• Journal of the Korean Institute of Telematics and Electronics B
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• v.32B no.12
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• pp.1565-1571
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• 1995

Misalignment of recording head position results in inter-track interference (ITI), which is a primary factor limiting radial(track) density in current digital magnetic channels. This paper proposes a multi- channel adaptive PRML for digital high-density recording channels, and compares it with the conventional single-channel PRML in the presence of ITI for the per- formance evaluation. Simulation results show that the proposed method removes ITI effectively when heal-misalignment occurs, then improving its performance significantly as compared with the single- channel PRML. As a result, it is confirmed that multi-channel adaptive PRML is well suited for high-density recording in digital magnetic channels.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.3
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• pp.133-141
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• 1996

As the recording density of digital magnetic recording channels increased, the nonlinear distortion caused by inadequate rise-times, demagnetizing field, and overwrite effect during the recording process becomes significant, resulting in limitation on the recording rate. In this paper, a new method for identifying the nonlinear distortion in hihg-density magnetic recording channel using and i.i.d. (independent, identically distributed) inut is described. The proposed method does not require the operatin of large-size matrix inversion which are necessary for the conventional method, and it enables us to estimate nonlinear parameters transition shifts, which can be used to compensate the nonlinear distortion, is demonstrated by computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.10
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• pp.821-826
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• 2012

Two-dimensional magnetic recording (TDMR) is treated as the next generation magnetic recording method, but because of its high channel bit error rate, it is difficult to use in practices. In this paper, we introduce a new writing method that can decrease the nonlinear media error effectively, and it can also achieve 10 Tb/$in^2$ of user bit density on a magnetic recording medium with 20 Teragrains/$in^2$.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.891-892
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• 2008

본 논문에서는 최근 주목받고 있는 에러 정정 기법 중 하나인 LDPC(Low Density Parity Check) 부호를 광 기록 채널(Optical Recording Channel)에 적용해 보았고 이때 사용되는 연판정 출력 알고리즘으로 MAP과 SOVA를 이용하여 성능을 비교하였다.

• Journal of IKEEE
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• v.15 no.1
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• pp.70-75
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• 2011

Longitudinal recording has been the cornerstone of all two generations of magnetic recording systems, FDD and HDD. In recent, perpendicular recording has received much attention as promising technology for future high-density recording system Research into signal processing techniques is paramount for the issued storage system and is indispensable like longitudinal recording systems. This paper focuses on the performance evaluation of the various detectors under perpendicular recording system. Parameters for improving the their performance are examined for some detectors. Detectors considered in this work are the partial response maximum likelihood (PRML), noise-predictive maximum likelihood (NPML), fixed delay tree search with decision feedback (FDTS/DF), dual decision feedback equalizer (DDFE) and multilevel decision feedback equalizer (MDFE). Their performances are analyzed in terms of mean squared error (MSE) and noise power spectra, and similarity between recording channel and partial response (PR) channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12C
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• pp.1177-1181
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• 2003

The modulation code with the limitation of consecutive transition length is a type of channel codes in high-density magnetic recording channel. When code sequence has two or less successive transitions, the detection performance of channel outputs can be improved. However, the code rate is reduced considerably. We present a rate 7/8 nut-length limited (RLL) code that consecutive transition length of each codeword is limited to 2 (j=2), and j is allowed to be 3 when codewords are connected. In addition, the consecutive zeros of the proposed code is limited to 7 (k=7).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10C
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• pp.758-763
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• 2008

We introduce a noise-predictive turbo equalization using noise filter in perpendicular magnetic recording(PMR) channel. The noise filter mitigates the colored noise in high-density PMR channel. In this paper, the channel detectors used are SOVA (Soft Output Viterbi Algorithm) and BCJR algorithm which proposed by Bahl et al., and the outer decoder used is LDPC (Low Density Parity Check) code that is implemented by sum-product algorithm. Two kinds of LDPC codes are experimented. One is the 0.5Kbyte (4336,4096) LDPC code with the code rate of 0.94, and the other is 1Kbyte (8432,8192) LDPC code with the code rate of 0.97.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.244-247
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• 2000

This paper deals with methods for partial response maximum-likelihood (PRML) detection and crosstalk cancellation. In accrodance with the demand for increased recording density, 20 gigabyte (Gbyte) digital versatile disk (DVD) ROM channel is considered. Channel is modelled to be close to real optical channel using DIFFRACT$\^$TM/. After comparing the spectral characteristics of various PR polynomials, P(D)=1＋D＋D$^2$＋D$^3$is proposed as a target PR. The performance of the system is illustrated under the condition that the readout signal is degraded by crosstalk, radial tilt and nonlinear distortions in optics. The experimental results show that crosstalk and nonlinear distortions degrade performance by about 2dB, respectively. We also show that when radial tilt is added to the crosstalk, the performance degradation assumes quite significant proprotions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.6
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• pp.1554-1566
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• 1996

In this paper, a new symbol timing algorithm for a magnetic recording system as HDD, is proposed. Above all, the Lorentzian channel model applied, the distortion and the attenuation problems of playback signals at high speed and storage density were considered. The structure and the operation of popular data detectors for HDD were understood, and the adopted symbol timing algorithm were profoundly analyzed. On the basis of these understanding and analysis, a new symbol timing algorithm for high density HDD was proposed, and the performance evaluation of this proposed algorithm was done.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6A
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• pp.562-567
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• 2002

Noise predictive maximum likelihood(NPML) detector embeds noise predictions/ whitening process in branch metric calculation of Viterbi detector and improves the reliability of branch metric computation. Therefore, PRML detector with a noise predictor achieves some performance improvement and has an advantage of low complexity. This paper shows that NP(1221)ML system through noise predictive PR-equalized signal has less complexity and better performance than high order PR(12321)ML system in high density perpendicular magnetic recording. The simulation results are evaluated using (1) random sequence and (2) run length limited (1,7) sequence, and they are applied to linear channel and nonlinear channel with normalized linear density $1.0{\leq}K_p{\leq}3.0$.