MODIFIED VITERBI DETECTOR FOR JITTER NOISE DOMINANT CHANNELS

A Viterbi detector includes circuitry for receiving an NRZ encoded received signal in an EEPR4 channel to decode the signal according to &lgr;k(i)=(zk−yk(i))2−&agr;(i), wherein &agr;(i) is m &agr;, &agr; is a positive constant, m is a number of transitions within the most current four symbol periods, &lgr;k(i) is a branch metric at time k for an ith Viterbi branch, k is a time period, zk is a received value at time k, &lgr;k(i) is a metric used to determine a next state of the Viterbi based upon a maximum likelihood evaluation for an ith branch, ak, ak−1, ak−2, ak−3 are received state values at respective time periods k, k−1, k−2, and k−3, and yk is an ideal sample associated with an ith branch. The detector is operated to decode a received data value by determining whether the received value is in a space containing first (90) and second (92) possible decode values. The space has a boundary (96) substantially equidistant from the first (90) and second (92) possible decode values and separating the first and second possible decode values. If the received value is within a first portion of the space closest to the first decode value, the received value is decoded as the first decode value. If the received value is within a second portion of the space closest to the second decode value, it is decoded as the second decode value. A value (&agr;) that estimates an amount of jitter noise in a channel (26) through which the received value has passed is produced. The boundary (96) is then moved an additive amount (1&agr;, 2&agr;, 3&agr;) determined by the value that estimates an amount of jitter noise, wherein the boundary is moved (97, 98, 99) to enlarge whichever of the first and second spaces that contains a larger amount of jitter noise.