Research On Chaotic Digital Modulation Technologies Based On DCSK

Transmitted-reference(T-R)mode is used in differential chaos shift keying(DCSK).The binary data bit is indicated by the same or opposite phase between the reference signals and the information-bearing signals.The correlation demodulation method is utilized in the receiver without synchronization of spreading code and channel estimation.DCSK not only has the excellent characteristics of chaotic signals,but also has the properties,such as the simple structure of transceiver,anti-multipath interference ability.However,there are some fixed zero points for the square amplitude spectrum of DCSK signals caused by the T-R mode,and the data transmission rate is low.Most of the existing single user or multiuser modulation schemes have this features of DCSK.Gaussian approximation(GA)method and Monte Carlo simulation method are used as analytical tools to deeply study three kinds of improved modulation schemes based on DCSK.The main contents of this thesis are given as follows:1.For existing defect of low data transmission rate in DCSK,the improved modulation scheme called CD-DCSK is studied.The advantages of DCSK and correlation delay shift keying(CDSK)are combined in this scheme.To realize the constant signal energy in different bit periods,the chaotic sequence is mapped into binary chaotic sequence by introducing a symbolic function.At the receiving end,correlation demodulation technique is employed in two parallel demodulation modules at the same time,and the data bits can be restored.The BER formula of CD-DCSK in AWGN channel is deduced,and the relationship between length of chaotic sequence and BER is analyzed emphatically.The Monte Carlo simulation is utilized to validate the theoretical derivation,and the BER performance of CD-DCSK is compared with DCSK and CDSK.Analysis and simulation results show that the data transmission rate of CD-DCSK is twice that of DCSK and the fixed zero points in square amplitude spectrum are removed with a slight sacrifice on BER performance.2.To improve the BER performance of reference-modulated DCSK(RM-DCSK),RM-DCSK based on orthogonal chaotic signals(ORM-DCSK)is studied.The strictly orthogonal chaotic signal is used as the carrier to eliminate the interference term in the decision variable by designing an orthogonal chaotic signal generator.The new scheme expands the frame structure of RM-DCSK and reduces the average bit energyeffectively.The BER formula of ORM-DCSK in AWGN channel is deduced.Furthermore,the BER formula of MISO-ORM-DCSK in multipath Rayleigh channel is deduced to study the validity of ORM-DCSK in Multiple-input and Single-output(MISO),and the relationship between the system parameters and BER is analyzed.Analysis and simulation results show that ORM-DCSK has better BER performance than RM-DCSK at any signal-to-noise ratio without sacrificing RM-DCSK transmission rate.Besides,this BER enhancement appears to be more and more obvious when the number of timeslots becomes greater in a given range.Nevertheless,the ORM-DCSK is more complex than RM-DCSK.In MISO,ORM-DCSK still has better BER performance than RM-DCSK.3.There are many weaknesses in existing multiuser DCSK(MU-DCSK)schemes,such as multiuser interference and undistinguished BER performance.To improve BER performance,the MU-DCSK based on orthogonal chaotic carrier(OMU-DCSK)system is studied.By introducing an orthogonal chaotic signals generator with Hadmard matrix,the multiuser interference is eliminated.Reference signal is used by all users,which reduces the average bit energy effectively.The BER formula over multipath Rayleigh fading channels is derived by GA method and numerous simulations and contrast experiments are worked.Theoretical analysis and simulation results show that the proposed system has superior BER performance with a slight cost in complexity.