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Skew-Dependent Performance Evaluation of Array-Reader-Based Magnetic Recording With Dual-Reader
Euiseok Hwang,Oenning, Travis,Mathew, George,Rahgozar, Parviz,Tedja, Suharli,Han Fang,Garfunkel, Glen,Yan Wu,Hu, David,Duquette, Paul,Fitch, Ken,Rabbitt, Chad,Petrizzi, Joseph,Wilson, Bruce,Rauschmaye IEEE 2015 IEEE transactions on magnetics Vol.51 No.4
<P>Array-reader-based magnetic recording (ARMR) shows potential to achieve areal density capability (ADC) beyond 1 Tb/in<SUP>2</SUP> by jointly processing multiple readback streams. Dual-reader ARMR with two read sensors and associated read channel signal processing algorithms are currently being actively investigated. In this paper, dual-reader ARMR performance is evaluated focusing on skew-induced variation in cross-track separation (CTS) between the two read sensors. Spin-stand captured waveforms based evaluation is presented for the cases where a dual-reader with certain CTS and skew is emulated using captures from a single-reader at different cross-track locations as well as for the case of actual dual-reader-based captures, where the latter also accounts for head rotation. Based on bit error rate scan along cross-track under various squeezed recording and skew conditions, squeeze-to-death margin-based ADC gain of ARMR is predicted. Dual-reader ARMR shows 5%-10% ADC gain over single-reader for CTS less than 0.6 track pitch, while showing limited gains for larger CTS. Also presented is the performance evaluation of dual-reader ARMR on spin-stand using a hardware accelerated ARMR performance evaluation platform, called Stingray, which uses four Avago read channel silicon chips and a customized field programmable gate array to enable high-speed joint equalization and detection using dual-reader readback streams.</P>
Joint Equalization of Asynchronous Reads in Array-Reader-Based Interlaced Magnetic Recording
Hwang, Euiseok,Chang, Wu,Yoon, Seungwook IEEE 2019 IEEE transactions on magnetics Vol.55 No.3
<P>This paper proposes a joint read equalization scheme for interlaced magnetic recording (IMR) employing an array of readers, where multi-reader captured waveforms from asynchronously recorded tracks are jointly processed for single or multiple track data retrievals. In the array-reader-based IMR (ARIMR), the inter-track interference (ITI) collected from one reader is not necessarily synchronized to the other readers, especially in the case of a large cross-track separation (CTS) between the readers due to the linear density differentiation between the neighboring tracks. For the efficient mitigation of such asynchronous ITIs, an effective resampling-based joint equalization scheme is proposed in this paper, where multiple readbacks are digitally synchronized for designated target tracks, and joint processing of them suppresses the ITI in the equalized output. Furthermore, the proposed effective synchronization can be applied for joint multi-track retrievals when the CTS of the array reader is closed to the track pitch. For performance evaluations of the proposed joint read equalization scheme, numerical ARIMR channel simulations by the micro-pixelated magnetic channel model are conducted, and a bit error rate performance is evaluated under various configurations. In addition, waveforms captured from a dual-reader hard disk drive are evaluated with the proposed joint read equalization schemes for practical performance measurements of ARIMR. In both evaluations, unfavorable CTS conditions are investigated to account for the dominant skew effect in ARIMR, where the proposed joint equalization scheme enhances the off-track capability performance, especially with the customized configurations of interlaced recording. In overall, ARIMR with joint read equalization shows the potential of an areal density capability gain and a doubling of the data transfer rate over the conventional perpendicular magnetic recording and legacy IMR.</P>
Generalized Interlaced Magnetic Recording With Flexible Inter-Track Interference Cancellation
Hwang, Euiseok,Yoon, Seungwook IEEE 2018 IEEE transactions on magnetics Vol.54 No.11
