• Journal of the Korean Solar Energy Society
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• v.30 no.3
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• pp.25-32
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• 2010

A real-time monitoring system was developed for transfer, receive, backup and analysis of wind power data at three wind farm(Hang won, Hankyung and Sung san) in Jeju. For this monitoring system a communication system analysis, a collection of data and transmission module development, data base construction and data analysis and management module was developed, respectively. These modules deal with mechanical, electrical and environmental problem. Especially, time series graphic is supported by the data analysis and management module automatically. The time series graphic make easier to raw data analysis. Also, the real-time monitoring system is connected with wind power forecasting system through internet web for data transfer to wind power forecasting system's data base.

• The KIPS Transactions:PartC
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• v.10C no.5
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• pp.603-610
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• 2003

On the optical network, it is important to build restoration scheme capable to network survivability in preparation of potential failure on communication route. This paper analyze the existing schemes on restoration of failure on the optical network, and propose deferred commit scheme to improve resource utilization and management efficiency. Also, the transfer flow of messages needed for transferring restoration signal are presented in a concrete way and delay time required by shared mesh restoration scheme is explained in a substantial way. Simulation-based comparative analysis of various schemes is performed.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.874-876
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• 2005

임베디드 시스템에서의 캐시 메모리는 시스템의 성능에 큰 영향을 줄뿐만 아니라 전체 에너지 소비 중 $50\%$ 정도를 소비하고 있어 캐시 메모리의 성능과 에너지 소비는 큰 관심거리 중 하나다. 공정의 미세화로 캐시 메모리의 에너지 소비 중 누수 전류에 의한 에너지 소비의 비중이 더 커지고 있어, 정적 에너지 소비를 줄이기 위한 다양한 연구가 진행 중이다. 에너지 절약과 성능 향상은 손익 상쇄(Trade-off)관계에 있어 두 가지 목표를 동시에 달성하기는 힘들다. 본 논문에서는 성능 향상을 위하여 여러 가지 캐시 구조중 접속 속도가 가장 빠른 직접 사상 캐시를 사용하고, 완전 연관 캐시를 사용하여 직접 사상 캐시의 단정을 보완 할 수 있는 백업 캐시 시스템을 제안한다. 시스템 성능을 향상 시키면서 백업 캐시의 누수에너지를 절약하기 위해 직접 사상 캐시와 완전 연관 캐시를 서로 다른 한계 전압을 가지는 SRAM으로 구성한다. 직접 사상 캐시는 낮은 한계 전압의 SRAM로 구성하여 높은 성능을 내고, 완전 연관 캐시는 직접 사상 캐시에 비해 상대적으로 속도는 느리지만 누수 에너지가 적은 높은 한계 전압을 가지는 SRAM으로 구성하여 직접 사상 캐시를 보완하는 역할을 할 것이다.

• Journal of Positioning, Navigation, and Timing
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• v.2 no.1
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• pp.75-80
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• 2013

This article presents the design of long range navigation (LORAN)-disciplined oscillator (LDO), employing the timing information of the LORAN system, which was developed as a backup system that corrects the vulnerability of the global positioning system (GPS)-based timing information utilization. The LDO designed on the basis of hardware generates a timing source synchronized with reference to the timing information of the LORAN-C receiver. As for the LDO-based timing information measurement, the Kalman filter was applied to estimate the measurement of which variance was minimized so that the stability performance could be improved. The oven-controlled crystal oscillator (OCXO) was employed as the local oscillator of the LDO. The controller was operated by digital proportional-integral-derivative (PID) controlling method. The LDO performance evaluation environment that takes into account the additional secondary factor (ASF) of the LORAN signals allows for the relative ASF observation and data collection using the coordinated universal time (UTC). The collected observation data are used to analyze the effect of ASF on propagation delay. The LDO stability performance was presented by the results of the LDO frequency measurements from which the ASF was excluded.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.109-117
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• 2015

This paper proposes the comparison results of various optimal power flow algorithms (OPF) to calculate the locational marginal prices (LMP) of the unreduced full scale Korean transmission system. Five different types of optimal power flow models are employed: Full AC OPF, Cubic AC OPF, Quadratic AC OPF, Linear AC OPF and DC OPF. As the results, full AC OPF and cubic AC OPF model provides LMP calculation results very similar to each other while the calculation time of cubic AC OPF model is faster than that of the Full AC OPF. Other simplified OPF models, quadratic AC OPF, linear AC OPF and DC OPF offer erroneous results even though the calculation times are much faster than the Full AC OPF and the Cubic AC OPF. Given the condition that the OPF models sometimes fail to find the optimal solution due to the severe complexity of the Korean transmission power system, the Full AC OPF should be used as the primary OPF model while the Cubic AC OPF can be a promising backup OPF model for the LMP calculations and/or real-time operation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.1
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• pp.41-43
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• 2014

