Research On Multi-Carrier Differential Chaos Shift Keying Modulation Over Underwater Acoustic Channels

Due to the important military and economic strategic position of oceans,people are paying more and more attention to the research of marine technologies.The development of marine resources poses a major demand for marine communications.As the most stringent and complicated channel,underwater acoustic(UWA)channels are featured by high multipath interference,severe Doppler spread,high noise,and narrow bandwidth.Thus,it is important to study robust communication systems over UWA channels.For the time-varying and frequency-varying problems of UWA channels,this thesis proposes two novel multi-carrier differential chaos modulation systems,which combines code shifted differential chaos shift keying(CS-DCSK)with orthogonal frequency division multiplexing(OFDM).The main contributions of this thesis are summarized as follows:(1)We propose a new multi-carrier chaos modulation scheme,namely multi-carrier code shifted differential chaos shift keying I(MC-CS-DCSK-I).The proposed system first superimposes the chaotic reference chips and the information bearing chips in the same time/frequency domain,but orthogonal in the code domain,which makes the signals have good robustness in time-varying channels.Then all chips of the CS-DCSK symbol are loaded on different subcarriers to further enhance the capacity of resisting inter-symbol interference(ISI).Compared with the CS-DCSK system and multi-carrier differential chaos shift keying(MC-DCSK)system,the MC-CS-DCSK-I has a more excellent ability to resist time-frequency doubly selective fading of channels.Finally,the proposed system is applied to the UWA channels,which exhibits good robustness.(2)To overcome the problems of low spectrum efficiency and lack of flexibility of the MC-CS-DCSK-I system,we propose a multi-bit parallel multi-carrier code-shifted chaos modulation system(multi-carrier code shifted differential chaos shift keying II:MC-CS-DCSK-II).The proposed system decouples the number of subcarriers and the spreading factor,which enhances the flexibility of the system and improves the utilization of the bandwidth.We study the BER performance of the system under time-frequency doubly selective fading channels and compared with the traditional multi-carrier direct spread spectrum(MC-DSSS)systerm and MC-CS-DCSK-I system.Simulation results show that the system has superior performance than MC-DSSS and MC-CS-DCSK-I in certain Doppler shift range.Finally,when the system is simulated in UWA channels,it also shows good robustness.(3)To the in-depth understanding of the two systems,the bit error rate of MC-CS-DCSK-I/II systems under Gaussian channels and multipath Rayleigh fading channels are derived by Gaussian approximation,which verifies the feasibility and effectiveness of the systems.Finally,the peak to average power ratio performance,spectrum efficiency and complexity of MC-CS-DCSK-I and MC-CS-DCSK-II are analyzed,and the advantages of the two systems are summarized.