<P>In this paper, interlaced magnetic recording (IMR) is generalized with a flexible inter-track interference cancellation (F-ITIC) scheme to enhance the overall areal density capability (ADC) by balancing and mitigating the mutual ITI between neighboring tracks. The IMR showed ADC gain by interlaced recording of aggressive bit density (BD) top and relaxed BD bottom tracks, where asynchronous ITI mitigation was applied to the bottom ones. On the other hand, IMR configuration can be generalized by the selective write width control, such that narrower relaxed BD top tracks are recorded over wider aggressive BD bottom tracks. In this generalized IMR (G-IMR), balanced ITI between interlaced tracks can provide ADC gain over legacy IMR (L-IMR) and customized F-ITIC for both tracks can further increase the gain. Note that the ITI processing scheme for G-IMR should be flexible in order to manage the ITI signals from high BD affecting low BD tracks, or vice versa. To evaluate the performance of G-IMR with the F-ITIC, numerical evaluations are conducted with the micro-pixelated magnetic channel model. The results show that G-IMR provides a favorable tradeoff between both tracks’ BDs and track density associated mutual ITIs, which offers a tangible ADC gain with the ITI cancellation over the L-IMR.</P>
공유셀을 가진 계층적 셀룰라 망에서 멀티트래픽을 위한 적응적인 호 수락 제어 기법
황의석(Euiseok Hwang),원정재(Jeongjae Won),이형우(Hyongwoo Lee),조충호(Choongho Cho) 한국정보과학회 1999 한국정보과학회 학술발표논문집 Vol.26 No.1A
계층적 마이크로 셀 환경에서 멀티미디어 서비스의 이동성 보장을 위한 핸드오프 문제를 공유셀을 이용하여 해결 할 수 있다. 본 연구에서는 이러한 공유셀을 이용하여 클러스터간 멀티미디어 트래픽의 핸드오프 호 수락 제어기법을 제안한다. 이를 위하여 멀티미디어 트래픽의 특성별로 각각 인접한 셀의 상태정보와 클러스터의 상태 정보를 이용한 분산 호 수락 제어 기법을 적용한다. 또한 공유셀에서의 호 수락 제어 파라미타 값에 따른 혼 손실율과 핸드오프 호 지체율동을 시뮬레이션하여 분석하였다.
Survival and Morbidities in Infants with Birth Weight Less than 500 g: a Nationwide Cohort Study
Hwang Ji Hye,Jung Euiseok,Lee Byong Sop,Kim Ellen Ai-Rhan,Kim Ki-Soo 대한의학회 2021 Journal of Korean medical science Vol.36 No.31
Background: This study aimed to investigate the survival and morbidities of infants in the Korean Neonatal Network (KNN) with birth weight (BW) < 500 g. Methods: The demographic and clinical data of 208 live-born infants with a BW < 500 g at a gestational age of ≥ 22 weeks who were treated in the neonatal intensive care units of the KNN between 2013 and 2017 were reviewed. Results: The survival rate of the infants was 28%, with a median gestational age and BW of 243/7 weeks (range, 220/7–336/7) and 440 g (range, 220–499), respectively. Multivariable Cox proportional hazards analysis demonstrated that survival to discharge was associated with longer gestation, higher BW, female sex, singleton gestation, use of any antenatal corticosteroids, and higher Apgar scores at 5 minutes. The overall survival rates were significantly different between the BW categories of < 400 g and 400–499 g. However, there was no significant difference in the incidence of any morbidity between the BW groups. Half of the deaths of infants with BW < 500 g occurred within a week of life, mainly due to cardiopulmonary and neurologic causes. The major causes of death in infants after 1 week of age were infection and gastrointestinal disease. Among the surviving infants, 79% had moderate to severe bronchopulmonary dysplasia, 21% underwent surgical ligation of patent ductus arteriosus, 12% had severe intraventricular hemorrhage (grade III–IV), 38% had sepsis, 9% had necrotizing enterocolitis (stage ≥ 2), and 47% underwent laser treatment for retinopathy of prematurity. The median length of hospital stay was 132 days (range, 69–291), and 53% required assistive devices at discharge. Conclusion: Despite recent advances in neonatal intensive care, the survival and morbidity rates of infants with BW < 500 g need further improvement.
IEEE 2018 IEEE transactions on magnetics Vol.54 No.9
<P>In this paper, an adaptive inter-track interference (ITI) mitigating scheme is proposed for interlaced magnetic recording (IMR) with random frequency offsets. Recently, proposed IMR has a potential areal density capability gain over conventional perpendicular magnetic recording, as it involves writing tracks with differentiated linear densities in an interlaced manner, while suppressing the ITI efficiently during the reading operation via asynchronous ITI cancellation (A-ITIC). The A-ITIC estimates and subtracts the ITI contributions from its side tracks in the effectively synchronized domain via interpolation-filter-based relative timing adjustments. However, when the tracks are recorded with non-negligible random frequency offsets, the ITI response is averaged out, providing a weak estimate, and the A-ITIC-based bit error rate performance gain disappears. In order to compensate for these dynamic timing misalignments, an adaptive ITI mitigation scheme is proposed called an adaptive A-ITIC, where the ITI response is continuously updated via effective timing adjustments along the sector. Numerical evaluations using a micro-pixel-based magnetic channel model show that the legacy A-ITIC performs poorly for IMR with non-negligible random frequency offsets, whereas the proposed adaptive scheme compensates for most of the performance degradation by effectively tracing the relative timing shifts via adaptation measures.</P>