Application of distance enhancing codes

During the past few years, significant progress has been made in defining h igh capacity constraints which prohibit specified differences between const rained sequences, thus ensuring that the minimum distance between them is l arger than for the uncoded system. However, different constraints which avo id the same prescribed set of differences may have different capacities, an d codes into such constraints may have different complexity of encoder/deco der architecture and different performance on more realistic channel models . These issues, which have to be considered in application of distance enha ncing codes, are discussed here. We define several distance enhancing const raints which support design of high rate codes. We also define weak constra ints for which the minimum distance between sequences may be the same as fo r the uncoded system but the number of pairs of sequences at the minimum di stance is smaller. These constraints support design of even higher rate cod es. We discuss the implementation issues of both types of constraints as we ll as their performance on the ideal channel and channels with colored nois e and intertrack interference.