Research On Multiple User Chaos Shift Keying Communication Systems

As one of the most widely studied communication technologies in the past thirty years,chaotic keying communication system is represented by Differential Chaos Shift Keying(DCSK)and Correlation Delay Shift Keying(CDSK).Because of the adoption of Transmitted-Reference(T-R)mode,DCSK shows good Bit Error Rate(BER)performance,but it has the disadvantage of low data transmission rate.And CDSK system's data transmission rate is twice that of DCSK system,but its BER performance is clearly inferior to that of DCSK.As the two communication systems don't need to establish chaotic synchronization at the receiver,they have been widely recognized and researched by scholars of various countries.In order to meet the demand of modern communication and further improve the information transmission rate,multi-user access technology is an important development trend of current chaotic communications.At present,a variety of multi-user chaotic keying communication systems based on DCSK and CDSK were proposed by scholars worldwide,but most of the systems have low BER performance.To further improve the BER performance of the existing multi-user chaotic key communication schemes,the thesis focus on how to reduce the interference between different users.The main work of this thesis contains the following points:(1)First of all,the chaos theory and its development are introduced briefly,and the main research technology and current status of chaotic communication are epitomized in the thesis.Then basic theories of chaos are expounded,including the definitions of chaos,the characteristics and the generation of chaotic signals.In addition,the principles of modulation and demodulation of several classical single-user chaotic keying communication systems are introduced in detail,with in depth analysis of their advantages and disadvantages.In the end,a classical multi-user chaotic keying communication system-Variant Delay Multiple Access DCSK(VDMA-DCSK)is introduced,and the system performance is analyzed.(2)Aiming at the poor BER performance and the large need of delay circuits of VDMA-DCSK,this thesis proposed an improved Multi-user Orthogonal Differential Chaos Shift Keying(MU-ODCSK)communication system.In this system,the Walsh code and the symbol function are combined to generate the orthogonal carrier signal at the transmitter,which reduces the interference between different users when the receiver is demodulated.Exact BER formulas of MU-ODCSK are separately derived under Additive white Gaussian Noise(AWGN)channel and Rayleigh fading channel,and simulation verification and performance analysis is conducted.Simulation results show that the BER performance MU-ODCSK is more excellent than the VDMA-DCSK system under the same conditions.(3)A Multi-user Segment Shift Differential Chaos Shift Keying(MU-SSDCSK)communication system is studied.In this system,according to the number of users in transmission,the reference signal of MU-SSDCSK is divided into m segments,which are then shifted and matched with different Walsh codes that therefore can make the information-bearing signals orthogonal to each other.The exact theoretical BER formula of MU-SSDCSK is derived in AWGN channel and simulated.The simulation results show that the MU-SSDCSK communication system can effectively improve BER performance compared with VDMA-DCSK.