Blind Equalizer Design And Algorithm Study Based On Fractionally Spaced

In underwater acoustic digital communication, the severe inter-symbol interference, caused by multi-path effects and channel distortion of sound propagation, degrades the reliability and decreases the rate of the propagation, is the chief obstacle of high speed underwater sound correspondence. The conventional equalizer resort to a training sequence in order to overcome inter-symbol interference. As a result of channel's time-variable characteristic, needs to transmit the training sequence to track channel's change frequently, such massive training sequence will take the very great band width. However, The blind equalize technology does not need to transmit the training sequence to be possible to track the channel change, and enhances the data effectively the transmission speed and the reliability. Along with the development modernized from underwater sound correspondence to the high speed intelligence transmission, and it has the important meaning to analysis and research the theory and the algorithm of blind equalize in view of the underwater sound channel.This article in view of underwater sound channel characteristic, has conducted the thorough research to the algorithm of constant modulus and the structure of fractionally spaced equalizer, and simulation in underwater sound channel. The main contribution of this dissertation are summarized as follows:1 Introduced the characteristic of underwater sound channel and the structure of blind equalizer, review the principle of work of fractionally spaced equalizer, studied the constant modulus algorithm based on T/4 fractionally spaced equalizer. The result of deep spectrum underwater sound channel's computer simulation has proven the good performance of convergence rate and remainder mean square error this algorithm.2 The blind equalization algorithm based on T/4 fractionally spaced decision feedback equalizer is proposed. The proposed algorithm can overcome the shortcoming that in the case of linear equalizer, when the zero spot of channel transmission function in the unit circle, or, the actual channel's transmission function has the public zero spot, the constant modulus algorithm cannot restrain.3 To overcome the shortcoming of CMA slow convergence rate, the algorithm of decorrelation and momentum is applied to Fractionally spaced decision feedback blind equalizer.Fractionally spaced decision feedback equalizer based on decorrelation algorithm is presented. The computation of proposed algorithm is simple and the convergence rate is quick.T/4 fractionally spaced momentum blind equalizer with decision feedback structure is proposed. The performance of momentum algorithm can speed up the convergence rate in the case of small mean square error curve, and the good equalize performance of fractionally spaced equalizer.The efficiency of the proposed equalizer is proved by computer simulation in underwater acoustic channels.4 The cascade blind equalizer is designed by connection T/2 fractionally spaced equalizer with baud spaced equalizer. The structure of proposed equalizer has good performance. The revision algorithm adjust the fractionally spaced equalizer taps to overcome the phase rotation, and the baud spaced taps is adjusted by CMA. The proposed algorithm has overcome the phase rotation, speed up the convergence rate and reduce the surplus mean square error, and enhance the complex underwater sound performance of complex underwater sound channel.