Art of constructing low-complexity encoders/decoders for constrained block codes

A rate p : q block encoder is a dataword-to-codeword assignment from 2^p p-bit datawords to 2^p q-bit codewords, and the corresponding block decoder is the inverse of the encoder. When designing block encoders/decoders for constrained systems, often, more than 2^p codewords are available. In this paper, as our main contribution, we propose efficient heuristic computer algorithms to eliminate the excess codewords and to construct low hardware complexity block encoders/decoders. For (0,4/4) and (0,3/6) PRML constraints, block encoders/decoders generated using the proposed algorithms are comparable in complexity to human-generated encoders/decoders, but are significantly simpler than lexicographical encoders/decoders