On Observability of Nonlinear Discrete-Time Fractional-Order Control Systems

Nonlinear discrete-time control systems of arbitrary fractional order are studied. This class extends the standard discrete-time systems. Various concepts of observability defined for standard discrete-time systems are transferred to the systems of fractional order. Observation space of the system is defined and used to characterize the indistinguishability relation and different observability properties. Two-dimensional nonlinear system with one output function that depends only on one state variable is studied in detail. In particular, it is studied how the orders of the state equations influence the rank condition that implies local observability.