Partial response class I signaling applied to high density magnetic recording

For high density magnetic recording systems, equalizing to partial response signals of the form (1-D)(1+D)ⁿ and applying modulation codes with spectral nulls at DC and the Nyquist frequency have been proposed in Karabed and Siegel (1991). The present authors consider using the same DC/Nyquist-free codes, but equalizing to class I partial response signals with polynomial, (1+D). They find that when the received signal is detected by a Viterbi detector based upon a trellis that combines the equalized channel with the modulation constraint, the simpler detector for class I performs comparably to class IV, (1-D² ), or extended class IV (1+D-D²-D³) detectors