33 research outputs found
An Optimal Unequal Error Protection LDPC Coded Recording System
For efficient modulation and error control coding, the deliberate flipping
approach imposes the run-length-limited(RLL) constraint by bit error before
recording. From the read side, a high coding rate limits the correcting
capability of RLL bit error. In this paper, we study the low-density
parity-check (LDPC) coding for RLL constrained recording system based on the
Unequal Error Protection (UEP) coding scheme design. The UEP capability of
irregular LDPC codes is used for recovering flipped bits. We provide an
allocation technique to limit the occurrence of flipped bits on the bit with
robust correction capability. In addition, we consider the signal labeling
design to decrease the number of nearest neighbors to enhance the robust bit.
We also apply the density evolution technique to the proposed system for
evaluating the code performances. In addition, we utilize the EXIT
characteristic to reveal the decoding behavior of the recommended code
distribution. Finally, the optimization approach for the best distribution is
proven by differential evolution for the proposed system.Comment: 20 pages, 18 figure
Enhanced coding, clock recovery and detection for a magnetic credit card
Merged with duplicate record 10026.1/2299 on 03.04.2017 by CS (TIS)This thesis describes the background, investigation and construction of a system
for storing data on the magnetic stripe of a standard three-inch plastic credit
in: inch card. Investigation shows that the information storage limit within a 3.375 in
by 0.11 in rectangle of the stripe is bounded to about 20 kBytes. Practical issues
limit the data storage to around 300 Bytes with a low raw error rate: a four-fold
density increase over the standard. Removal of the timing jitter (that is prob-'
ably caused by the magnetic medium particle size) would increase the limit to
1500 Bytes with no other system changes. This is enough capacity for either a
small digital passport photograph or a digitized signature: making it possible
to remove printed versions from the surface of the card.
To achieve even these modest gains has required the development of a new
variable rate code that is more resilient to timing errors than other codes in its
efficiency class. The tabulation of the effects of timing errors required the construction
of a new code metric and self-recovering decoders. In addition, a new
method of timing recovery, based on the signal 'snatches' has been invented to
increase the rapidity with which a Bayesian decoder can track the changing velocity
of a hand-swiped card. The timing recovery and Bayesian detector have
been integrated into one computation (software) unit that is self-contained and
can decode a general class of (d, k) constrained codes. Additionally, the unit has
a signal truncation mechanism to alleviate some of the effects of non-linear distortion
that are present when a magnetic card is read with a magneto-resistive
magnetic sensor that has been driven beyond its bias magnetization.
While the storage density is low and the total storage capacity is meagre in
comparison with contemporary storage devices, the high density card may still
have a niche role to play in society. Nevertheless, in the face of the Smart card its
long term outlook is uncertain. However, several areas of coding and detection
under short-duration extreme conditions have brought new decoding methods
to light. The scope of these methods is not limited just to the credit card
EQUALISATION TECHNIQUES FOR MULTI-LEVEL DIGITAL MAGNETIC RECORDING
A large amount of research has been put into areas of signal processing, medium design,
head and servo-mechanism design and coding for conventional longitudinal as well
as perpendicular magnetic recording. This work presents some further investigation in the
signal processing and coding aspects of longitudinal and perpendicular digital magnetic
recording.
The work presented in this thesis is based upon numerical analysis using various simulation
methods. The environment used for implementation of simulation models is C/C + +
programming. Important results based upon bit error rate calculations have been documented
in this thesis.
This work presents the new designed Asymmetric Decoder (AD) which is modified to
take into account the jitter noise and shows that it has better performance than classical
BCJR decoders with the use of Error Correction Codes (ECC). In this work, a new method
of designing Generalised Partial Response (GPR) target and its equaliser has been discussed
and implemented which is based on maximising the ratio of the minimum squared
euclidean distance of the PR target to the noise penalty introduced by the Partial Response
(PR) filter. The results show that the new designed GPR targets have consistently
better performance in comparison to various GPR targets previously published.
Two methods of equalisation including the industry's standard PR, and a novel Soft-Feedback-
Equalisation (SFE) have been discussed which are complimentary to each other.
The work on SFE, which is a novelty of this work, was derived from the problem of Inter
Symbol Interference (ISI) and noise colouration in PR equalisation. This work also shows
that multi-level SFE with MAP/BCJR feedback based magnetic recording with ECC has
similar performance when compared to high density binary PR based magnetic recording
with ECC, thus documenting the benefits of multi-level magnetic recording. It has been
shown that 4-level PR based magnetic recording with ECC at half the density of binary PR
based magnetic recording has similar performance and higher packing density by a factor
of 2.
A novel technique of combining SFE and PR equalisation to achieve best ISI cancellation
in a iterative fashion has been discussed. A consistent gain of 0.5 dB and more
is achieved when this technique is investigated with application of Maximum Transition
Run (MTR) codes. As the length of the PR target in PR equalisation increases, the gain
achieved using this novel technique consistently increases and reaches up to 1.2 dB in case
of EEPR4 target for a bit error rate of 10-5
An RLL-Constrained LDPC Coded Recording System Using Deliberate Flipping and Flipped-Bit Detection
International audienceIn this paper, a low-density parity-check (LDPC) coded recording system is investigated, for which the run-length-limited (RLL) constraint is satisfied by deliberate flipping at the write side and by estimating the flipped bits at the read side. Two approaches are proposed for enhancing the error performance of such a system. The first approach is to alleviate the negative effect of incorrect estimation of the flipped bits by adjusting the soft information. The second approach is to increase the likelihood of the correct detection of flipped bits by designing a flipped-bit detection algorithm that utilizes both the RLL constraint and the parity-check constraint of the LDPC code. These two approaches can be combined to obtain significant improvement in performance over previously proposed methods
Design and analysis of parity-check-code-based optical recording systems
Ph.DNUS-TU/E JOINT PH.D. PROGRAMM
Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)
Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial cellular communications services. While the first and second International Mobile Satellite Conferences (IMSC) mostly concentrated on technical advances, this Third IMSC also focuses on the increasing worldwide commercial activities in Mobile Satellite Services. Because of the large service areas provided by such systems, it is important to consider political and regulatory issues in addition to technical and user requirements issues. Topics covered include: the direct broadcast of audio programming from satellites; spacecraft technology; regulatory and policy considerations; advanced system concepts and analysis; propagation; and user requirements and applications
Third International Symposium on Space Mission Operations and Ground Data Systems, part 1
Under the theme of 'Opportunities in Ground Data Systems for High Efficiency Operations of Space Missions,' the SpaceOps '94 symposium included presentations of more than 150 technical papers spanning five topic areas: Mission Management, Operations, Data Management, System Development, and Systems Engineering. The papers focus on improvements in the efficiency, effectiveness, productivity, and quality of data acquisition, ground systems, and mission operations. New technology, techniques, methods, and human systems are discussed. Accomplishments are also reported in the application of information systems to improve data retrieval, reporting, and archiving; the management of human factors; the use of telescience and teleoperations; and the design and implementation of logistics support for mission operations