On Viterbi detector path metric differences

This letter continues the investigation of methods for computing exact boun ds on the path metric differences in maximum-likelihood sequence detectors based upon the Viterbi algorithm. New upper and lower estimates for these b ounds are presented and recast in terms of a collection of linear programmi ng problems. These estimates improve upon previously proposed linear progra mming bounds. The estimates are applied to derive exact bounds or provably close to exact bounds for several Viterbi detectors corresponding to coded and uncoded partial-response channels of practical interest in digital magn etic and optical recording.