Time-varying lag smoothing with intermittent unknown inputs: A defense strategy against deception attacks

This paper presents an optimal time-varying lag smoothing for left invertible linear discrete-time systems subject to intermittent unknown inputs. The use of the proposed filter, expressed as an augmented state Kalman filter updated online from the intermittent unknown inputs estimate, is illustrated in the area of networked control systems subject to deception attacks on the control signal transmitted by the controller to the plant. Stochastic stability conditions of the filter are established when the arrival sequence of the attacks follows independent Bernoulli random variables.