Research And Improvement Of Multiuser DCSK System In Chaotic Communication

As one of the main applications of chaos in the field of digital communication,chaotic digital modulation technology has aroused extensive attention because of its good security and anti-interference.The chaotic keying communication system based on coherent detection needs to generate a synchronous copy of the chaotic signal at the transmitter.Because the robust chaotic synchronization problem is difficult to solve,the current research is mainly focused on the chaotic keying communication system based on incoherent detection.Differential Chaos Shift Keying(DCSK)system,as one of the typical systems of incoherent detection,has better bit error performance than Correlation Delay Shift Keying(CDSK)system.However,due to the structural defects of the DCSK system,the signal cannot be sent continuously,so the transmission rate is unsatisfactory.In order to further improve the transmission rate of DCSK system and reduce the bit error rate(BER)of multiuser DCSK system,several improved systems are proposed.The main research contents of this paper are as follows:1.Aiming at the low transmission rate of DCSK system,an Orthogonal Multiple User Noise Reduction DCSK(OMU-NRDCSK)communication system is proposed.Through different delays,the duplicated chaotic sequence at the transmitter of the system carries multiuser's information modulated by orthogonal Walsh code,which improves the transmission rate of the system,and reduces the variance of the noise terms by averaging the received signal.The Gaussian Approximation(GA)method is used to derive the theoretical BER of the system in the Rayleigh channel,and the system performance is analyzed under different parameters.The results show that the system can increase the bit transmission rate while reducing the bit error rate.2.In order to further improve the error performance of OMU-NRDCSK system,a Novel Noise Reduction DCSK based on Quadrature Modulation(QM-NRDCSK)communication system is proposed.The two signals of the system are transmitted in the same frequency band using orthogonal modulation,and the chaotic sequence of the transmitter is modulated after different delay in each route.The theoretical BER formula of the system is derived in the Rayleigh channel,and the system performance is analyzed under different parameter conditions.The results show that the spectrum utilization rate of the system has been improved,and the system has better error performance.3.In order to improve the poor bit error performance of DCSK system due to multi-level transmission of multiuser and M-ary information,a Multiuser Orthogonal Multilevel DCSK(MOM-DCSK)communication system is proposed.The M-ary information to be transmitted by the system is mapped into different transmission coefficients,which are respectively multiplied by mutually orthogonal Walsh codes and added together for transmission,and different user's information is transmitted through different time slots with different delays.The theoretical BER formula of the system is derived under the Rayleigh channel,and the simulation analysis is carried out.The results show that the system still shows good bit error performance with the increase of transmission base number.