This paper studies robust stability analysis of discrete-time linear periodically time-varying (LPTV) systems. We consider employing the cycling technique for treating LPTV systems, and give a robust stability condition in the cycling-based framework. Then, cycling-based causal/noncausal LPTV scaling can be introduced, and this paper discusses its relationship to and differences from lifting-based causal/noncausal LPTV scaling for developing a basis of a cycling-based scaling approach. An insight into robust linear time-invariant controller synthesis for LPTV plants is also given. © 2011 SICE.