• 한국통신학회논문지
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• 제31권9B호
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• pp.792-802
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• 2006

In this paper, we propose an energy-efficient proactive data dissemination protocol with relatively low delay to cope well with highly mobile sink environments in sensor networks. In order for a dissemination tree to continuously pursue a dynamic sink, we exploit two novel algorithms: forward sink advertisement and distributed fast recovery. In our protocol, the tree is shared with the other slave sinks so that we call it Dynamic Shared Tree (DST) protocol. DST can conserve considerable amount of energy despite maintaining robust connection from all sources to sinks, since tree maintenance of DST is accomplished by just distributed local exchanges. In addition, since the DST is a kindof sink-oriented tree, each source on the DST disseminates data with lower delay along the tree and it also facilitates in-network processing. Through simulations, it is shown that the presented DST is considerably energy-efficient, robust protocol with low delay compared to Directed Diffusion, TTDD, and SEAD, in highly mobile sink environment.

• 한국통신학회논문지
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• 제41권1호
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• pp.1-11
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• 2016

본 논문에서는 Orthogonal Frequency Division Multiplexing(OFDM) 시스템에서 압축센싱을 이용하는 채널추정기법을 연구한다. 압축센싱은 측정벡터의 크기가 성능에 영향을 주는데, OFDM에서는 channel delay spread가 큰 경우에 압축센싱 기법을 사용하는데 제약이 된다. 본 논문에서는 채널추정 오차를 줄이기 위해서 OFDM data block에 pilot information을 추가해 측정벡터의 길이를 증가시켜 성능을 향상시킨다. 제안하는 방식이 성긴 신호의 위치를 찾을 확률을 높이고 압축센싱의 신호 복원 성능을 높인다. 모의실험을 통해 제안하는 방식이 기존 방식보다 신호 복원 능력이 더 우수함을 확인한다.

• Journal of Information Processing Systems
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• 제10권2호
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• pp.176-192
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• 2014

The realization of Wireless Multimedia Sensor Networks (WMSNs) has been fostered by the availability of low cost and low power CMOS devices. However, the transmission of bulk video data requires adequate bandwidth, which cannot be promised by single path communication on an intrinsically low resourced sensor network. Moreover, the distortion or artifacts in the video data and the adherence to delay threshold adds to the challenge. In this paper, we propose a two stage Quality of Service (QoS) guaranteeing scheme called Prioritized Multipath WMSN (PMW) for transmitting H.264 encoded video. Multipath selection based on QoS metrics is done in the first stage, while the second stage further prioritizes the paths for sending H.264 encoded video frames on the best available path. PMW uses two composite metrics that are comprised of hop-count, path energy, BER, and end-to-end delay. A color-coded assisted network maintenance and failure recovery scheme has also been proposed using (a) smart greedy mode, (b) walking back mode, and (c) path switchover. Moreover, feedback controlled adaptive video encoding can smartly tune the encoding parameters based on the perceived video quality. Computer simulation using OPNET validates that the proposed scheme significantly outperforms the conventional approaches on human eye perception and delay.

• ETRI Journal
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• 제27권1호
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• pp.1-12
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• 2005

We propose a heuristic buffer management scheme that uses both positive and negative acknowledgments to provide scalability and reliability. Under our scheme, most receiver nodes only send negative acknowledgments to their repair nodes to request packet retransmissions while some representative nodes also send positive acknowledgments to indicate which packets can be discarded from the repair node's buffer. Our scheme provides scalability because it significantly reduces the number of feedbacks sent by the receiver nodes. In addition, it provides fast recovery of transmission errors since the packets requested from the receiver nodes are almost always available in their buffers. Our scheme also reduces the number of additional retransmissions from the original sender node or upstream repair nodes. These features satisfy the original goal of treebased protocols since most packet retransmissions are performed within a local group.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권6호
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• pp.615-628
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• 2015

CGRA (Coarse-Grained Reconfigurable Architecture) based multi-core architecture can be considered as a suitable solution for the fault-tolerant computing. However, there have been a few research projects based on fault-tolerant CGRA without exploiting the strengths of CGRA as well as their works are limited to single CGRA. Therefore, in this paper, we propose two approaches to enable exploiting the inherent redundancy and reconfigurability of the multi-CGRA for fault-recovery. One is a resilient inter-CGRA fabric that is ring-based sharing fabric (RSF) with minimal interconnection overhead. Another is a novel intra/inter-CGRA reconfiguration technique on RSF for maximizing utilization of the resources when faults occur. Experimental results show that the proposed approaches achieve up to 94% faulty recoverability with reducing area/delay/power by up to 15%/28.6%/31% when compared with completely connected fabric (CCF).

