Experimental study on variable structure adaptive equalizer for underwater communication system

The intersymbol interference caused by multi-path effects will make the reliability and the rate of the propagation of underwater acoustic signals very low. 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 deals with the technique of the blind equalization that need not the training period. This paper presents a new blind DFE which is based a modified CMA and has a dual mode structure. It does not need the periodic training and follows the changing channel very well through the timing structures. Simulation results show that the blind direct equalizer can deal with severe quickly time-varying channels such as underwater acoustic channels. The structure and principle of the equalizer is introduced in detail. The convergence properties of the equalizer applying in certain underwater acoustic channels is tested and analysed by computer simulations.