Research On Blind Despread Spectrum For DS-SS Signal Based On Fast-ICA

Direct Sequence Spread Spectrum (DS-SS) signal has the advantages of multi-path, anti-jamming, low probability of intercept, multiple access multiplexing, which is widely used in military and civilian communication fields. For non-cooperative communication situations such as reconnaissance, monitoring of radio spectrum and tracking of illegal radio communication, intercepting signal and despreading signal for restoring information transmission in the condition of unknown spread spectrum sequence is necessary, so carrying out DS-SS signal blind despreading research in communication countermeasure fields has important significance.In this thesis, aiming at the problem of estimation of the spread spectrum code sequence of long code DS-SS signal in the non-cooperative case, Independent Component Analysis (ICA) method is adopted to research, the main work is as follows:First of all, the research status and development trend of blinding estimation to DS-SS signal are introduced, and the signal model of DS-CDMA system and DS-SS communication system is analysed.The basic principle of the ICA is discussed.Secondly, on the basis of the analysis of CDMA and ICA model, some traditional blind estimation algorithms of spreading spectrum sequence are studied. Aiming at the present situation that the traditional algorithms can be only applied into blind estimation of short-code DS-SS signal. A signal model of the new cycle long code DS-SS, virtual multi-user model, is proposed, which can make the long code spread spectrum signal equale to short code signal, and then the Fast-ICA algorithm can be applied to this model. Simulation results show that, the model proposed in this thesis can be applied in blind estimation of long code signal, and the estimation performance is satisfied.Thirdly, on the basis of virtual multi-user mode, the long code signal is estimated piecewise and the preprocessing of traditional Fast-ICA algorithm is improved, then the Fast-ICA algorithm without whitening is proposed. The improved algorithm is applied to estimate long code DS-SS signal, simulation results show that the convergence speed of this method is faster, which can estimate the spread spectrum sequence correctly at the same time.Finally, the research of this thesis is summarized, and the future research is prospected.