• 한국통신학회논문지
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• 제19권10호
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• pp.1945-1956
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• 1994

본 논문에서는 기존의 통신망을 통합하여 고속 멀티미디어 통신이 가능하도록 하는 다중 액세스망 프로토콜을 제시하였다. 향후 구축될 광대역 종합통신망과의 접속을 위해서는 새로운 구조 및 형식에 대한 정의가 필요하며, 이를 위해 기존의 고속링 프로토콜인 ATMR 및 MetaRing에 대해 알아보고, 그 기본 구성의 문제점을 분석하여 새로운 액세스 매커니즘을 제안하였다. ATMR은 윈도우 크기를 재설정하기 위한 리셋시간이 요구되므로 채널효율이 떨어지며, MetaRing의 경우에는 채널의 효율은 증가되지만 파라미터가 고정되어 있어 트래픽의 변화에 따라 성능이 크게 좌우된다. 이에 반해 제안된 프로토콜은 트래픽의 변화에 따라 파라미터를 능동적으로 변화시킴으로서 최적의 상태로 트래픽 제어가 가능하게 되며, 우선순위 기법을 적용하여 동기 및 비동기 트래픽의 통합 제어가 가능하도록 하였다. 본 메카니즘은 기존망의 통합 및 ATM 망을 구성하는 괴도단계의 시범방 구성에 응용될 수 있을 것으로 기대된다.

• 한국통신학회논문지
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• 제30권4C호
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• pp.200-206
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• 2005

적응 전송 기법은 변조방식, 부호율, 전력 등의 전송 매개변수를 채널의 상태에 적응시켜 무선 통신시스템의 성능을 향상시키는 기법이다. OFDM (Orthogonal frequency division multiplexing) 시스템에서는 이러한 적응기법을 부반송파별로 적용시킬 수 있다. 이 논문에서는 각 부채널의 상태에 따라 부반송파에 최적의 부호율을 적응시키는 적응부호율 OFDM 시스템을 고려한다. 성능 분석을 통해 적응부호율 OFDM 시스템이 비트오류율 $10^{-6}$에서 고정부호율 OFDM 시스템에 비해 $3\sim6$ dB의 신호 대 잡음비 이득 또는 $30\sim50\%$의 데이터 전송률 증가를 얻을 수 있음을 보인다.

• 한국컴퓨터정보학회논문지
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• 제22권9호
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• pp.57-64
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• 2017

CCSDS Standard is widely used in the international space telecommunication area. But standard recommendation of CCSDS is not restrictive, so, we can select an appropriate encryption protocol among the layer. For synchronization, encryption sync is attached in the beginning of the encrypted data. In the exceptional environmental condition, although the receiver can not decrypt the normal data, the sender have no conception of that situation. In this paper, we propose a two-stage SES alarmed link encryption synchronization method having optimized threshold value necessary to decide whether the receiver has a correct decryption or not. first, through the experiment of mutual relations between error rate and encryption synchronization detection error, we can predict worst communication environment for the selected encryption synchronization pattern. second, through the experiment for finding what number of consecutive frame synchronization error is an appropriate reference value and analysis of that experiment, we suggest an optimized threshold value for resynchronization request. lastly, through the output images we can predict the probability error that should be guaranteed by channel coder.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.366-366
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• 2016

Nanoscale observation of attachment systems of animals has revealed various exquisite multiscale architectures for essential functions such as gecko's locomotion, beetles' wing fixation, octopuses' sucking and crawling. In particular, the hierarchical 3-dimensional hexanonal nano-architectures in the tree frog's adhesion is known to have the capability of the enhancement of adhesion forces on the wet or rough surfaces due to the conformal contacts against rough surfaces and water-drainable micro channels. Here, we report that tree frog-inspired patches using unique artificial 3-dimensional hexagonal structures can be exploited to form reversibly enhanced adhesion against various highly curved and rough surfaces in dry and wet condition. To investigate the adhesion effect of micro-channels, we changed the arrangement of microstructure and spacing gaps between micro-channels. In addition, we introduced the 3-dimensional hexagonal hierarchical architectures to artificial patches to enhance to conformal contacts on the various rough surfaces such as skin and organs. Using the robust adhesion properties, we demonstrated the self-drainable and comfortable skin-attachable devices which can measure EKG (electrokardiogramme) for in-vitro diagnostics. As a result, bio-inspired programmable nano-architectures can be applied in versatile devices such as, medical patches, skin-attachable electronics etc., which would shed light on future smart, directional and reversible adhesion systems.

• ETRI Journal
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• 제37권1호
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• pp.66-76
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• 2015

In this work, we propose an efficient selective retransmission method for multiple-input and multiple-output (MIMO) wireless systems under orthogonal frequency-division multiplexing (OFDM) signaling. A typical received OFDM frame may have some symbols in error, which results in a retransmission of the entire frame. Such a retransmission is often unnecessary, and to avoid this, we propose a method to selectively retransmit symbols that correspond to poor-quality subcarriers. We use the condition numbers of the subcarrier channel matrices of the MIMO-OFDM system as a quality measure. The proposed scheme is embedded in the modulation layer and is independent of conventional hybrid automatic repeat request (HARQ) methods. The receiver integrates the original OFDM and the punctured retransmitted OFDM signals for more reliable detection. The targeted retransmission results in fewer negative acknowledgements from conventional HARQ algorithms, which results in increasing bandwidth and power efficiency. We investigate the efficacy of the proposed method for optimal and suboptimal receivers. The simulation results demonstrate the efficacy of the proposed method on throughput for MIMO-OFDM systems.

