Rake Receiver Technology In Underwater Acoustic Communication

Underwater acoustic communications(UWA) are made difficult by the combined effect of multipath propagation and high temporal and spatial variability of the channel conditions. The fading which was caused by multipath propagation was one of the main factors influencing the performance of underwater acoustic communication systems. The purpose of this thesis is not only to overcome multipath interference by spread spectrum but also to improve the performance of the system by employing RAKE receiver to recombine some multipath signals.Firstly, some useful experience about designing underwater acoustic communication systems and the properties of underwater acoustic channels are introduced . Then, introducing something about spread spectrum technique .and deciding to select direct-sequence spread spectrum(DS) in underwater acoustic communications by comparing DS to FH according to the properties of underwater acoustic channels. After that, discussing something about RAKE receiver, simulating the path-search algorithms, synchronization circuits and RAKE receiver in low speed underwater acoustic communications and analyzing some major factors influencing the performance of systems. Finally, after some experiments about RAKE receiver are performed in space channels, some problems existing in the process of experiments are mentioned ,and then, the simulation of FPGA about the path-searching circuit is finished.