Sequence (Viterbi-equivalent) decoding

A decoder for magnetic recording that is applicable to both a (0,3) code equalized and dicode channel and a (1,7) code equalized to a class-IV partial response channel is described. The decoder makes a decision after examining samples from a finite number of bits rather than one bit at a time. It is functionally equivalent to a specific type of Viterbi decoder. The decoder algorithm is significantly simplified by using knowledge of the run-length code constraints. Hardware sharing further reduces implementation complexity. A detailed description of the sequence-decoder algorithm and hardware implementation is given. Test results for both the (0,3) and (1,7) modulation codes at recorder densities of 24690 and 30480 fci (21946 and 40640 bpi) are included. Comparisons are made between the sequence-decoder and peak and threshold detection (bit-by-bit hard decision) for both the actual recording channels and a linear-filter channel simulator