| Spread spectrum signal is widely used in underwater acoustic communication because of its low peak-to-average ratio and difficult interception.The interception and identification of spread spectrum signal in underwater acoustic communication under non cooperative condition is a hot and difficult point in underwater acoustic signal processing.With the development of chaotic spread spectrum technology,it is more difficult to intercept and process the chaotic spread spectrum signal in underwater acoustic communication.Based on the characteristics of underwater acoustic communication,the identification and parameter estimation of chaotic spread spectrum signal in non-cooperative underwater acoustic communication are studied in this paper.The specific work is as follows:(1)The identification method of underwater acoustic communication chaotic spread spectrum signals based on maximum Lyapunov exponent is proposed.The C-C method is used to calculate the phase space reconstruction parameters,and the maximum Lyapunov exponent of the signal is calculated in the reconstructed phase space.The calculation results can reflect the chaotic characteristics of the signal.Aiming at the identification problem of chaotic spread spectrum signal,the identifiability of chaotic sequence,chaotic spread spectrum signal,noise and other underwater acoustic communication signals is analyzed,and the maximum Lyapunov exponent is used as the identification feature to identify the chaotic spread spectrum signals.The simulation results show that the proposed chaotic spread spectrum signal identification method is feasible.(2)Aiming at the parameter estimation of underwater acoustic communication chaotic spread spectrum signals,the corresponding parameters to be estimated are analyzed according to the different modulation modes of the signal.For chaotic direct sequence spread spectrum signals,the carrier frequency,PN code period and chip width of the signals are estimated by using square frequency doubling method,autocorrelation method and cyclic spectrum method,and improved autocorrelation method based on signal square preprocessing is proposed to estimate the PN code period of chaotic direct sequence spread spectrum signals spread by real valued chaotic sequences.For chaotic frequency hopping signal,a parameter estimation method based on time-frequency ridge feature is proposed.According to the extracted time-frequency feature,the parameters such as frequency hopping period and center frequency are estimated.Finally,the simulation results verify the effectiveness of the proposed method.(3)The algorithm process of identification and estimation of underwater acoustic communication chaotic spread spectrum signals is designed and tested.Finally,the applicability of this method is verified by the analysis of measured data. |
