Asymptotic output tracking of fully input-output linearizable systems via output feedback

We study the asymptotic output tracking control of fully input-output linearizable nonlinear systems in a case where the full state of the system is not available. The main purpose of the paper is to show the following two facts : 1) if a single-input single-output (SISO) nonlinear system has relative degree n, then there always exists a state observer for the given nonlinear system which guarantees the observation error converges to zero exponentially; and 2) if a SISO nonlinear system has relative degree n, then there always exists an output feedback controller which guarantees the tracking error is less than the prescribed bound and converges to zero asymptotically.