A Chaotic Spread Spectrum System For Underwater Acoustic Communication

Acoustic communication is the main way to exchange information underwater,which is of great significance to explore marine resources and to marine defense.The underwater acoustic channel is a time-space-frequency varying channel characterized by serious multipath effect,limited frequency band,complex environmental noises and significant Doppler frequency shift phenomenon,which makes underwater acoustic communication with low Bit Error Rate(BER)to be a challenging task.A novel chaotic spread spectrum acoustic communication method with lower BER is proposed in this thesis.A chaotic signal,generated by a hybrid dynamical system,is used as a spread spectrum sequence at the transmitter end.At the receiver end,a corresponding chaotic matched filter is used to decrease the effect of multiple propagation and noise.The proposed method does not require the complicated equalization and modulation-demodulation technologies that are necessary for conventional acoustic communication,which simplifies the structure of conventional direct sequence spread spectrum(DS/SS)system.Simulation results show that the proposed method has good anti-interference ability,resistance to Doppler effect and lower BER than other traditional methods.In addition,compared with differential chaos shift key(DCSK)in acoustic channel,the proposed method has lower BER due to using the corresponding matched filter.Due to its security,chaotic signal possesses the potential of improve the performance of Orthogonal Frequency Division Multiplexing(OFDM)system.The chaotic signal generated by the hybrid system can be trivially adjusted to have different base frequencies to fit for OFDM application,and simulation results of the proposed OFDM system using chaotic signal generated by the hybrid dynamical system as carriers show that it has lower BER,compared with traditional OFDM system in additive white gaussian noise(AWGN)channel.