Adaptive noise-predictive maximum-likelihood (NPML) data detection for magnetic tape storage systems
by E. Eleftheriou,
S. Ölçer,
and R. A. Hutchins
Advanced data detection will be one of the key enablers to achieving
the very high areal recording densities of future tape storage systems.
Departing from the partial-response maximum-likelihood
(PRML)-based read channel design traditionally used in tape
systems, this paper describes noise-predictive maximum-likelihood
(NPML) detection, which is a technique that has been known for
many years in the hard-disk-drive industry but has been introduced
for the first time in the tape storage industry in IBM tape drives.
In the NPML read channel design, the readback signals are
conditioned prior to data detection so that their noise components
are statistically decorrelated and reduced in power. This paper
describes the basic principles of NPML detection and its application
to tape systems in the form of a 16-state detector. It is argued that,
because of the inherent variability of the recording channel
characteristics in tape drives, fully adaptive NPML detection needs to
be realized in order to optimize detection performance. Actual
readback waveforms of data recorded on metal particulate as well
as barium-ferrite particulate tape media are used to illustrate the
error rate performance achieved by 16-state and 32-state NPML
detectors. It is shown that, under realistic worst-case channel
conditions, a 16-state NPML detector could offer improvement in
error rate after an error-correcting code of approximately two
orders of magnitude.
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