2,761 research outputs found
An RLL code design that maximises channel utilisation
Comprehensive (d,k) sequences study is presented, complemented with the design of a new, efficient, Run-Length Limited (RLL) code. The new code belongs to group of constrained coding schemas with a coding rate of R = 2/5 and with the minimum run length between two successive transitions equal to 4. Presented RLL (4, oo) code uses channel capacity highly efficiently, with 98.7% and consequently it achieves a high-density rate of DR = 2.0. It is implying that two bits can be recorded, or transmitted with one transition. Coding techniques based on the presented constraints and the selected coding rate have better efficiency than many other currently used codes for high density optical recording and transmission
A general construction of constrained parity-check codes for optical recording
This paper proposes a general and systematic code design method to efficiently combine constrained codes with parity-check (PC) codes for optical recording. The proposed constrained PC code includes two component codes: the normal constrained (NC) code and the parity-related constrained (PRC) code. They are designed based on the same finite state machine (FSM). The rates of the designed codes are only a few tenths below the theoretical maximum. The PC constraint is defined by the generator matrix (or generator polynomial) of a linear binary PC code, which can detect any type of dominant error events or error event combinations of the system. Error propagation due to parity bits is avoided, since both component codes are protected by PCs. Two approaches are proposed to design the code in the non-return-to-zero-inverse (NRZI) format and the non-return-to-zero (NRZ) format, respectively. Designing the codes in NRZ format may reduce the number of parity bits required for error detection and simplify post-processing for error correction. Examples of several newly designed codes are illustrated. Simulation results with the Blu-Ray disc (BD) systems show that the new d = 1 constrained 4-bit PC code significantly outperforms the rate 2/3 code without parity, at both nominal density and high density
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
REAL TIME MICROPROCESSOR TECHNIQUES FOR A DIGITAL MULTITRACK TAPE RECORDER
Transport properties of a standard compact - cassette tape
system are measured and software techniques devised to configure
a low - cost,direct digital recording system.
Tape - velocity variation is typically ยฑ 10% of standard speed
over tape lengths of 5 ยตm.with occasional variations of ยฑ40%.
Static tape - skew can result due to axial movement of the tape
reel when it spools.Dynamic tape skew occurs and is primarily
caused by tape - edge curvature with a constant contribution
due to the transport mechanism.Spectral skew components range
from 0.32 Hz to 8 Hz with magnitude normally within one 10 kbit/
sec- bit cell.The pinch roller works against the friction of the
tape guides to cause tape deformation.Average values of tape
deformation are 0.67 ยตm,0.85 ยตm and 1.08 ยตm for C60,C90 and
C120 tape respectively.
Parallel,software encoding / decoding algorithms have been
developed for several channel codes.Adaptive software methods
permit track data rates up to 3.33 k bits/sec in a rnultitrack
system using a simple microcomputer.For a 4 - track system,raw
error rates vary from 10หโท at 500 bits/sec/track to 10หโต at 3.33
kbits/sec/track.Adaptive software reduces skew - induced errors
by 50%.A skew - correction technique has been developed and
implemented on an 8 - track system at a track data rate of 10 k
bits/sec.
Real - time error correction gives a theoretical corrected
error rate of 10หยนยนfor a raw error rate of 10หโท. Multiple track
errors can cause mis - correction and interleaving is advised.
Software algorithms have been devised for Reed - Solomon code.
With a more powerful microprocessor this code m ay be combined
with the above techniques in a layered error-correction scheme.
The software techniques developed may be applied to N tracks
with an N - bit computer.Recording density may be increased by
using thin - film,multitrack heads and a faster computer.British Broadcasting Corporatio
CROSSTALK-RESILIANT CODING FOR HIGH DENSITY DIGITAL RECORDING
Increasing the track density in magnetic systems is very difficult due to inter-track interference
(ITI) caused by the magnetic field of adjacent tracks. This work presents a
two-track partial response class 4 magnetic channel with linear and symmetrical ITI; and
explores modulation codes, signal processing methods and error correction codes in order
to mitigate the effects of ITI.
Recording codes were investigated, and a new class of two-dimensional run-length
limited recording codes is described. The new class of codes controls the type of ITI
and has been found to be about 10% more resilient to ITI compared to conventional
run-length limited codes. A new adaptive trellis has also been described that adaptively
solves for the effect of ITI. This has been found to give gains up to 5dB in signal to noise
ratio (SNR) at 40% ITI. It was also found that the new class of codes were about 10%
more resilient to ITI compared to conventional recording codes when decoded with the
new trellis.
Error correction coding methods were applied, and the use of Low Density Parity
Check (LDPC) codes was investigated. It was found that at high SNR, conventional
codes could perform as well as the new modulation codes in a combined modulation and
error correction coding scheme. Results suggest that high rate LDPC codes can mitigate
the effect of ITI, however the decoders have convergence problems beyond 30% ITI
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