ADMISSIBILITY OF OBSERVATION FUNCTIONALS

The concept of infinite-time admissibility of unbounded observation fu nctionals is introduced. Under the assumption of exponential stability of the semigroup, it is equivalent to finite-time admissibility recen tly investigated in Weiss (1988 b, 1989). Necessary and sufficient cri teria for admissibility are given. In particular, it is shown that the Ho-Russell-Weiss (1988 b) test for admissibility of observation funct ionals/control vectors can be derived in an elementary way without inv oking the geometric interpretation of the Carleson measure, while the criterion in Weiss (1991) can easily be deduced from the Carleson Embe dding Theorem. Some practically applicable sufficient conditions guara nteeing admissibility are discussed in 3. The results are illustrated by a feedback system containing RLCG transmission line.