Performance comparison of selected DC-free codes for PR1-equalized magnetic recording channels

Assuming the Lorentzian channel model and linearity, we compare the performance of various DC-free codes combined with PR1 signaling on the magnetic recording channel. In addition to several codes which have been presented in the literature, we consider two high rate DC-free codes (rates 8:9 and 16:18) which we have designed for the PR1 situation. Two types of Viterbi receivers are examined: one whose trellis is matched to the PR1 channel, and another whose trellis is matched to the combined trellises of the PR1 channel and the code constraint. Our results demonstrate that high rate codes with a loose charge constraint (narrow spectral null) are to be preferred over lower rate codes with a tight constraint (wide null). We also demonstrate that the rate 16:18 code, which possesses both a high rate and a tight constraint (charge Q is bounded as |Q|⩽4), offers the best performance among the codes considered