Blind Equalization Algorithm In Underwater Acoustic Communication Research

Underwater acoustic (UWA) channel which is important in UWA communication is full of various complicated factors. It results message distortion easily, so it needs an effective technology which is usually called equalization to compensate channel distortion and reduce even eliminate intersymbol interference(ISI). Traditional adaptive equalization technology needs to transmit the same training sequence repeatedly and periodically before sending actual data, which wastes bandwidth and reduces the communication efficiency. Therefore, a new equalization algorithm is needed urgently to overcome the shortcomings.This paper studies a new blind equalization algorithm, which can send actual data directly without training sequence and equalizes channel by using the sending data. It can effectively reduce the use of bandwidth and improve the efficiency of the communication. The main research content in this paper is:1.The simulation of the multipath UWA channel. The multipath channel is the most general and important channel in UWA communication. Comparing with the other channels, it will result serious ISI and increase the bit error rate (BER). So, at first, it studies the principle of the multipath channel, then analyses the influence of data when in the different depth and distance by simulation, which will help for the further research.2.The realization of Constant Modulus Algorithm (CMA). This paper studies the CMA and analyses the influence of different Signal to Noise Ratio (SNR) and orders of equalizer on algorithm performance by using CMA, then analyses an improved algorithm which can solve the phase deflection called Real part and Imaginary part separated CMA(RICMA). The validity of the algorithm is proved by simulation results.3.The realization of CMA based on different error functions. According to error function of CMA without symmetry, it studies two improved algorithms based on different error functions——Logarithm Error function CMA (LECMA) and Hyperbolic Tangent Error function CMA (HTECMA). The feasibility of these algorithms on signal equalization is proved by simulation results.4.The realization of CMA based on fractionally space equalizer (FSE). According to the low channel utilization of CMA, it studies a kind of blind equalization algorithm based on T/4FSE, which can obtain more useful information to realize better equalization. The validity of the algorithm is also proved by simulation results.5.The realization of CMA based on different criterions. According to the slow convergence rate, it analyses an improved algorithm which is based on two criterions. The validity of the algorithm is also proved by simulation results.In this paper, it proves the feasibility of these algorithms by using two diverse simulations. And the advantages and disadvantages of these algorithms are compared. Meanwhile, it also analyses the multipath channel and determines the channel for the simulation experiment.