Stability Analysis and Dynamic Quantizer for Controller Encryption

This study formulates a quantizer design problem for controller encryption and proposes static and dynamic quantizers for the solution to this problem. The proposed quantizers achieve asymptotic stability of networked control systems with the encrypted controller by changing a scaling parameter. The scaling parameter of the dynamic quantizer depends on the plant dynamics and it is updated only by the plant state. Therefore, confidentiality of the encrypted control systems is maintained even if they use the proposed dynamic quantizer. Furthermore, this study also introduces the conditions whereby overflow or underflow of the quantizers does not occur. Finally, a numerical example confirms that the quantizers achieve asymptotic stability of a MIMO system with the encrypted state feedback controller.