Disclosed herein is an apparatus and method of calibrating the parameters
of a Viterbi detector 138 in which each branch metric is calculated based
on noise statistics that depend on the signal hypothesis corresponding to the branch.
An offline algorithm for calculating the parameters of data-dependent noise predictive
filters 304A-D is presented which has two phases: a noise statistics estimation
or training phase, and a filter calculation phase. During the training phase, products
of pairs of noise samples are accumulated in order to estimate the noise correlations.
Further, the results of the training phase are used to estimate how wide (in bits)
the noise correlation accumulation registers need to be. The taps [t2[k],
t1[k], t0[k]]
of each FIR filter are calculated based on estimates of the entries of a 3-by-3
conditional noise correlation matrix C[k] defined by
