Research On Narrowband Inrerference Suppression Technology For Direct Sequence Spread Spectrum System

Direct sequence spread spectrum communication systems is widely used in various military and civil communication and navigation systems due to its advantages of anti-interference,anti-noise,anti-multipath fading,strong confidentiality,multi-access multiplexing and high-precision measurement.Its inherent spread spectrum gain makes it resistant to narrowband interference.However,in engineering practice,due to factors such as RF bandwidth,transmission/receiver complexity,and implementation cost,the increase of spread spectrum gain is limited.Therefore,spread spectrum systems generally have certain interference tolerances.Once the strength of the narrowband interference in the spread spectrum system is too high,the BER performance of the system will be seriously deteriorated,and reliable transmission cannot be guaranteed.In order to further improve the ability of the direct sequence spread spectrum system to resist strong narrowband interference in the case of limited spread spectrum gain,further measures are needed to introduce a special narrowband interference suppression module.Based on the research on the theory and characteristics of direct sequence spread spectrum signals,this paper introduces various narrowband interference suppression techniques and compares the advantages and disadvantages of different technologies.The frequency domain real-time filtering technology based on Fourier transform has been widely studied and followed because it has the advantages of interference intensity,number of interference,and insensitive frequency.In addition,due to the existence of FFT algorithm and large number of points,high-speed FFT chip technology is quite mature,the frequency domain real-time filtering technology is the most likely to be the first to realize the application in practical engineering.Therefore,this paper focuses on the real-time filtering technology in the frequency domain.Based on this research,a frequency domain real-time filtering algorithm for spectrum segmentation is proposed.The algorithm uses the idea of spectrum segmentation,and selects the threshold by sorting to detect the disturbed spectral lines in the spectrum.At the same time,the sum of the absolute values of the real and imaginary parts of the frequency domain sequence is used to calculate the threshold and reduce the complexity of the algorithm.The simulation results show that in the data transmission system based on 64-Walsh code direct sequence spread spectrum,compared with the existing narrow-band interference suppression algorithms in real-time frequency domain filtering,the frequency domain real-time filtering algorithm based on spectrum segmentation has better narrowband interference suppression effect,and the performance of the fr-equency domain real-time filtering algorithm of spectrum segmentation does not deteriorate even when the spectrum is uneven due to an increase in signal-to-noise ratio.Moreover,in the absence of interference,the useful signal is not substantially damaged,which makes up for the shortcomings of the existing frequency domain real-time narrowband interference suppression technology which is not well suited for systems with small spread spectrum gain.