New results on stability of discrete-time systems with time-varying state delay

This note is concerned with the stability analysis of discrete-time systems with time-varying state delay. By defining new Lyapunov functions and by making use of novel techniques to achieve delay dependence, several new conditions are obtained for the asymptotic stability of these systems. The merit of the proposed conditions lies in their less conservativeness, which is achieved by circumventing the utilization of some bounding inequalities for cross products between two vectors and by paying careful attention to, the subtle difference between the terms Sigma m=(k-1)(k-dk) (center dot) and Sigma(k-1)(m=k-dM) (center dot), which is largely ignored in the existing literature. These conditions are shown, via several examples, to be much less conservative than some existing result.