| The randomness and unpredictability of chaotic signals,as well as its advantages in resisting frequency selective fading and narrow band interference which makes chaotic signals meet the demand of secure communication perfectly.Chaotic digital keying technology is a hot-spot research content in chaotic secure communication,in which the Differential Chaos Shift Keying(DCSK)system is a typical scheme.Using Transmitted Reference(T-R)mode can help to reduce the interference between the reference signal and its information signal in DCSK,thus raising the bit error performance of DCSK.However,using T-R mode also brings the disadvantages such as low transmission rate and poor energy efficiency in DCSK.To meet the requirements of modern wireless communication systems,the following three solutions are studied in this thesis:1.In order to reduce the time redundancy in transmitting reference signal,raising the energy efficiency and transmission rate of DCSK,an Orthogonal Multi-User Short Reference Differential Chaos Shift Keying(OMU-SR-DCSK)system is studied.The OMU-SR-DCSK system uses two delay units to different two information slots.In each information slot,the information bearing signals,realized by repeating the reference signal for P times,modulate N information bits by using Walsh codes.The orthogonality of Walsh codes can eliminate the interferences between users.An Approximation Gaussian(GA)method is used to deduce the Bit Error Rate(BER)formula of OMU-SR-DCSK system under two-path Rayleigh fading channel,and the Monte Carlo simulations are also carried out to verify the effectiveness of the OMU-SR-DCSK system,in terms of energy efficiency,transmission rate and bit error performance.2.In order to solve the problem that the bit error performance of multi-user DCSK system deteriorates due to the interference among users when the number of user increases,thus an Orthogonal Multi-User Noise Reduction Differential Chaos Shift Keying(OMU-NR-DCSK)system is studied.The system differentiates N information slots with N different delay times,and introduces Hilbert transformation in each information slot to double the transmission rate without introducing interferences between users.At the receiver,the moving average filter is employed to denoise the received signal to improve the bit error performance.The BER formula of OMU-NR-DCSK system under multi-path Rayleigh fading channel is derived by using GA method,and the BER formula under Additive White Gaussian Noise(AWGN)channel is also derived.The Monte Carlo simulations under the two channels are further carried out to verify the validity of the improved scheme.3.In order to solve the problem of low transmission rate of traditional multi-user DCSK systems caused by using serial transmission mode to transmit information bits,as well as high complexity of the system caused by using multiple delay units and switches.Combining with the Multi-Carrier Modulation(MCM)technology,a Quadrature Multi-Carrier Noise Reduction Differential Chaos Shift Keying(QMC-NR-DCSK)system is proposed.The system uses M carriers with different center frequencies to transmit information bits,and at the same time uses the Quadrature Modulation(QM)technology to shift the phase of all the M carriers for 90°.Using the M orthogonalized carriers to transmit information bits can double the transmission rate.Aiming at enhancing the bit error performance,a filter is introduced at the receiver for noise reduction.Besides,an improved system,naming Improved Quadrature Multi-Carrier Noise Reduction Differential Chaos Shift Keying(IQMC-NR-DCSK),is studied by introducing switches into QMC-NR-DCSK system,which further optimizes the energy efficiency,frequency band utilization and the transmission rate.By using GA method,The BER formula of QMC-NR-DCSK and IQMC-NR-DCSK system under multi-path Rayleigh fading channel are deduced,and the Monte Carlo simulations are accomplished respectively.Comparisons between the two system and other multi-carrier DCSK systems verify that the transmission rate,bit error performance and energy efficiency are significantly enhanced. |
PDF Full Text Request