Research On Underwater Acoustic Communication System Based On Chirp Carrier Spread Spectrum Orthogonality

With the human demands for marine resources and marine space,underwater activities such as exploiting marine resources need the help of underwater acoustic communication,thus underwater acoustic communication has become a hot research now,It is necessary to build a highly robust underwater acoustic communication system.This paper mainly studies Chirp spread spectrum,Chirp spread spectrumtechnology doesn't require pseudo-random sequence for frequency expansion,because Chirp carrier itself is a broadband signal,in addition,Chirp signal also has good anti-multipath and anti-Doppler frequency shift performance,so Chirp spread spectrum technology is frequently used in underwater acoustic communication.In order to improve the communication rate,this paper proposes a M-ary spread scheme which combines cyclic shift keying based on Chirp carrier and modulation scheme based on frequency band division,selecting the frequency band through the M-ray frequency keying,adopting Chirp carrier cyclic shift keying module in each sub-band,using the cyclic shift characteristic of the Chirp carrier and the information is carried by the shift length of the carrier.In order to improve the systematic communication capacity to a greater extent,this paper also proposes two multi-user modulation schemes which are based on Chirp carrier cyclic shift keying,multiple signal superimposed together in the transmitter,then using point-to-point transmission to simulate multi-user communication,the scheme distinguishes the user by Chirp-rate and center frequency of Chirp carrier respectively.The system performance is verified in Gaussian white noise channel and multipath channel.For the sake of solving the problem of inconvenient and high cost of ocean experiment,this paper integrates the commonly used channel model into MATLAB GUI to form a channel simulator for system simulation.Besides,a time-frequency analysis method of broadband underwater acoustic signal is proposed to extract channel characteristics,this method emploies fractional Fourier transform to carry out signal decomposition,and GWT for time-frequency analysis of multi-component signal,the simulation results show that the proposed means can analyze the multipath and delay of the channel more clearly.In order to reduce Doppler interference in the channel,a Doppler estimation method which combines fractional Fourier transform and multi-correlator method is proposed,simulation results show that the proposed method is highly accurate.The main work of this paper is summarized as follows:? The widely used channel model,such as BELLHOP model,RayTracing model,VirTEX and the channel model obtained in the Wuyuanwan are integrated into the MATLAB GUI to form the channel simulator.? A time-frequency analysis method of broadband underwater acoustic signal is proposed,the method uses fractional Fourier transform to carry out signal decomposition and GWT for time-frequency analysis of multi-component signal.? The Doppler factor is estimated by using the fractional Fourier transform combined with the multi-correlator method.The channel estimation method based on fractional Fourier transform and matched filter is compared.? A M-ary spread scheme which combines cyclic shift keying based on Chirp carrier and modulation scheme based on frequency band division,and a cyclic shift multi-user modulation scheme based on Chirp carrier are proposed.