Underwater Acoustic Spread Spectrum Communication System Simulation Research

Time-varying multipath is a main obstacle to underwater acoustic communications and spread spectrum is one of the techniques to improve the link performance in hostile underwater acoustic channels. The purpose of this thesis is to employ spread spectrum to overcome multipath. The properties of underwater acoustic channels and the effects of time-varying multipath propagation upon transmitted signals are analyzed in the first part. In the second part, we discuss the fundamental questions of spread spectrum and decide to select direct sequence spread spectrum(DSSS) in underwater acoustic communications. In the third part, we discuss the synchronization of spread spectrum signals. In the last part, we design the systems, including low and high speed underwater acoustic spread spectrum systems, and simulate them with System View. The results indicate that spread spectrum can overcome multipath very well in low rate systems but not so well in high speed systems because of multiple access interference(MAI) caused by multipath.