Chaotic Synchronization Control And Its Applications To Secure Communication

Chaos is a special moving form of nonlinear dynamics system, whose trajectory of the orbits in the phase plane is very complex, pseudorandom, and can be observed in fairly simple dynamical systems. Chaotic signal has the properties of ergodic, nonperiodic, continuous broadband power spectra, and noise like etc. These properties coincide with the requirements for signals applied in secure communication systems. Along with the appearance of chaotic synchronization methods, chaotic system synchronization and its applications in secure communication have aroused the attention of people. How to find the best scheme of synchronization is becoming today's hotspot and difficulty of research.Based on the theories of nonlinear control and stability analysis, this dissertation studies the ways of designing and improving on chaotic synchronization. Then we apply the synchronized systems in secure communication. The main contributions of this dissertation are as follows:Firstly, according to the strategy of adaptive control for parameters, the uncertain parameters of system are identified. Based on Lyapunov stability theory a nonlinear feedback controller is presented, which realizes the good chaotic synchronization. Simulation results show that the method can realize monotonous synchronization and identify the uncertain parameters quickly.Secondly, chaotic synchronization control with diverse structures and uncertain parameters based on a new chaotic system are investigated. We adopt the method of nonlinear control combining with adaptive identification for parameters. This controller can achieve the good chaotic stable synchronization between the different systems.Thirdly, we present a kind of chaos synchronization control technique based on variable structure systems through adaptive sliding mode controller. Simulation results show the proposed scheme's robustness in the uncertain parameters and external noise disturbances. Compared to other chaos controlling methods, this control has better qualities in robustness and transition.Finally, we mainly study three methods in this part of secure communication. It includes the chaos masking, parameter modulation and chaos shift keying. Firstly, based on the theory of tracking control a secure communication system with chaotic masking is designed. Simulation results show it can recover the information signal undistorted. Then, we modulate the formal parameter-modulated system. In the receiver, the information is demodulated by analyzing synchronization error. Lastly, we present a digital secure communication based on hyper-chaos through chaos shift keying. It is more secure because of enhancing the complexity and decrease the correlation of transmitted signals. Meanwhile by designing compound nonlinear function transformation for transmitted signals to further intercalate the secret key, the determined intruders are very difficult to retrieve the contents of message signal using forecasting method. Theoretical analysis and numerical simulation results show that this method is effective.