The Research Of Equalizer In Underwater Acoustic Communications

With the undersea exploration and data transfer rate of underwater acousticcommunication demand increasing, the technology of underwater acoustic communicationhas been rapidly developed, and among that, the channel equalization technique is the criticalone. Base on different equalization algorithms and equalization structure, this paper detailedlyanalyzes the theory and derivation of the adaptive algorithm LMS(Least Mean Square error),DFE(Decision Feedback Equalization) and CMA(Constant Modulus Algorithm),andsimulates with the underwater acoustic channel. Then combined with shallow water acousticchannel characteristics, analyzes the features of the improvement algorithmVSS-LMS(Variable Step-Size LMS) and MCMA, and gets in the underwater acoustic channelequalization simulation to compare their improvements.This paper builds the simulation system with two parts: the channel modeling part andthe equalization algorithms part. The channel modeling is based on the ray theory, using theNewton-down to search all the eigenray and calculate their attenuation, and finally gets theimpulse response of the underwater acoustic system. We make this part with a MATLAB GUIprogram, which can set parameters conveniently in order to get different impulse response ofdifferent underwater environment providing for the equalization simulation. The equalizationalgorithms part simulates the LMS, DFE and CMA equalization algorithm in the underwaterchannel obtained with the first part and analysis the result. Then according to thecharacteristics of underwater acoustic channel, raises the advanced algorithm VSS-LMS,MVSS-LMS and MCMA. The simulation result shows that MVSS-LMS performed better andis more suitable to the time variation of the channel, while the MCMA algorithm equalizebetter with its phase correction function.