threshold in the interference suppression module is emphasized.Finally,the code is debugged online on the development board by means of the analysis tool.The validity of the selected algorithm is verified by checking the internal signal of the FPGA,observing and analyzing the waveforms before and after the interference suppression.