Non-Uniform in Time Robust Global Asymptotic Output Stability for   Discrete-Time Systems
  In this paper the notions of non-uniform in time Robust Blobal Asymptotic Output Stability (RGAOS) and Input-to-Output Stability (IOS) for discrete-time systems are studied. Characterizations as well as links between these notions are provided. Particularly, it is shown that a discrete-time system with continuous dynamics satisfies the non-uniform in time IOS property if and only if the corresponding unforced system is non-uniformly in time RGAOS. Necessary and sufficient conditions for the solvability of the Robust Output Feedback Stabilization (ROFS) problem are also given. 
Iasson Karafyllis