• 한국정보전자통신기술학회논문지
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• 제2권1호
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• pp.59-64
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• 2009

본 논문은 다중 안테나를 사용하는 통신시스템의 수신부에서 사용하는 복잡도가 낮은 신호검출기법을 제안한. 선형검출기법에는 Zero-Forcing (ZF)기법과 minimum mean squared error (MMSE) 기법이 있고, ZF기법은 MMSE 기법에 비해 하드웨어 구현관점에서 더 간단하나 성능이 열등한 것으로 알려져 있다. 일반적으로 통신시스템에서는 채널상황에 따라 modulation coding scheme (MCS)을 적응으로 바꾸어 사용한다. 본 논문에서는 사용되는 MCS 레벨에 따라 ZF기법과 MMSE기법 중 더 적합한 방식을 선택할 필요가 있음을 보인다. 또한 하드웨어 구현을 통해 적응 선형수신기의 복잡도가 기존의 MMSE 기법의 복잡도와 유사함을 보인다.

• BMB Reports
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• 제29권3호
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• pp.200-204
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• 1996

Nerve growth factor (NGF) is literally known to promote neural differentiation and survival in several peripheral and central neurons. Thus, it is Widely believed that NGF may serve as a therapeutic agent for many types of neuronal diseases. One of the mechanisms suggested to explain the protective role of NGF is that the trophic factor can prevent the increase of intracellular calcium ions which might be responsible for neural death. To examine whether or not the calcium hypothesis works even under pathological conditions, we applied NGF to cultures deprived of glucose. Surprisingly, what was observed here is that NGF rather promoted cell death under a glucose-deprived condition. What we call the NGF paradox phenomenon occurred in a calcium concentration-dependent manner, indirectly suggesting that NGF might increase intracellular calcium ions in cells deprived of glucose. This suggestion is further supported by the fact that nifedipine, a well-known L-type calcium channel blocker, could block the cell death potentiated by NGF. Here it is still premature to propose the complete mechanism underlying the NGF paradox phenomenon. However, this study certainly indicates that NGF as a therapeutic agent for neuronal diseases should be carefully considered before use.

• 대한기계학회논문집B
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• 제23권8호
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• pp.978-986
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• 1999

In this study, the general thermal and flow characteristics of flat tube with micro-channels has been studied and the correlation of Nusselt number and friction factor is proposed. The optimal flat tube geometry is determined by optimal design process. It is assumed to be a three dimensional laminar flow in the analysis of thermal and flow characteristics. The periodic boundary condition is applied since the geometry of flat tube with micro-channels shows uniform cross-section in primary flow direction. Local Nusselt number is examined for thermal characteristics of each membrane, and module average Nusselt number and friction factor are calculated to determine the characteristics of the heat transfer and pressure drop in overall flat tube with microchannels. The correlations between Nusselt number and friction factor are given by Reynolds number, aspect ratio of membranes, and the width of flat tube. ALM (Augmented Lagrangian Multiplier) method is applied to the correlations to determine an optimal shape of flat tube. It is shown that the optimal aspect ratio of flat tube is approximately 1.0, irrespective of the width of flat tube and Reynolds number.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.321-325
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• 2005

Bipolar plate is the main part with MEA in automotive PEMFC. It must have a good electrical conductivity and excellent corrosion resistance, be cost effective. Therefore, stainless steels have been studied by many researchers because of its corrosion resistance and cost benefits. But their properties are not sufficient for the application to bipolar plate for automotive PEMFC. In this work, we have performed stamping using various commercial stainless steels to select candidate material for biploar plate and to derive design parameters for stamping simulation. The results showed that a small curvature at the corner of flow field is more favorable due to easier a plastic deformation. Stamping process was simulated by changing surface condition, and the size and angle of channel. The optimum shape and spring back phenomena were evaluated. Surface coating was applied to increase the corrosion resistance and electrical conductivity of stainless steel. The electrical interfacial resistance was 10 to $15m{\Omega}cm^2$ under clamping force of 150psi. But corrosion resistance of coating on the stainless steel was not good due to the unstableness of microstructure.

• 한국수자원학회논문집
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• 제30권6호
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• pp.761-768
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• 1997

열발전소에서 비상 가동중단으로 냉각수 배수계통에 발생하는 비압축성 부정류를 해석하는 수치모형이 개발되었다. 개발된 수치모형은 냉각수 기계내부계통, 폐정, 공기실, 관로, 맨홀, 개수로 및 바다 등에 의한 복잡한 흐름에 대해 전체적인 부정류거동을 동시에 해석할 수 있는 기능을 가진다. 수치해법으로는 leap-forg 유한차분법을 적용하였으며, 간단한 경우에 대한 모형의 검증과 함께, 종래 배수암거 하류단에 적용되덕 고정수위경계조건에 대한 검토가 이루어졌다.