Research On Underwater Acoustic Spread Spectrum Communication Technology Based On Space-Time Processing

In recent years,people pay more and more attention to the ocean,and continue to strengthen the research of the ocean.The underwater acoustic communication is an important method to explore the ocean.It is also an effective way of information transmission in the ocean.However,due to the serious interference in the marine environment and the extremely complex channel,the underwater acoustic communication is difficult.This paper is devoted to the research of an underwater acoustic communication method to realize the effective and reliable transmission of underwater information.The spread spectrum communication technology has the good anti-jamming performance and can ensure the reliable communication in complex environment,so it is often used in underwater acoustic communications.This paper studies the underwater acoustic spread spectrum communication technology,and starts from the principle of the spread spectrum communication.It introduces the basic theory of the spread spectrum communication and common spread spectrum sequences.Besides,this paper analyzes the direct sequence spread spectrum communication system.Because of the low efficiency of the direct sequence spread spectrum communication,this paper introduces three improved spread spectrum methods to improve the communication rate.The performance advantage of the underwater acoustic spread spectrum communication system is verified by the simulation.Furthermore,the influence of the spread spectrum modulation mode,the spread spectrum sequence and other factors on the performance of the underwater acoustic spread spectrum communication system is analyzed.The typical multipath structure of the underwater acoustic channel causes delay spread and angle spread of the received signals.In the underwater acoustic communication system,the signals emitted by the source will arrive at the receiver along different paths,and these multipath signals have different propagation delay and direction of arrival.Therefore,the received signals can be regarded as the superposition of several space-time clusters.Considering the use of a linear array to receive signals at the receiver,this paper studies the DOA estimation techniques suitable for different signals and the beamforming methods in different processing domains.Then,it analyzes the applicable conditions and the performance of each algorithm,and selects the appropriate algorithms to obtain the space-time cluster characteristics of the received signals.The focus of this paper is to study a kind of underwater acoustic spread spectrum communication system based on space-time processing,which uses a linear array to receive signals.And this paper introduces a space-time processor to extract and combine the space-time clusters of the received signal,so as to obtain both the space gain and the time gain.It can reduce the requirement of the input signal-to-noise ratio,and make the communication system remain robust in a relatively harsh underwater acoustic environment.In this paper,the proposed communication system is simulated.Compared with other underwater acoustic spread spectrum communication systems,the high reliability of this system is analyzed and verified.Finally,the performance of the underwater acoustic communication system under different modulation modes and different receiving modes is analyzed by the pool experiment.The results are consistent with the theory and the simulation,which verifies the feasibility of the underwater acoustic spread spectrum communication system based on space-time processing.