Simple classes of constrained systems with unconstrained positions that outperform the maxentropic bound

The Wijngaarden-Immink (WI) scheme is a combined modulation/ECC coding scheme, where arbitrary user data are translated into a constrained sequence in which predefined positions are reserved for ECC parity. Besides offering the benefit of combined modulation/ECC coding, the WI scheme has two extra benefits. They are a) error propagation is limited to the constrained symbols, since symbols on the unconstrained positions are not related, and b) code hardware is limited to a look-up table of the coded part. We will describe classes of simple bit-stuffing schemes that require less redundancy than predicted by the bound based on the performance of maxentropic constrained systems presented by Campello et al. [1] and Poo et al. [21].