Research On Adaptive Equalization In Underwater Acoustic Communication System

Underwater acoustic communications are made difficult by the effect of multipath propagation. The fading which was caused by multipath propagation was one of the main factors influencing the performance of underwater acoustic communication systems. Adaptive equalization techniques have been developed over last three decades which can overcome Inter-Symbol Interference caused by multipath propagation.In this paper, two basic algorithms of adaptive filter- LMS (Least Mean Squares) and RLS (Recursive Least Squares) algorithm-are analyzed. Then, in order to make compromise between LMS algorithm with fixed step contradicts with the demand of parameter μ in aspect of the rate of convergence and track speed of real time system and the precision of convergence, two new LMS algorithms with variable step are introduced. Because of some intrinsic defects of RLS algorithm, some improved RLS algorithms such as SPRLS, MRLS algorithm are analysed. RLS algorithms with a adaptive forgetting factor is used to update the tap-coefficient vector of the DFE in order to minimize the squared equalization error due to input noise and due to channel dynamics. At last, this thesis presents the LSL algorthm which is the more sophisticated processing algothm capable of operating in uncertain, time-varying environments because of its latticelike structure. Computer simulaiton results demonstrate that better transmission performance can be achieved by adaptive equalization technology.