| To achieve reliable underwater acoustic communication in complex time-varyingfrequency-varying-space channels,the modulation scheme for underwater acoustic communication needs to be further explored.Orthogonal Time Frequency Space(OTFS)modulation system has better performance gain than Orthogonal Frequency Division Multiplexing(OFDM)modulation system in terrestrial high-speed communication,so it has been introduced into underwater acoustic communication in recent years.communication in recent years.In this paper,the OTFS system model under underwater acoustic channel is studied and analyzed,and the channel equalization and estimation techniques applicable to the underwater acoustic OTFS system are investigated,and the main research contents are as follows:Firstly,the characteristics of the underwater acoustic channel are analyzed,and the underwater acoustic channel model is established and analyzed.Then,the basic principle of OTFS is introduced,and the received signal model of underwater acoustic OTFS communication system is established,and consider the problem of Doppler estimation and compensation.Secondly,the channel equalization algorithm applicable to the underwater acoustic OTFS communication system is studied,which mainly includes linear equalization and nonlinear equalization.This paper analyzes the Zero forcing(ZF)equalization,Minimum Mean Squared Error(MMSE)equalization,and the classical Message Passion(MP)algorithm of nonlinear equalization algorithm,through simulation analysis,it can be concluded that the performance of MP equalization algorithm is better than the performance of two linear equalization algorithms.The channel estimation algorithm of the underwater acoustic OTFS system is studied again.Since the received data of the OTFS system is in the time-delay-Doppler domain,which is twodimensional,most of the channel estimation algorithms of the OTFS system are based on twodimensional,so the channel estimation algorithms studied in this paper are also carried out in two dimensions.The specific algorithms include the noise-threshold-based channel estimation algorithm and the two-dimensional OMP channel estimation algorithm,and the OMP schemes under different guide structures are analyzed and compared.According to the simulation analysis,the two-dimensional OMP channel estimation scheme outperforms the noisethreshold-based channel estimation scheme.The MSE performance of the algorithms for OMP channel estimation with two different guide structures is different at low SNRs,but the performance converges at high SNRs.And the two guide structures have different application ranges,where the embedded guide based OMP channel estimation is applicable to more cases and can perform channel estimation in real time.Finally,the performance of the channel estimation and equalization algorithms of the underwater acoustic OTFS system with different channels is analyzed and compared.The feasibility of the underwater acoustic OTFS communication system is verified in the underwater acoustic channel with Doppler factor.The simulation results are also verified in practical experiments. |
