A 2-TRACK MATCHED SPECTRAL-NULL CODE WITH RATE 3/4 FOR THE BINARY DICODE CHANNEL

Matched spectral-null modulation codes were recently introduced as a method to improve the reliability of digital data storage in digital recording systems. These codes are also dedicated to noisy partial-response channels with input alphabet of finite size. We present here a two-track matched spectral-null code of rate 3/4 derived from the cross product of two canonical diagrams that characterize sequences with a spectral null at zero frequency. This code provides a 3 dB distance gain over the dicode channel and limits to 1 the maximum runlength of zero samples at the output of the channel. It is also designed to perform simple two-track by two-track maximum-likelihood detection in the presence of severe additive intertrack interference. Its implementation incorporates a 4-state encoder, a 12-state Viterbi detector and a state-independent sliding-block decoder.