Research And Improvement Of Multiuser Correlation Delay Shift Keying Technology

As the modern communication technology develops rapidly,the requirements have been raised which people have proposed for the anti-jamming performance and security of signals transmitted in wireless communication.The emergence of chaotic keying communication technology meets these two requirements to a certain extent.As to chaotic keying communication system,Differential Chaos Shift Keying(DCSK)and Correlation Delay Shift Keying(CDSK)are the two most classical systems.Compared with the DCSK system,the switch structure in the DCSK system is replaced by an adder,which realizes the continuous signal transmission that the DCSK system cannot achieve,and makes the transmitted signals of any two consecutive frames irrelevant,so as to make CDSK system safer than DCSK system.However,the cost of the above advantages is that the interference between signals which leads to the increase of the probability of misjudgment of signals,so that the system error code performance is poor.To improve the poor error performance of CDSK and to apply the system into the multi-user scenario of modern communication,the main research contents of this thesis are as follows:1.Due to the problem of high bit error rate in CDSK system,the Noise Reduction Multi-User Correlation Delay Shift Keying(NR-MUCDSK)chaotic communication system without inter signal interference is studied.Based on CDSK system,walsh code sequence,orthogonal modulation and noise reduction technology is applied in the system.Firstly,walsh code sequence is introduced into the transmitter,which not only makes the reference signal and multi-channel information signal can be overlaped without introducing inter signal interference,but also can replace the delay structure of CDSK system.Secondly,orthogonal modulation is used to double the transmission rate of the transmitter.Finally,the noise reduction technology is used to processe the received signal at the receiver so that the influence of channel noise can be reduce on signal decision.The theoretical Bit Error Rate(BER)of NR-MUCDSK system is deduced in Additive White Gaussian Noise(AWGN)channel and two-path Rayleigh fading channel environment.Afterwards,simulation experiment is used to verify the BER of the system and simulation comparison is conducted with different systems to verify the superiority of system.2.To further improve the transmission rate and BER performance of CDSK system,a Noise Reduction Multi-Carrier Correlated Delay Shift Keying based on schmidt orthogonalization(NR-MC-CDSK)chaotic communication system is studied.Based on CDSK system,N orthogonal chaotic sequences are generated by schmidt orthogonalization as reference signals and walsh code is combined to further improve the transmission rate of the system so that NR-MC-CDSK system can transmit MN user information bits within one frame of signal time.Finally,the noise reduction technology is used to processe the received signal at the receiver.Using the Gaussian Approximation(GA)method,the theoretical BER of NR-MC-CDSK system under different channel conditions is deduced.The correctness of theoretical BER formula is verified by simulation software.Then the influence of system parameters on BER performance is studied and compared with other multi-carrier chaotic communication systems to verify the superiority of system.3.In order to improve the disadvantages of poor BER performance in traditional multi-user CDSK systems,a Noise Reduction Improved Multi-Carrier Correlated Delay Shift Keying(NR-I-MC-CDSK)chaotic communication system is studied.In this system,the chaotic signal generator is improved at the transmitter and the chaotic sequence is processed by the editor so that the chaotic signal generator can produce two orthogonal chaotic sequences.In addition,the number of transmission bits within a single signal duration can be further improved by using multicarrier technology in the system.At the receiver,the moving average filter is used to reduce the proportion of noise interference part in the decision variable so that the purpose of improving BER performance can be achieved.The theoretical BER of NR-I-MC-CDSK system in AWGN channel and multi-path Rayleigh fading channel is derived and compared with other multi-carrier chaotic communication systems in the simulation experiments to verify the superiority of system.