  We consider discrete-time (DT) systems S in which a DT input is first
tranformed to a continuous-time (CT) format by phase-amplitude modulation, then
modified by a non-linear CT dynamical transformation F, and finally converted
back to DT output using an ideal de-modulation scheme. Assuming that F belongs
to a special class of CT Volterra series models with fixed degree and memory
depth, we provide a complete characterization of S as a series connection of a
DT Volterra series model of fixed degree and memory depth, and an LTI system
with special properties. The result suggests a new, non-obvious, analytically
motivated structure of digital compensation of analog nonlinear distortions
(for example, those caused by power amplifiers) in digital communication
systems. Results from a MATLAB simulation are used to demonstrate effectiveness
of the new compensation scheme, as compared to the standard Volterra series
approach.
