Noise-predictive maximum-likelihood method combined with infinite impulse response equalization

An infinite impulse response (IIR) can closely approximate the high density magnetic recording channel response with only a single pole and a small number of zeros. As a consequence, a near-optimal performance can be achieved with the Viterbi algorithm (VA) incorporating a single-tap noise predictor. The number of states in the VA trellis is determined by the number of zeros used in the IIR modeling of the channel response. The single noise-predictor tap corresponds to the single pole in the IIR model. The overall complexity for a given level of performance is smaller with this approach than with the noise-predictive maximum-likelihood (NPML) method based on conventional partial response equalization.