Research On Shallow Water Acoustic Communication Based On Direct Sequence Spread Spectrum Techniques

With the rapid development of ocean and information technology,the requirement of transmitting the data through the underwater acoustic channel is increasing greatly.The signal's fading which is caused by underwater especially shallow water acoustic channel multipath propagation is the main factors influencing the performance of underwater acoustic communication systems.Because of direct sequence spread spectrum(DSSS) techniques' ability of resisting multipath interference and multi-access,it is the key technique which is used to transmit data in underwater wireless acoustic communication networks.This thesis briefly introduced the development of domestic and abroad research on underwater acoustic communications and the research orientation on spread spectrum communication,and then the properties of shallow underwater acoustic channels and the effects of time-varying multipath propagation upon transmitted signals are analyzed.In the third part,we introduce the key technology of direct sequence spread spectrum communication.Channel parameters estimation is need in the design of RAKE receiver or equalizer of direct sequence spread spectrum communication system,so in the fourth part,we presents a novel method of underwater acoustic channel estimation which initially uses LMS algorithm to acquire channel parameters in convergence mode and then converts to SOLMS algorithm for channel tracking after convergence(in tracking mode),this new method combines the merits of the fast convergence rate of the LMS algorithm and the better tracking performance of SOLMS algorithm.According to shallow underwater acoustic channels' characteristics of long multipath spreads and rapid time variations and evidence fluctuations,an underwater acoustic communication system based on DS/DBPSK technique was present in this paper,this scheme adopts digital matched filtering,delay differential demodulation techniques and so on,and it doesn't need pseudo random codes synchronization and carrier wave extraction.At last,a DS/DBPSK underwater acoustic communication system based on a chip TMS320C6713 is set up combined with some peripheral circuits.And the experiment results gathered in the lake and in Xiamen port are given.