Based On Variable Structure Blind Equalization Algorithm

In the field of underwater acoustic communications, the inter-symbol interference caused by multi-path effects decrease the reliability and the rate of the propagation of underwater acoustic signals. To settle this problem, an effective way is adopting an equalizer at the receiver. But the traditional adaptive equalizers need periodically retrained, because the underwater acoustic channel is a stochastic time-varying channel. Although the traditional adaptive equalizer increases the reliability of the propagation, the rate of it is decreased. So they are not very applicable in the field of the propagation of high rate signals through an underwater acoustic channel. To overcome the defect of the adaptive equalizers, this thesis deal with the technique of the blind equalization that need not the training period. This dissertation systematically studies channel blind equalization techniques applied to underwater communications. The main contributions are as follows:The characteristics of underwater acoustic channels as well as their effects acting on the performance of communication systems are analyzed from the point of view of communications, and the modal of underwater acoustic Multipath channels based on ray theory is established. Meanwhile, both the principle and the algorithm evaluating criterion of underwater acoustic channel blind equalization are also discussed.This thesis investigates a few of blind equalization algorithms that are broadly used. These equalizers' structures and principles are introduced in detail. In addition, in order to speed up the convergence process, a modified approach named variable step multi-modulus algorithm for eliminate the channel resulting multi-path effect is proposed, it can adjust step automatically. And the computer simulation results confirm the effectiveness of the algorithm.Using a fractionally spaced decision feedback equalizer, a nonlinear constant modulus blind equalization algorithm is proposed for equalization processing in multi-path acoustic channels. And this algorithm generalizes Volterra modal algorithm, which can effectively combat the widely existing ISI in underwater acoustic communications, and further suppress the serious inter-symbol...