On the existence of robust functional KKL observers

This paper shows the existence of robust functional observers for autonomous dynamical systems that verify a backward-distinguishability condition with respect to the functional to be estimated. Then, we show how those results can be exploited to show existence of asymptotic observers for systems with inputs under appropriate distinguishability conditions, when the input is known to be generated by some finite-dimensional autonomous dynamical system. This is done by considering an extended system made of the plant and the input generator.