A Research On Multi-Domain Interference Suppression Technique In DSSS System

The spread spectrum communication system is widely used due to its strong anti-interference ability and low probability of interception and so on.But the modern communication environment is becoming more and more complex.Especially in the military aspect,the electronic warfare has become one of the important ways of modern warfare.Therefore,it is introduced the spread spectrum system interference suppression techniques from frequency domain,space domain and space-time domain in the thesis.Its main contents include:1.The differences between the time domain,frequency domain,space domain and the space-time interference suppression is introduced;the principle of direct sequence spread spectrum(DSSS)signal is summarized;the present often existing jamming(single tone interference,narrowband and wideband interference)is modeled.2.The frequency domain interference suppression technology is explored,which is mainly aimed at the single tone and narrowband interference.The frequency domain algorithm based on the double threshold is analyzed.Aiming at the higher complexity of the algorithm,the algorithm based on the frequency domain difference is adopted.To solve the problem of spectrum leakage,the overlapping windowing and frequency domain difference algorithm are combined to alleviate the spectrum leakage and also reduce the signal distortion.The simulation results show that the bit error rate of frequency domain difference algorithm based on overlapping windowing is lower than that of the double threshold algorithm.3.The spatial domain interference suppression technology is explored,which is mainly aimed at the single tone,narrowband and wideband interference with the different directions from the useful signals.The array receiving model of specific spread spectrum signal is constructed.On the basis of this signal model,the several classical weight optimization criteria is compared;the Minimum Variance Distortion-less Response(MVDR)algorithm and the Power Inversion(PI)algorithm is simulated.And the results have shown that the PI algorithm does not need the prior knowledge,but its output Signal to Interference plus Noise Ratio(SINR)is lower than that of the MVDR algorithm.On the basis of the PI algorithm,the spatial domain anti-jamming algorithm based on the orthogonal subspace is simulated and analyzed.And it is concluded that the output SINR based on the orthogonal subspace algorithm is between the PI algorithm and the MVDR algorithm.On the basis of the above algorithm,the interference suppression technology of wideband array signal is studied when the bandwidth of spread spectrum signal is wider.4.The technology of space-time interference suppression is explored,which is mainly aimed at the single tone,narrowband interference with the same directions as the useful signals and the wideband interference with the different directions from the useful signals.The classical space-time interference suppression technique based on the LCMV is simulated.When the interference is in the same direction as the useful signal,the output SINR of the algorithm is higher than that of the pure spatial domain algorithm.However,it needs to invert the sampling matrix directly,when the number of the array elements or time domain taps is larger,the algorithm requires a large amount of computation.Therefore,the space time algorithm based on the LMS is studied by combining the LCMV and LMS.In this way,the original computational complexity is reduced.The convergence step of LMS algorithm is analyzed in detail,and a spatial time LMS algorithm with variable step is determined.The algorithm not only improves the convergence rate,but also takes the steady-state performance into account.The simulation results show that the output SINR of LCMV algorithm is higher than that of LMS with variable step when the estimation error of arrival angle of useful signals is smaller.Conversely,the output SINR of variable step LMS is higher.