Distance spectra for PRML channels

Distance spectra for partial response maximum likelihood (PRML) channels are computed by finding generating functions for their error state diagrams. A matrix oriented technique for calculating the generating function is discussed that is reasonable for systems with a relatively small number of states. For those cases where the number of states is larger, a computer search algorithm is described which yields the first few terms of the generating function. Results are presented for channels that are of a form suitable for digital magnetic and digital optical recording. The effect of preceding is also considered.