Characteristics And Estimation Methods Of Underwater Acoustic Channel Under Random Fluctuation Sea Surface

The ocean belongs to a complex acoustic medium,which is characterized by the inhomogeneity of ocean boundary and interior of the sea.The inhomogeneity of sea surface results from the random fluctuation of sea waves.In complex marine environments,especially in shallow sea,the random fluctuations of sea waves can lead to the scattering and reflection of sound waves.The scattering and reflection of the sea surface will produce multi-path signals,which will interfere with each other at the receiving hydrophone.And then lead to energy attenuation and make the underwater acoustic channel appear different characteristics,thus affecting the quality of underwater acoustic communication system.Therefore,it's significant to study the influence of scattering and reflection of randomly fluctuation sea surface on the characteristics of underwater acoustic channel.In this paper,a one-dimension Gauss random fluctuation model is used to illustrate the relationship between the root mean square height and the correlation length and the fluctuation characteristics of rough surface.Considering that the fluctuation of sea surface wave is mainly affected by wind speed,the spectral function of sea surface is not suitable for Gauss distribution,so the wave spectrum-PM wave spectrum affected by wind speed variable is given.The spectral function is derived from the observational data of fully growing waves.Then the Monte Carlo method is used to establish a two-dimension sea surface model based on the PM wave spectrum,and the influence of wind speed on the height of the sea surface fluctuation is analyzed.Also,the one-dimension random fluctuation sea surfaces based on the PM wave spectrum under different wind directions is established,and the influence of wind speed on the root mean square height and correlation length of the sea surface is studied.The scattering and reflection effects of sound waves on the sea surface are important reasons for generating multipath signals and energy attenuation.Therefore,the scattering and reflection characteristics of random fluctuation sea surface are studied in this paper.First,the scattered sound field of the random fluctuation sea surface based on the PM wave spectrum is calculated using the integral equation method.Then the in-plane scattering characteristics are analyzed,and the scattering characteristics of the random fluctuation sea surface under different conditions,including the wind speed,the wind direction angle and the acoustic frequency,are studied.Considering the high frequency,the acoustic propagation model in the random fluctuation sea surface environment is established by using the ray model,which combines the fluctuation characteristics and the acoustic scattering characteristics of the random fluctuation sea surface.The transmission loss of sound wave and the impulse response of the channel are affected by the wind speed of the sea surface at different propagation distances.The results show that wave fluctuation will lead to the rapid attenuation of acoustic energy,and the magnitude of wind speed has a greater impact on the peak range of propagation loss.The larger the wind speed is,the worse the sea condition is.And the smaller the energy amplitude of the sound rays is,the less the number of arrival paths is.Underwater acoustic communication is one of the most important means to realize the underwater information exchange technology and information perception technology.There are many kinds of underwater acoustic communication systems,and all require high accuracy of channel estimation.For different underwater acoustic channel environment and different communication system,the methods of channel estimation are different.In this paper,the estimation method of underwater acoustic channel based on PM wave spectrum in random fluctuation sea surface is studied.The estimation algorithm includes LS algorithm,LMS algorithm,l₀-LMS algorithm,MP algorithm and OMP algorithm.By using LS algorithm,LMS algorithm,l₀-LMS algorithm,MP algorithm and OMP algorithm,the random fluctuation sea surface channels under different wind speeds are estimated.To compare the performance of different algorithm,the mean square error of the estimated channel under different SNR is calculated.