Adaptive soft-output detector for magnetic tape read channels

A method, comprising:

• reading precoded data from a magnetic tape medium to produce a signal;
• passing the signal through a noise whitening filter, wherein the noise whitening filter is configured to control variance of noise affecting the signal output from the filter, wherein the noise whitening filter processes the signal according to the following transfer polynomial:
• W(D)=1−(p1D+ . . . +pλDλ), where p1 . . . pλ are the noise whitening coefficients with the noise whitening filter having 2λ states, and where the tape channel is characterized by a transfer polynomial F(D)=1+f1D+ . . . +fLDL where D is delay corresponding to bit duration, with the tape channel having 2L states, L represents a memory length of the tape channel, and λ represents a memory length of the noise whitening filter,
• passing the signal through a soft detector to calculate first soft information about each bit of the signal and to provide adaptive compensation for the precoded data;
• sending the first soft information to a soft decoder,
• passing the signal through the soft decoder to calculate second soft information about each bit of the signal;
• and
• sending the second soft information to the soft detector,
• wherein the precoded data comprises a characteristic of being passed through at least one precoder prior to being written to the magnetic tape medium.

A computer program product, comprising a computer readable storage medium having computer readable program code embodied therewith, the computer readable program code readable/executable by a processor to cause the processor to:

• receive, by the processor, a signal comprising precoded data read from a magnetic tape medium and pass the signal through a soft detector to calculate first soft information about each bit of the signal and to provide adaptive compensation for the precoded data;
• send, by the processor, the first soft information to a soft decoder;
• pass, by the processor, the signal through the soft decoder to calculate second soft information about each bit of the signal;
• and
• send, by the processor, the second soft information to the soft detector,
• wherein the precoded data comprises a characteristic of being passed through at least one precoder prior to being written to the magnetic tape medium, and
• wherein the characteristic of the precoded data is consistent with a precoder that applies 1/(1⊕D2) to bits of data bk, where D is delay corresponding to bit duration.