COVARIANT TIME-FREQUENCY REPRESENTATIONS THROUGH UNITARY EQUIVALENCE

We propose a straightforward characterization of all quadratic time-fr equency representations covariant to an important class of unitary sig nal transforms (namely, those having two continuous-valued parameters and an underlying group structure), Thanks to a fundamental theorem fr om the theory of Lie groups, we can describe these representations sim ply in terms of unitary transformations of the well-known Cohen's and affine classes.