An alternative construction of interleaved RLL codes for partial response channels using multichannel methods

Current work in magnetic recording channels has demonstrated significant improvement in recording density using partial response communication methods along with maximum likelihood detection. The class IV partial response channel (PR4) behaves as the interleaving of two identical run-length limited (RLL) channels. Efficient recording codes for the PR4 channel have been made by considering a channel bit sequence to be composed of two interleaved subsequences. Finite state techniques are used to describe run-length constraints on each subsequence as well as a global run-length constraint on both sequences combined. A recent paper by Swanson and Wolf discusses multichannel run-length limited codes that turn out to be very similar to interleaved run-length limited codes. The present paper discusses the similarities between the code description of multichannel RLL codes and the interleaved RLL codes required by the PR4 channel. The extension of the techniques of multichannel RLL work to the interleaved problem is discussed. It was found that suitable code constructions are possible by viewing the problem as two distinct RLL codes that have individual maximum run-lengths onto which a global run-length is imposed. Two examples are developed to illustrate the ideas