On Fault Tolerant Synchronization Control Methods Of Chaotic Secure Communication Systems

Chaos is a kind of special complicated nonlinear systems since it has the characteristics of sensitivity to initial values and high unpredictability, which attracts great attentions from investigators. Since1990s, chaotic synchronization phenomena have been observed in more and more fields. Chaotic synchronization has been developed very quickly as an important research field in chaotic science, and especially, the application in secure communication got great progress. The faults on sensors, actuators and components occur inevitably in the secure communication based on chaotic system, therefore it would cause chaos circuit working performance dramatically down or even cause the entire communication system paralysis and bring huge economic loss. So the reliability of chaotic system is the key to secure communication. Therefore, fault tolerant synchronization for chaotic system has been led to greater attention and became one of the advanced objectives in chaos control field. In the thesis, the problems of fault tolerant synchronization for chaotic systems are studied based on the faults of chaotic secure communication systems. The main research contents are given as follows.Firstly, the problem of H∞robust fault tolerant synchronization control is discussed for a class of chaotic system with state time delay and input time delay. Based on Lyapunov stability theory and LMI(linear matrix inequality) toolbox, an actuator failure matrix is introduced in the case of actuator fault and external disturbance in the system. The sufficient conditions for existence of desired robust fault tolerant synchronization controller are obtained, which are independent on time delay. The H∞performance index y is satisfied by the conditions and the robust stability of the system is assured. And the simulation results show that the useful signal can be recovered from the receiver effectively.Secondly, the problem of non-fragile fault tolerant synchronization control is discussed for a class of chaotic system with time-varying delay and uncertainties. Based on Lyapunov stability theory and LMI toolbox, the sufficient conditions for existence of desired non-fragile fault tolerant synchronization controller are obtained for the system against actuator fault, which are dependent on time delay, and guaranteed cost performance is satisfied. Then, the proposed synchronization control method is applied to the chaos secure communication system and is validly confirmed by simulation results.Thirdly, based on the adaptive observer, the problem of chaotic fault tolerant synchronization control is discussed with system sudden fault. Using adaptive observer not only can be utilized to give a real time diagnosis of the fault, but also can realize the synchronization of chaotic system. The synchronization of the chaotic system is proved by Lyapunov theory both in normal case and in fault case. The numerical simulation results verify the effectiveness of the proposed schemes. Based on the synchronization platform, the communication signals can be masked completely by the chaos signal.Finally, the conclusion is given and some open problems are also discussed.