Combi-codes for DC-free runlength-limited coding

We present a new coding scheme for DC-free runlength-limited (RLL) codes. T his scheme is based on the combination of two codes, a main code and a subs titution rode, both operating on symbols of a fixed length n. The substitut ion code has a special structure, i.e., for each n-bit symbol there are two possible channel words, which have opposite parity and the same next-state in the underlying finite-state machine (FSM). The advantages of this syste matic structure of the code are: guaranteed DC-control, ECC-symbol oriented coding, and low-complexity look-ahead DC-control encoding. Both for EFM-li ke RLL constraints (d = 2, k = 10) and for (d = 1, k = 7) RLL constraints, a design for an efficient Combi-Code is outlined.