Research On The Narrowband Interference Suppression In DSSS System

Due to the fact that the direct sequence spread spectrum(DSSS)system is subject to the high power narrowband interference,which cannot be suppressed by the inherent interference rejection capacities,which is restricted by system bandwith,spreading gain and the complexity of the transmitter and receiver,this paper is devoted to a study on the method of narrowband interference(NBI)suppression to improve the anti-jamming capacity.The main work and contributions are summarized as follows.1.Aiming at the problem of the signal damage caused by the transform domain NBI algorithms,the RobustICA algorithm is applied to separate the DSSS signal from the mixed signal.In order to improve the robustness to the isolated points,this algorithm combines the exact line search method with the kurtosis.Simulation results show that compared with the negentropy-based FastICA NBI suppression method,it has the better performance for the multi-tone NBI by decreasing the probability of falling into the saddle point or the local point,and increases the reliability of the NBI method based on the blind source separation.2.Aiming at the problem of the low convergence speed caused by the highly correlated received signal,and the high computational complexity caused by the P input vectors,a decorrelating affine projection algorithm with variable order is applied to decrease the convergence speed and the computational complexity.The input signal was decorrelated,and then the step size was optimized using the received signal's orthogonal vector.Furthermore,a new updating strategy for projection order was proposed based on the characteristic of received signal.Simulation results showed that,compared with variable step-size affine projection algorithm,the algorithm proposed had faster convergence rate,lower complexity,and lower normalized mean square error.This new algorithm has 3dB ber improvement for the suppression of the BPSK narrowband interference,compared with the variable step-size affine projection algorithm.3.Aiming at the problem of the larger signal damage caused by taking the optimal frequency shift for the highest power interference without considering the interference at other frequency,a new algorithm based on the optimal frequency shift for multi-tone interference suppression is applied to decrease the signal damage.The algorithm combines the optimum frequency shift with the undecimated wavelet packet transform(UWPT)to locate the energy of each interference component in as little sub-band as possible.In addition,the adaptive algorithm is used to reduce the harm to the signal caused by eliminating the disturbed sub-band.Simulation results show that the proposed algorithm has about 2dB ber improvement than the undecimated wavelet packet transform with frequency shift(SUWPT)algorithm in the suppression of the multi-tone interference.