Adaptive Randomized Controller Switching for Resilient Cyber-Physical Systems

A switching based scheme is developed to combine redundant subsystems in controller implementations for cyberphysical systems (CPSs) to increase resiliency to adversarial modifications of a subset of the redundant subsystems. A time-division multiplexer is introduced to select, at each time instant, one of the outputs of multiple controller implementations and pass it through as the input to the physical system being controlled. We show that the proposed time-division multiplexing enables limiting the impact to stability and performance of the closed-loop CPS due to adversarial modifications of a subset of the controllers. Furthermore, we show that by making the switching between controllers probabilistic rather than round-robin and by adapting the probabilities of switching to each of the controllers on-line, the adversarial impact to the CPS can be attenuated over time. The efficacy of the proposed approach is shown through simulation studies on an illustrative example of a single-machine-infinite-bus system.