Research On Joint Frequency Domain Equalization And Decoding For Rateless Underwater Acoustic Communication

With the progress of human society,the attention of all walks of life is gradually attracted by how to fully develop and utilize marine resources,researchers around the world are paying more and more attention to underwater communication technology.However,due to the serious multipath propagation phenomenon and long transmission delay of the underwater acoustic channel,the effectiveness and the efficiency of information transmission are severely limited.For these problems,the following parts of works are included:Firstly,the inherent physical characteristics of the underwater acoustic channel are analyzed,the BELLHOP underwater acoustic channel model is used to simulate the actual underwater acoustic channel for algorithm research.Based on the underwater acoustic channel,the fundamental for the main research algorithms of this paper are introduced and analyzed.The principle of coding and decoding of LT codes as a rateless codes is analyzed.The fundamental of blind equalization and the algorithm commonly used such as Constant Modulus Algorithm(CMA)and Multi-Modulus Algorithm(MMA)algorithm are also analyzed,and the reason for choosing MMA algorithm is given in this paper.Secondly,to address to the problem that the multipath fading of underwater acoustic channel creates inter-symbol interference,a blind equalization algorithm without training sequence is adopted in this paper,which saves channel bandwidth because it does not need to send training sequences.On the other hand,the blind time domain equalizer has a high computational complexity in the underwater acoustic channel,so fast frequency domain blind equalization is adopted for better performance of equalization.In addition,based on the frequency domain blind equalization,the fast blind frequency domain equalization based on the decision feedback structure is studied and which can optimize performance.Due to the traditional fixed tap length equalization cannot predict the optimal tap length according to the current hydroacoustic environment,the fast blind frequencydomain equalization based on the decision feedback structure using the tap length update algorithm is adopted to realize the variable feedforward tap length.Finally,channel coding is often utilized to ensure reliable transmission of links in the underwater acoustic communication system.Traditional source coding has a fixed code rate,such as convolutional codes,so feedback retransmission mechanism is regularly applied to implement error control.Poor channel conditions cause a considerable amount of retransmission requests,which leads to a lower communication rate.For this problem,the joint variable tap fast blind frequency domain equalization and rateless decoding algorithm is studied,which not only utilizes the coding flexibility of rateless code,but also improves transmission reliability of communication in underwater acoustic communication by combining fast blind frequency domain equalization and decoding.