• 한국광학회지
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• 제4권3호
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• pp.347-353
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• 1993

펌프-촉침 방법을 이용한 피코초 순간 흡광 속도분광기를 제작하고 피코초 순간 흡광 분광을 측정하는 다른 방법들과 비교하였다. 제작된 피코초 순간 흡광 속도분광기는 모드 록킹된 cw 색소 레이저에서 발생된 펌프 펄스와 촉침 펄스 사이의 지연시간 변화에 따른 시료의 순간 투과도를 잡금 증폭기를 사용하여 측정하였다. 이 속도분광기를 사용하여 측정된 순간 흡광 및 바닥 상태의 표백 재생 속도 곡선들을 보여주었다. 단일 파장에서 발광 또는 비발광 계의 순간 흡광 혹은 바닥 상태의 표백 재생의 아주 좋은 속도 곡선을 얻을 수 있었다.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2018년도 제58차 하계학술대회논문집 26권2호
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• pp.3-6
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• 2018

최근 방대한 양의 스트림 데이터가 생산되면서 이를 실시간으로 처리하기 위한 프레임워크가 등장하였으며, 오픈 소스 영역에서 Spark Streaming이 주목받고 있다. Spark Streaming은 분산 환경에서 성능 향상을 위해 지연 스케줄링을 기반으로 응용을 수행하지만, 장애 발생 시 사용 가능한 태스크 슬롯을 빠르게 할당받지 못할 경우 장애 복구 시간이 지연될 수 있다는 문제점이 있다. 이러한 문제점을 해결하기 위해 본 논문에서는 실행자의 태스크 슬롯 보장을 통해 대기 시간 없이 즉시 할당할 수 있도록 하는 개선 메커니즘을 제안하였고, 실험 결과 장애 복구 응답성이 39.14% 개선됨을 확인하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -3
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• pp.1948-1951
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• 2002

In this paper, we propose a chip timing recovery algorithm that is robust to frequency offset and time variant fading environments for DS/CDMA. The proposed structure is a modified non-coherent Delay Locked Loop (DLL) that employs a decimator. Analytical expression for the proposed non-coherent DLL S-curve and steady-state timing jitter is derived and confirmed by computer simulation. The results show that the proposed structure can reduce a steady-state timing jitter of the regenerated spreading code replica to frequency offset and time-variant fading in mobile radio channel, especially in very low SNR.

• 한국통신학회논문지
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• 제36권12A호
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• pp.1015-1023
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• 2011

In maritime communication, QoS problem caused by routing is very important. In this paper, we propose a method based on AOMDV protocol providing a route recovery mechanism when a link breaks in an active route to reduce lost packets. The results show that the proposed method can reduce packet loss ratio and delay time compared with the AOMDV.

• Clinical and Experimental Pediatrics
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• 제56권1호
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• pp.26-31
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• 2013

Purpose: Lymphocyte subset recovery is an important factor that determines the success of hematopoietic stem cell transplantation (HSCT). Temporal differences in the recovery of lymphocyte subsets and the factors influencing this recovery are important variables that affect a patient's posttransplant immune reconstitution, and therefore require investigation. Methods: The time taken to achieve lymphocyte subset recovery and the factors influencing this recovery were investigated in 59 children who had undergone HSCT at the Department of Pediatrics, The Catholic University of Korea Seoul St. Mary's Hospital, and who had an uneventful follow-up period of at least 1 year. Analyses were carried out at 3 and 12 months post-transplant. An additional study was performed 1 month post-transplant to evaluate natural killer (NK) cell recovery. The impact of pre- and post-transplant variables, including diagnosis of Epstein-Barr virus (EBV) DNAemia posttransplant, on lymphocyte recovery was evaluated. Results: The lymphocyte subsets recovered in the following order: NK cells, cytotoxic T cells, B cells, and helper T cells. At 1 month post-transplant, acute graft-versus-host disease was found to contribute significantly to the delay of $CD16^+/56^+$ cell recovery. Younger patients showed delayed recovery of both $CD3^+/CD8^+$ and $CD19^+$ cells. EBV DNAemia had a deleterious impact on the recovery of both $CD3^+$ and $CD3^+/CD4^+$ lymphocytes at 1 year post-transplant. Conclusion: In our pediatric allogeneic HSCT cohort, helper T cells were the last subset to recover. Younger age and EBV DNAemia had a negative impact on the post-transplant recovery of T cells and B cells.