Markers to construct DC free (d, k) constrained balanced block codes using Knuth’s inversion

We adapt Knuth’s balancing scheme, which was originally developed for unconstrained binary code words. We present a simple method to balance the NRZ runlength constrained block codes corresponding to (d, k) constrained NRZI sequences. A short marker violating the maximum runlength or k constraint is used to indicate the balancing point for Knuth’s inversion. The marker requires fewer overhead bits and less implementation complexity than indexing the balancing point’s address by mapping it onto a (d, k) or runlength constrained prefix, such as when applying Knuth’s original scheme more directly. The new code construction may be attractive for future magnetic and especially optical recording schemes. In fact the current optical storage media such as the CD, DVD and Blue Ray Disc, all attempt to achieve some suppression of low frequency components of the constrained codes, by exploiting a limited degree of freedom within the set of candidate (d, k) words.