josh@polaris.UUCP (Josh Knight) (02/25/86)
Reposted because of apparent network prolbems...
%A Arvind M. Patel
%T Adaptive Cross-Parity (AXP) Code for a High-Density Magnetic Tape System
%J IBM J R&D
%V 29
%N 6
%P 546-562
%D NOV 1985
%X This paper describes an error-correction system, called adaptive
cross-parity (AXP) code, for the IBM 3480, a new high-density 18-track
tape storage subsystem. Redundancy is applied to two interleaved sets
of nine tracks in the same proportion as that in the previous IBM 3420
tape machines. The coding structure, however, is simpler, for it avoids
the complex computations of Galois fields. The coding structure is
based on a concept of interactive vertical and cross-parity checks,
where the cross-parity checks span both sets of tracks and are used in
either set in an adaptive manner. As a result, the overall
error-correcting capability is substantially improved without increasing
the redundancy. Decoding, in which simple parity equations are
preprocessed, is designed to progress iteratively. By means of adaptive
use of redundancy, the new method corrects up to three known erroneous
tracks in any one set of nine tracks and up to four known erroneous
tracks in the two sets together. The code also identifies the first
unknown erroneous track in each of the two sets, and subsequently
identifies the second unknown erroneous track in one of the two sets
while providing correction for all these tracks. The result is
generalized for a system with any number of tracks divided into a
multiple number of unequal sets.
%A Richard C. Scheider
%T Write Equalization in High-Linear-Density Magnetic Recording
%J IBM J R&D
%V 29
%N 6
%P 563-568
%D NOV 1985
%X For many years, equalization has been used on the read side of a
magnetic-recording channel to obtain a desired signal shape at the
detector. Compensation on the write side has, for the most part, been
limited to moving transition locations to offset read-signal peak
shifts. This paper presents a new method of equalization on the write
side through the addition of pulses at strategic locations on the write
waveform. The resulting write current continues to be a two-level
signal, so ac bias is not required. A linear transfer function can be
derived for these write equalizers. This enables the recording-channel
designer to partition the equalization more optimally between the write
and read sides. The principal benefit of write equalization is that the
read-flux-amplitude differences between high and low densities are
significantly reduced. This permits maximum use of the linear operating
region of the magnetoresistive read head. By providing high-frequency
boosts on the write side, write equalization can reduce high-frequency
noise at the read detector. Test results of channel linearity, as well
as read signal waveshapes, are presented.
%A P. Carnevali
%A L. Coletti
%A S. Patarnello
%T Image Processing by Simulated Annealing
%J IBM J R&D
%V 29
%N 6
%P 569-579
%D NOV 1985
%X It is shown that simulated annealing, a statistical mechanics method
recently proposed as a tool in solving complex optimization problems,
can be used in problems arising in image processing. The problems
examined are the estimation of the parameters necessary to describe a
geometrical pattern corrupted by noise, the smoothing of bi-level images,
and the process of halftoning a continuous-level image. The analogy
between the system to be optimized and an equivalent physical system,
whose ground state is sought, is put forward by showing that some of
these problems are formally equivalent to ground state problems for
two-dimensional Ising spin systems. In the case of low signal-to-noise
ratios (particularly in image smoothing), the methods proposed here give
better results than those obtained with standard techniques.
%A R.J.S. Bates
%A L.A. Sauer
%T Jitter Accommodation in Token-Passing Ring LANs
%J IBM J R&D
%V 29
%N 6
%P 580-587
%D NOV 1985
%X In a token-passing ring Local Area Network (LAN) each message
accumulates phase jitter as it travels around the ring. Unlike typical
digital transmission systems, which tend to have random data traffic,
ring systems carrying computer-generated traffic may have long strings
of repetitive-pattern data. This traffic produces a jitter amplitude
which is a function of the message statistics and the transmission
characteristics of the physical layer. For the system to be stable,
this jitter must be controlled. This paper describes the
repetitive-pattern jitter generation and accumulation process and gives
a methodology for designing the physical layer components to accommodate
it.
%A Haruhio Matino
%T Analysis of the Holding Current in CMOS Latch-Up
%J IBM J R&D
%V 29
%N 6
%P 588-592
%D NOV 1985
%X The holding current in CMOS latch-up with or without well and/or
substrate bias has been examined. Measurements indicate that the
holding current increases significantly with reverse bias and low
shunting base resistance. It is shown that a previous equation for the
holding current is inaccurate, and a new equation for holding current
with bias is presented.
--
Josh Knight, IBM T.J. Watson Research
josh at YKTVMH on BITNET, josh.yktvmh@ibm-sj.arpa
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