Research On Soft Decision Equalized Underwater Acoustic Communication Based On Approximate Message Passing

In underwater acoustic communication,although Orthogonal Frequency Division Multiplexing(OFDM)technology has high communication rate,it faces the following problems: Firstly,the common frequency domain equalization technology has low complexity,but does not consider the influence of noise,and the communication quality is not high.Secondly,although the Turbo equalization algorithm based on soft decision improves the communication quality,it has high complexity and is difficult to meet the needs of real-time applications.Based on this,the thesis combines the approximate message passing(AMP)algorithm with the Turbo equalization algorithm to reduce the complexity of the Turbo equalization algorithm.The specific research contents of this paper are as follows:Since this paper studies the channel equalization algorithm based on the known channel,the channel estimation results will affect the performance of the equalization algorithm.In order to reduce the performance degradation of the equalization algorithm caused by the channel estimation error,the Least Square(LS)algorithm,the Orthogonal Matching Pursuit(OMP)algorithm based on channel sparsity and the Sparse Bayesian Learning(SBL)algorithm are compared.The simulation and experimental results show that the SBL algorithm has the best channel estimation performance.Aiming at the problem that the traditional zero-forcing(ZF)equalization algorithm does not consider the influence of noise and has poor equalization performance,this paper studies the Turbo equalization technology based on MMSE criterion.Turbo equalization technology exchanges soft information between the equalizer and the decoder in an iterative manner,thereby achieving performance improvement and improving the reliability of the underwater acoustic communication system.In order to solve the problem of high computational complexity of Turbo equalization algorithm,this paper introduces AMP algorithm into it.The combination of generalized approximate message passing(GAMP)algorithm and vector approximate message passing(VAMP)algorithm with Turbo equalization algorithm is studied,which eliminates the matrix inversion process and reduces the complexity of Turbo equalization algorithm.At the same time,in order to ensure the convergence of the VAMP-Turbo equalization algorithm,a precoding scheme is introduced into the underwater acoustic communication system to meet the right orthogonal invariance condition required by the VAMP-Turbo equalization algorithm to achieve optimal performance.Finally,the paper verifies that the GAMP-Turbo equalization algorithm and the VAMPTurbo equalization algorithm can reduce the complexity of the Turbo equalization algorithm and improve the equalization performance through numerical simulation and field test.The proposed scheme can meet the requirements of underwater high-speed data transmission and reliability in applications such as underwater video transmission,unmanned platform and submarine data interaction.