| Due to the acoustic absorption effect of seawater,the bandwidth of underwater acoustic communication is limited and the communication rate is low.In recent years,application scenarios such as underwater voice and video have increasingly high requirements for communication speed.Therefore,how to improve the spectrum utilization rate under the premise of limited bandwidth resources of underwater acoustic channel transmission is particularly important.In order to solve this problem,the paper introduces the Fast-ThanNyquist(FTN)transmission technology in the conventional Nyquist system.Under the condition of a pulse-forming filter with the same bandwidth as the Nyquist system,FTN technology improves the transmission rate by compressing the transmission interval of the code element signal,thereby improving the spectrum utilization.This also led to the introduction of Inter-Symbol Interference(ISI)on the transmitter side of the FTN system.At the same time,the underwater acoustic channel has a long multipath extension,which further aggravates the ISI at the receiving end.In this paper,different equalization algorithms are used to process and study the ISI problem at the receiving end of the underwater acoustic FTN system,and the main work is as follows.Firstly,the basic theory of FTN signal is introduced,and it is found that when the acceleration factor decreases to a certain critical value,that is,the Mazo boundary,the Euclidean distance of the signal remains unchanged.Then,aiming at the ISI problem introduced by FTN signals,a baseband time-domain compensation method is studied.Secondly,aiming at the problem of further aggravation of ISI at the receiving point of FTN signal after passing through the channel,the equivalent model of FTN communication system is derived,and non-iterative Zero Coming(ZF)equalization,Mininum Mean Squared Error(MMSE)equilibrium,Decision Feedback Equalization are introduced.DFE)and the principle of the Turbo iterative equalization algorithm based on the MMSE criterion;Based on the FTN QPSK system,the above equalization technology is used to simulate communication under multi-channel channels,and the scope of application of different methods is obtained.Then,when the acceleration factor is too small for the FTN system,the non-iterative equalization algorithm and the Turbo iterative algorithm of MMSE perform insufficiently.In this paper,the interference cancellation module is introduced on the basis of the Turbo iterative equalization of DFE structure,and a decision feedback Turbo equalization technology based on interference cancellation is proposed.In this method,the soft information value or hard decision value output by the decoder is fed back to the equalizer after the estimated channel for interference cancellation,and the DFE iterative equalization(SIC-DFE-Turbo)based on soft interference cancellation(SIC)and hard interference cancellation based on Hard interference cancellation are obtained,respectively.HIC DFE iterative equalization(HIC-DFE-Turbo);The output value of the offset feed-forward filter and the feedback value of the decision output are weighted and superimposed as the output of the Soft input soft output(SISO)equalizer to improve the iterative equalization performance of the traditional DFE structure.The channel estimation algorithm based on orthogonal matching tracking is adopted.Finally,the FTN transmission system with different acceleration factors is simulated under the Proakis channel and the hydroacoustic channel measured in Weihai,and the convergence of the method is analyzed by the Extrinsic Information Transfer Chart(EXIT)in the iterative process,and the bit error rate of communication is analyzed.Finally,a set of underwater acoustic FTN image transmission scheme is designed,and FTN transmission experiments with different acceleration factors are carried out in the channel pool,and the experimental results verify that the proposed algorithm has the reliability and feasibility of underwater acoustic communication transmission... |
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