Some issues about multirate systems and signals are reviewed in this contribution. First, different models for these signals and systems are considered. Discrete time sequences or blocks of data structured in a sequential or shifted form, allow the representation of signals sampled at different sampling rates, all of them being globally periodic. Process models dealing with sequences or blocks of data can be used to represent multirate scenarios. These models will also lead to a number of appropriate control design techniques. For the analysis and design of multirate controllers, different approaches are considered, such as the discretization of continuous time designed controllers or the direct design of multirate controllers. These techniques are compared and some properties and drawbacks are highlighted. In particular, the ripple in the intersampling behaviour of the controlled system, considered as an unavoidable drawback of multirate controllers, is also investigated.
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