State observers for discrete-time linear systems with unknown inputs

In the paper the problem of designing a full-order state observer for a gen eral discrete-time linear system with unknown inputs is analyzed. Necessary and sufficient conditions for the existence either of an asymptotic or of a deadbeat observer are provided, and a constructive design procedure, toge ther with some examples, are discussed. Finally, the equivalence of these c onditions for problem solvability with those derived in previous contributi ons by means of different approaches is explicitly proved.