Research On Iterative Sparse Underwater Acoustic Channel Estimation And Equalization Technology

The typical underwater acoustic channels usually show sparse characteristics.The channel estimation method based on least square(LS)technique has the problem of noise enhancement under sparse channel conditions,and it does not make full use of the sparse characteristics of underwater acoustic channels,the channel estimation performance is poor.In addition,the multipath spread of underwater acoustic channel is serious,which leads to extremely serious frequency selective fading.The sparse channel estimation method based on compressed sensing can accurately reconstruct the signal,and the Turbo equalization technique based on modern encoding technology can achieve iterative equalization and decoding.Therefore,compressed sensing theory is applied to underwater acoustic channel estimation,and iterative channel estimation and equalization techniques are studied.Firstly,the basic theory of compressed sensing is introduced,and the sparse underwater acoustic channel estimation method based on orthogonal matching pursuit(OMP)and multipath matching pursuit(MMP)algorithm is studied.The dichotomous coordinate descenting(DCD)iterative technique is applied to OMP and MMP algorithms.The problem of large computation and numerical instability caused by matrix inversion in OMP and MMP sparse channel estimation algorithms is solved.Cross validation(CV)statistical technique is applied to OMP-DCD and MMP-DCD algorithms.The greedy iterative algorithm does not need priori knowledge such as sparsity and noise level,so the estimation accuracy of the algorithm is improved.OMP-DCD-CV and MMP-DCD-CV sparse channel estimation algorithms are proposed.In view of the serious deterioration of the performance of the band limited underwater acoustic communication system in the seriously disturbed underwater acoustic environment.Transformation domain communication system(TDCS)is introduced into the field of underwater acoustic communication.TDCS based on two sparse channel estimation algorithms is proposed to improve the spectral efficiency and robustness of underwater acoustic communication system under narrowband interference.Then,the research of iterative channel estimation and equalization under the condition of sparse channel is carried out.This paper reviews the basic principle of Turbo codes,including the structure of encoder,encoding principle and encoding grid map.Based on the idea of iterative decoding based on soft-in and soft-out,the paper studies the maximum a posteriori(MAP)and its simplified form of Log-MAP decoding algorithm.Finally,the basic idea and principle of Turbo equalization are introduced.The soft-in and soft-out Turbo equalization based on MMSE(Minimum Mean Square Error)is introduced and the research on underwater single carrier iterative sparse channel estimation and equalization.Finally,the simulation analysis and single carrier experimental data processing are carried out.In the part of numerical simulation,the reconstruction accuracy of channel estimation algorithm based on compressed sensing is simulated and analyzed,and the simulation of underwater acoustic single carrier iterative sparse channel estimation and equalization system is carried out.The underwater acoustic TDCS based on MMP-DCD-CV sparse channel estimation algorithm is simulated and analyzed.In the part of single carrier experimental data processing,the performance of various algorithms is verified and simulated by processing Songhua Lake test data.