Research Of Chaos Synchronization And Its Application In Communication

Knowledge on chaos is one of important achievements in nonlinear science. With the further research of chaos,chaos control becomes an advanced research field. Chaos synchronization belongs to chaos control in general,and it has become important content of chaos control. Because chaotic signal has characteristic of broad bandwidth and like-noise,chaos has potential application in secure communication system. This dissertation extends theoretical foundation and offers theoretical method of chaos synchronization and its application in secure communication.The dissertation discusses systematically basic concepts,main feature,measure,research method and classification of chaos,and theoretical foundations of utilizing chaos in communication system are investigated briefly.Considering the discord of definition of chaos synchronization and different problems in practice,the author offers his definition of chaos synchronization,and classifies them based on the definition,which establishes foundation to research it systematically and profoundly.As groundwork of controlling chaos system,it is first time to offer controllability and observability of chaotic system utilizing difference geometry theory,taking typical Lorenz chaos as example. The conclusion on Lorenz system is given,and the research method of other chaotic systems are provided at the same time.A kind of synchronization technique is presented based on variable structure system (VSS) control theory and above conclusion in the dissertation. Chaos synchronization problem is particular with two points,that is,both the thickness of sliding mode field at equilibrium point and output of controller at equilibrium point should be zero. A scalar VSS controller is designed,and simulation results show that the synchronization technique is effective. A kind of secure communication system scheme is presented,which utilizes VSS synchronizing controller to demodulate. Amplitude masking modulation and spread spectrum modulation are considered to validate feasibility of the presented scheme. Simulation results show that it is effectiveness and the synchronization technique is robust.Using quasi-stochastic property and ergodic theory of chaos,a kind of new hybrid DS/SFH spread spectrum communication scheme is presented based on VSSsynchronization technique. Chaotic spread spectrum sequences,including direct sequences (DS) and frequency hopping (FH) sequences are designed utilizing Chebvshev map chaotic system. It is proved in theory the designed chaotic sequences are not only meet the request for spread spectrum sequences,but also have advantage of bigger number than other coding techniques,good correlation property and broad FH interval property and good balance property. To verify the performance of DS sequence,a kind of correlation detector is designed,and its BER formula is derived. Simulation results demonstrate theoretical derivation is correct and both sequences can be used in communication.Based on the presented DS/SFH communication scheme,and employing MSK as FH spread spectrum modulation,the performance is studied n the presence of partial band multitone jamming and additive white Gaussian noise (AWGN). Supposing chaotic DS-spread spectrum signal bandwidth is equal to the FH slot spacing,the bit error rate formula is derived,and its performance is evaluated and simulated assuming the worst case of jamming strategy. The results show that,in some cases,the addition of chaotic DS spreading to FH system,without increasing total system bandwidth,can improve significantly the system's resistance to partial band multitone jamming.Many chaos secure communication systems presented in literatures is designed based on APD method,and some scheme take the system parameter as key. The author discovers that it has potential insecurity because low-dimensional system can be reconstructed easily. It is necessary to adopt high-dimensional spatiotemporal chaotic system in order to enhance security and improve anti-deciphering performance of secure communication syst...