An 8/9 rate time-varying trellis code for high density magnetic recording

A simple time-varying trellis code constraint is introduced which achieves 2.2 dB coding gain with the EEPR4 partial response target in additive white Gaussian noise. The capacity of this 'Tribit Mod 2' (TM2) constraint is 0.9163. A block code construction and a practical 8/9 rate block code of length 9 with an RLL k=11 constraint is detailed. Quasi-catastrophic events are described in NRZI space and are shown to be coded out of the 8/9 code. The TM2 code's effective minimum distance including noise coloration effects is analyzed, and shows that coding gain is achieved at high channel densities with the EPR4 partial response target as well as with the EEPR4 and maximum likelihood targets.