Many practically important linear systems are
slowly time-varying. In this paper we consider the frequency-domain identification of
slowly time-varying systems
with limited impulse response (underspread systems). We review time-frequency
representations of LTV systems and its connection to the Gabor expansion of
signals. It is shown how the matched multiwindow Gabor expansion can be used for the
optimum frequency-domain identification and canonical realization of
underspread LTV systems.