On Observation of Time-Delay Systems With Unknown Inputs

Causal and non-causal observability are discussed in this technical note for nonlinear time-delay systems with unknown inputs. Using the theory of non-commutative rings and the algebraic framework introduced by Xia , the nonlinear time-delay system is transformed into a suitable canonical form to solve the problem. A necessary and sufficient condition is given to guarantee the existence of a change of coordinates leading to such a form.