Study On The Estimation Algorithm Of Parameters And Spread Spectrum Sequence Of DSSS

Direct sequence spread spectrum(DSSS)communication system has been widely used in civilian and military communication system because of the advantages with working in low SNR environment,low probability of intercepting,good confidentiality,strong anti-interference and anti-fading ability.With the rapid development of electronic and network information warfare today,direct sequence spread spectrum communication has become a hot research topic in communication confrontation.How to solve the required information from the signal with a better estimation algorithm and achieve the purpose of communication reconnaissance is a major issue in the research of direct sequence spread spectrum communication confrontation field.Therefore,this thesis studies the estimation problem of the parameters and the spread spectrum code sequence from the received DSSS signals in non-cooperative communication.The performance of the estimation algorithm is verified by simulations.The main parameters of the DSSS signal are carrier frequency,chip rate,spread spectrum code period,spread spectrum code synchronization point and spread spectrum code sequence.For the carrier frequency estimation,the square doubling frequency method and the correlation accumulative technique are studied,and the algorithm derivation and experimental simulation of the square doubling frequency method are carried out.For the estimation of chip rate,the delay-and-multiply and Haar wavelet transform are used to estimate the chip rate of DSSS signal at low SNR.For the spread spectrum code period estimation,the classical average auto-correlation second moment method and the improved delay-and-multiply second power spectrum method are studied,and the performance of the two algorithms is compared.Meanwhile,the performance of two algorithms is compared by simulations for the periodic long code direct spread signal.For the spread spectrum code sequence estimation,the classical eigenvalue decomposition algorithm is studied,and the simulation method is used to estimate the effect,and the advantages and disadvantages of the algorithm are analyzed.A spread spectrum sequence estimation based on an adaptive iterative method for fast orthogonal projection approximation subspace tracking is proposed in the non-synchronous case,the wide window method and the improved sliding window technique are given to overcome the problem of the phase uncertainty of the spread spectrum code sequence estimation.Based on this,combining the spectral norm and fast constrained projection approximation subspace tracking algorithm of the spread spectrum sequence estimation algorithm are proposed for periodic long code direct spread signal.Simulation results show that the DSSS signal synchronization algorithm of spectrum norm algorithm is used to estimate the synchronization point information,and then subspace tracking algorithm can be realized code sequence estimation under the condition of low SNR in lower complexity and smaller computation.Finally,we successfully estimate the information of parameters and code sequence,verify the correctness and the validity of the algorithms by parameter estimation and spread spectrum sequence estimation of actual DSSS signal sample data.All appropriate estimation algorithms are applied to the signal processing off-line test platform constructed by Visual C++6.0,which provides a theoretical and practical basis for hardware implementation of receiving DSSS signal.