Research On Countermeasure Method For Underwater Acoustic DSSS Communication Signal

Direct sequence spread spectrum communication is widely used in long-range underwater acoustic communication,concealed underwater acoustic communication,high quality underwater acoustic communication and code division multiple access underwater acoustic communication due to its strong anti-interference ability,high concealment,strong multi access ability and high time resolution.The traditional methods of underwater acoustic communication interference include blocking interference,single tone interference or multi-voice interference.Although the prior knowledge of communication signal parameters is not required,these methods have some disadvantages such as low interference efficiency,power waste or exposure.This paper focuses on the research of the Countermeasures for underwater acoustic direct expansion communication signals.The basic is the effective parameter estimation of the underwater acoustic DS communication signals.The ultimate purpose is to effectively interfere with the DS communication.The main contents of this paper are as follows: one is the parameter estimation method of the underwater sound direct expansion signal;the other is the blind estimation method of PN sequence;the third is the conventional interference of underwater acoustic direct expansion communication and the analysis of the best interference effect.In this paper,three basic parameters estimation methods of the uncooperative underwater acoustic direct expansion communication signal are studied.The carrier frequency estimation of DSSS signals is carried out by square frequency multiplication and square frequency correlation Cumulation method respectively.The square frequency multiplication correlation Cumulation method has lower signal-to-noise ratio tolerance;the delay phase multiplication and wavelet transform are used to estimate PN code rate of DS signals.Wavelet transform algorithm eliminates the constraints of prior knowledge required for delay phase multiplication;time domain autocorrelation method and secondary power generation method are used The spectrum method is used to estimate PN code period,which has better performance in multipath channel.Based on the correct estimation of the above parameters,this paper studies the blind estimation algorithm of PN sequence of underwater acoustic direct expansion signal.Firstly,the basic feature analysis method is studied,and the wide window sampling method is introduced to improve the inverse phase of PN sequence in the original method.Aiming at the problem of large computation of feature analysis,PN sequence estimation based on Hebbian learning criterion and PN sequence estimation based on subspace tracking method are introduced.The two methods have a small amount of calculation,but bring higher SNR tolerance.Finally,a PN sequence estimation method based on maximum likelihood function is proposed,and the performance of the method is improved compared with the previous two algorithms.The validity of the above algorithms is verified by simulation and sea test data.The final expression of communication confrontation is to implement communication interference.After the necessary parameter estimation of underwater acoustic direct expansion signal,this paper studies the interference effect of noise interference,audio interference and related interference.Finally,the underwater acoustic direct expansion communication reconnaissance and counter pool test are carried out.The experimental results show that the correlation interference is the most efficient one of the three methods.