Application of distance enhancing codes

During the past few years, significant progress has been made in defining high capacity constraints which prohibit specified differences between constrained sequences, thus ensuring that the minimum distance between them is larger than for the uncoded system. However, different constraints which avoid the same prescribed set of differences may have different capacities, and codes into such constraints may have different complexity of encoder/decoder architecture and different performance on more realistic channel models. These issues, which have to be considered in application of distance enhancing codes, are discussed here. We define several distance enhancing constraints which support design of high rate codes. We also define weak constraints for which the minimum distance between sequences may be the same as for the uncoded system but the number of pairs of sequences at the minimum distance is smaller. These constraints support design of even higher rate codes. We discuss the implementation issues of both types of constraints as well as their performance on the ideal channel and channels with colored noise and intertrack interference.