Note on stability of discrete-time time-varying delay systems

This note is concerned with the problem of delay-dependent stability for discrete-time systems with time-varying delay. Two novel delay-dependent stability conditions are established by bounding the forward difference of the Lyapunov functional based on the reciprocally convex approach and a scale inequality, respectively. These criteria improve the existing ones with smaller computation burden and less conservatism, which is verified by both theoretical proof and a numerical example.