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Chaos synchronization and chaos-based secure communication based on new unknown input observer approach

In this paper, the chaos synchronization and chaos-based secure communication is considered when the observer matching condition is not satisfied. The original chaotic system is equivalently transformed into a strongly observability subsystem and a detectability subsystem firstly. Then the exact estimation of the states and the unknown inputs of the strongly observability subsystem are obtained by using the high-order sliding mode differentiator. By these estimations, the states of the detectability subsystem can be asymptotically estimated. Comparing with the existing literature, the chaos synchronization method developed in the present paper can work only under the single strongly detectability condition and the observer matching condition is not needed to be satisfied any more. Finally, one numerical simulation is given to verify the effectiveness of our method and show its superiority to the existing methods.