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

A rate p : q block encoder is a dataword-to-codeword assignment from 2p p-bit datawords to 2p 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 2p 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.