Research On Multiple User Chaotic Shift Keying Technology In Chaotic Digital Communication System

The two most representative systems of chaotic digital communication systems are Differential Chaos Shift Keying(DCSK)and Correlation Delay Shift Keying(CDSK).The DCSK system transmits chaotic carriers in the reference time slot and bit data in the information slot,so the transmission rate is relatively low.The CDSK system overlaps the reference signal with the information signal in one time slot.Then the transmission rate is improved but more interference items are introduced therefore deteriorating the bit error rate(BER)performance at the same time.Currently,communication systems based on multiple user generally have poor BER performance.To improve the BER performance of multiple user systems,three multiple user systems are studied in this thesis,the theoretical BER formula of system under Additive White Gaussian Noise(AWGN)and Rayleigh fading channel is derived by GA method,and analyzed by Monte Carlo experiments.The main contents of this thesis are as follows:1.Due to the poor BER performance of the multiple user system,a Multiple User Noise Reduction DCSK(MU-NR-DCSK)system is studied.The system increases the transmission rate by a reference signal followed by multiple information signals.The system reduces the variance of the noise term by the moving average filter to improve the BER performance at the receiver.Compared with the traditional DCSK,the system is analyzed to increase the data rate and save the bit energy.With the increasing of the number of users,the system doubled transmission rate.And compared the BER performance with other systems,finally the effected of each parameter on BER performance of system is analyzed.2.In order to further improve the transmission rate of MU-NR-DCSK system,an improved MU-NR-DCSK system is studied.The improved system combines all user information and transmits in one information signal,and the different user information signals are distinguished by different Walsh code.The receiver uses a moving average filter to improve the BER performance.The transmission rate of the improved system is(7)N-1(8)2 times than MU-NR-DCSK system.And compared the BER performance with other systems,finally the effected of each parameter on BER performance of system is analyzed.3.Combining the two methods to improve the transmission rate,a Multiple User Orthogonal Differential Chaos Shift Keying(OMU-DCSK)system is studied.The system increases the transmission rate by a reference signal and multiple information signals,each information signal transmits the sum of multiple information,the different user information signals are distinguished by Walsh code.At the same time,an Orthogonal Chaotic Generator(OCG)is used to completely eliminate the intra-signal interference and improve the BER performance of the system.The BER performance and data transmission rate are comprehensively analyzed by the number of delay lines and the number of users.The effected of different combination on system BER performance and transmission rate is analyzed,finally compared the BER performance with other systems.