Digital channels

We propose a new class of models of digital communications channels. This class is rich enough to include recursive, nonlinear channels as well as the usual linear finite and infinite impulse response structures. We develop this class to allow for oversampling (in the sense that the channel output is sampled at an integer multiple of the input baud rate) and state theorems which give necessary and sufficient conditions that the channel output can be used to recover the input sequence unambiguously.