Research On Transmission Characteristics Of Time-varying Channel Under Sound Source Motion

The characteristics of underwater acoustic channel are more complex than those of terrestrial wireless channel,such as severe Doppler effect,multipath effect and time-varying characteristics,which seriously affect the accuracy and efficiency of underwater acoustic channel simulation and estimation.In order to solve the above problems,based on the physical characteristics of underwater acoustic channel,this paper deeply studies the transmission characteristics of time-varying channel from two aspects of underwater acoustic channel modeling and parameter estimation.The research work is as follows:(1)The time-invariant underwater acoustic channel is simulated by ray acoustics and BELLHOP modeling tools.Combined with the analysis of underwater Doppler effect,the multi-scale and multi-delay characteristics of the time-varying channel are described.On this basis,the time-varying underwater acoustic channel under the condition of calm sea surface and sinusoidal undulating sea surface is simulated by Vir TEX algorithm,and the transmission characteristics of the time-varying channel are analyzed by the transmitted signal and the received signal transmitted through the channel.(2)For underwater acoustic channel,the traditional time delay parameter estimation method based on copy correlator is studied.The time delay resolution is limited by the bandwidth of the transmitted signal,so it is difficult to meet the high demand of channel delay estimation.In order to obtain higher delay resolution,the RL deconvolution algorithm and the hybrid algorithm of MUSIC spectrum estimation and least square estimation are studied.Simulation results show that RL deconvolution algorithm and hybrid algorithm have strong sidelobe suppression ability,and the parameter estimation accuracy of hybrid algorithm is better than that of copy correlator and RL deconvolution algorithm.(3)Under the condition of multi-scale and multi-delay channel,the parameter estimation performance of copy correlator algorithm,RL deconvolution algorithm and the hybrid algorithm of MUSIC spectrum estimation and least square estimation are verified.The simulation results show that the time delay and the scale factor are coupled and influence each other,and the error caused by the scale factor will be introduced in the time delay estimation.To solve the above problems,the joint estimation methods of scale factor and time delay based on broadband correlation processing and orthogonal matching pursuit are studied.The simulation results show that the orthogonal matching pursuit algorithm has high parameter estimation accuracy and stable performance.(4)According to the characteristics of CW signal,HFM signal and LFM signal,the estimation methods of scale factor are studied,that is,the joint estimation method based on FFT frequency measurement and ambiguity function,the estimation method based on superimposed HFM signal and the best order search method.The simulation results show that the optimal order search method has the advantages of high precision,flexibility and practicability.On this basis,a channel parameter estimation algorithm based on fractional Fourier transform is studied.In this method,the multi-component LFM signals are separated one by one according to the energy in an iterative way,and a sub-iterative process of correcting the optimal transform order is added in the iterative process.The simulation results show that this method can achieve good results in estimating the parameters of the main path and tracking the time-varying characteristics of the channel.