Noise-predictive partial-response equalizers and applications

Receivers for partial-response systems typically use a linear partial-response (PR) equalizer which shapes the channel response to a desired one of acceptably short duration followed by a Viterbi detector. In this paper we consider zero-forcing and minimum mean-square error (MMSE) noisepredictive PR equalizers. In analogy to a noise-predictive decision-feedback equalizer (DFE), a noise-predictive PR equalizer consists of a linear equalizer which shapes the channel to a predetermined partial-response function followed by a predictor which whitens the noise and the residual distortion at the equalizer output. Assuming correct decisions and applying results from prediction theory, it is shown that the MMSE of a noise-predictive PR equalizer equals that of a DFE which employs no PR shaping. This result asserts that the performance of a receiver with a PR shaping equalizer can always be improved by attaching a noise-whitening predictor. Simulation results are presented for channels typically encountered in wire transmission and magnetic recording, i.e., channels with a spectral null at dc and strong high-frequency attenuation. The results show a substantial performance improvement when a noise-predictive PR equalizer is used.