Partial-response decoding of rate 1/2 modulation codes for digital storage

In digital storage systems, receivers for rate 1/2 modulation codes are usually oversampled by a factor of two with respect to the data stream that they attempt to reconstruct. It is shown that oversampling may be avoided by using partial-response techniques to detect, instead of the encoded binary signal, a decimated ternary one, from which the original data can be recovered by means of a simple decoder. A method is described to find all such decoders for a given rate 1/2 code. Examples treated are FM, MFM, Miller-squared, (2,7), 3PM, and quad-phase. The mean-square performances of these reception schemes are analyzed and compared to those of their predecessors for a Lorentzian channel. The relative merits are found to depend quite heavily on the information density, favoring some of the studied schemes at high densities