• Journal of KIISE:Computer Systems and Theory
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• v.28 no.8
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• pp.390-398
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• 2001

인터넷을 이용한 서비스와 산업이 급속도로 발전하면서 인터넷 서비스를 위한 효율적이며 확장성이 있는 고가용성 시스템이 매우 중요한 요소로 인식되고 있다. 인터넷 서비스를 위한 고가용성 시스템은 컴퓨터들이 쉬지 않고 서비스를 제공할 수 있는 active-active 형태로 구성되어야 하며, 확장성을 위해서 N개의 컴퓨터가 연결되어 클러스터를 구성하는 N-way 방식을 지원하여야 한다. 본 논문에서는 N개의 컴퓨터들이 클러스터로 연결된 N-way에서 active-active 형태의 구성을 위한 알고리즘을 제시하고, 이를 바탕으로 구현된 고가용성 시스템인 Diehard를 소개한다. Diehard는 인터넷 서비스의 특성을 고려해서 소프트웨어 SPOF를 모니터링하고, 부분적인 서비스 중단에 대한 다양한 복구 정책 등을 지원하도록 설계 및 구현되었다.

• Journal of KIISE:Computer Systems and Theory
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• v.30 no.9
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• pp.445-453
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• 2003

As cluster systems used for high performance computing consist of large number of running servers, one has to solve the low availability problems occurred by the high chance of the server failures. To handle the problems, it is necessary to have the precise definition of available performance of cluster systems that represents availability and performability of the systems simultaneously. Previous research results that mention availability issues lack for concerning system performance such as waiting time and response time in their availability definition. In this paper, we propose a new availability metric for (n, k)-way cluster systems which compose of n primary servers and k backup servers. With the metric, the change of system performance according to arrival rates is captured and the waiting time of a request can be kept below to a certain level. Using various system operating parameters, we calculate availability and downtime of cluster systems along with waiting tine deadline.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.123-126
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• 1995

Characteristics of control system design using Universal Learning Network (U.L.N.) are that a system to be controlled and a controller are both constructed by U.L.N. and that the controller is best tuned through learning. U.L.N has the same generalization ability as N.N.. So the controller constructed by U.L.N. is able to control the system in a favorable way under the condition different from the condition of the control system in learning stage. But stability can not be realized sufficiently. In this paper, we propose a robust control method using U.L.N. and second order derivatives of U.L.N.. The proposed method can realize better performance and robustness than the commonly used Neural Network. Robust control considered here is defined as follows. Even though initial values of node outputs change from those in learning, the control system is able to reduce its influence to other node outputs and can control the system in a preferable way as in the case of no variation. In order to realize such robust control, a new term concerning the variation is added to a usual criterion function. And parameter variables are adjusted so as to minimize the above mentioned criterion function using the second order derivatives of criterion function with respect to the parameters. Finally it is shown that the controller constricted by the proposed method works in an effective way through a simulation study of a nonlinear crane system.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.168-171
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• 2010

본 논문에서는 GaN HEMT 소자를 이용한 고출력 고효율 특성을 가지는 광대역 SSPA의 개발을 다루고 있다. 개발한 SSPA는 8W 급과 15W 급의 GaN HEMT 소자를 사용하여 Pre-Drive 증폭단을 구성하였으며, Drive 증폭단은 50W/150W급 GaN HEMT 소자를 직/병렬구조로 사용하였다. Main 증폭단은 4-way 분배기와 결합기를 이용한 Balanced Structure를 적용하여 높은 출력을 구현하였으며, 안정적인 동작을 위하여 음(-)전원 제어 회로와 출력신호 검출 회로를 포함하고 있다. 제작된 SSPA의 사용가능 대역은 2.9GHz~3.3GHz로 단일전원을 사용하고 있으며 100us 펄스 폭, 10% Duty Cycle 조건에서 60dB의 전압이득, 1kW 출력과 약 28% 효율 특성을 가지는 것으로 측정되었다. 본 논문에서 개발한 SSPA는 S-대역을 사용하는 레이더시스템의 송신단에 적용될 수 있다.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1993.06a
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• pp.869-872
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• 1993

The chaotic fuzzy logic systems behave in a more complex way than crisp chaotic systems, and they can show some advantages in complex applications. Such an application is introduced in this paper, namely in scrambling and ciphering the signals.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.693-697
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• 2008

Generally, the rate of reuse should be increased within the certain area for efficient operation of radio resources in a CDMA mobile communication system, and then signal interference between the sane radio channels should be minimized. for this reason, this study conducted a simulation of cell secterization methods(3 and 4 sectors) as a practical and immediately applicable method to the field to minimize signal interference, to construct an economical network, and to increase the efficiency of frequency use. Also, by analyzing RSSi, $E_c/I_o$, $E_b/N_t$ and 3-way handoff which were simulation results, their possibility of use was identified.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.1
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• pp.137-143
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• 2014

Smart education in the information window, type talent in modern society is changing as talented smart shoes, smart automation creative talent through education, training can be called education revolution. In other words, the advent of smart devices, such as knowledge and information and to actively growing individual customized training paradigm change in the way education and training to reflect this approach. Therefore, in this paper, a smart learning environment based technologies for implementing the system was designed to be the next generation of cloud computing and N screen-based smart education system was studied. From this, educational functions and features in a smart media environment, based on the analysis of the utilization of a smart education system, which maximizes the system design were studied.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.2017-2022
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• 2004

Data association is a process that matches a recent observation with known data set, which is used for the localization of mobile robots. Edges in topological maps have rich information which can be used for the data association. However, no systematic approach on using the edge data for data association has been reported. This paper proposes a systematic way of utilizing the edge data for data association. First, we explain a Local Generalized Voronoi Angle(LGA) to represent the edge data in 1-dimension. Second, we suggest a key factor extraction procedure from the LGA to reduce the number by $2^7-2^8$ times, for computational efficiency using the wavelet transformation. Finally we propose a way of data association using the key factors of the LGA. Simulations show that the proposed data association algorithm yields higher probability for similar edges in computationally efficient manner.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.12
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• pp.2828-2835
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• 2015

In this paper, we analyse the effect of redundancy types and non-stop forwarding scheme on network service availability. We use stochastic reward net models as enabling modeling approach for the analytical evaluation. We first design stochastic reward nets for redundancy models with or without non-stop forwarding and then evaluate their availability using Stochastic Petri Net Package.

• Journal of the Korean Operations Research and Management Science Society
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• v.28 no.1
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• pp.37-49
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• 2003

Using the concept of closed queueing network, we present a consistent way of interpreting existing duality relations among queueing systems. Also, using embedded Markov chains, we present a few new duality relations for the queueing systems with negative customers.