In this paper, we proposed a new protection scheme of the WDM mesh networks that can utilize the network resources efficiently while satisfying with the recovery time defined in the SLA (service level agreement). The protection scheme and the backup path are selected based on the comparison of the expected protection time with the SLA recovery time. The superior performance of the proposed protection scheme was demonstrated by comparing with ones of the existing protection schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.2
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• pp.371-388
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• 2014

Cognitive Radio (CR) has been recently proposed as a promising technology to remedy the problems of spectrum scarcity and spectrum underutilization by enabling unlicensed users to opportunistically utilize temporally unused licensed spectrums in a cautious manner. In Cognitive Radio Ad Hoc Networks (CRAHNs), data routing is one of the most challenging tasks since the channel availability and node mobility are unpredictable. Moreover, the network performance is severely degraded due to large numbers of path failures. In this paper, we propose the Fault-Tolerant Cognitive Ad-hoc Routing Protocol (FTCARP) to provide fast and efficient route recovery in presence of path failures during data delivery in CRAHNs. The protocol exploits the joint path and spectrum diversity to offer reliable communication and efficient spectrum usage over the networks. In the proposed protocol, a backup path is utilized in case a failure occurs over a primary transmission route. Different cause of a path failure will be handled by different route recovery mechanism. The protocol performance is compared with that of the Dual Diversity Cognitive Ad-hoc Routing Protocol (D2CARP). The simulation results obviously prove that FTCARP outperforms D2CARP in terms of throughput, packet loss, end-to-end delay and jitter in the high path-failure rate CRAHNs.

• ETRI Journal
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• v.29 no.3
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• pp.281-291
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• 2007

Wearable computers consisting of various small devices such as smart phones, digital cameras, MP3 players and specialized I/O devices in personal area networks will play an important role in future ubiquitous computing. In this environment, accessing user data is quite complex due to the dynamic and heterogeneous characteristics of the underlying networks. Moreover, since the amount of user data increases rapidly, automatic data backup management is also critical. To overcome these challenges, several studies have been conducted including our previously proposed file service system, PosCFS, which could be adapted to the requirements with a virtualization technique allowing per-user global namespace for managing and accessing data stored on physical storage spaces detected in PAN. In this paper, we present a smart file service framework, PosCFS+ which is an improved and extended version of our previous work. Performance improvement is made possible by redesigning the metadata management scheme based on database and keywords rather than ontology. In addition, the automatic data replication management is newly designed based on the OSD protocol.

• The Journal of Society for e-Business Studies
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• v.8 no.3
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• pp.165-176
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• 2003

Instead of existing cell phones, PDAs are observed as leading wireless Internet devices recently Numerous applications are developed by extended usage of PDAs and it should be installed appropriately according to devices. Furthermore, when battery is discharged, all data stored in RAM(Random Access Memory) becomes obsolete. So it should be recovered or reinstalled from flash memory, backup media or something. In this paper, we present an automatic application installation system(PAIS : PDA Automatic Installation System) to solve problems that users have to install applications by themselves whenever it is necessary. With this system, users feel comfortable by saving time and effort to install each applications and application development companies save cost needed to make materials illustrating installation process. Consequently PAIS may flourish wireless Internet business.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.110.1-110.1
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• 2016

국내외 최첨단 반도체 및 평판 디스플레이 공정에서 필요한 개별 건식 진공펌프들의 자기진단을 통한 예지보수의 실시간 구현 장치 개발과제의 2차년 전반기 수행된 연구결과의 일부를 본 논문에서 소개한다. 본 연구에서 최종 목표로 설정하고 있는 "smart" 진공펌프란 운전상태에 관련된 변수들의 측정치를 기반으로 한 자기진단 (self-diagnostics) 기능을 내장한 차세대 공정용 진공펌프를 의미한다. 1차년에 선정된 상태진단용 진공펌프의 상태변수(state variable)들의 효과적인 수집을 구현하기 위한 연구가 진행되었다. 기존의 반도체 공정용 진공펌프들에서 측정하고 있는 상태변수로는 온도, 유량, 배기관 압력, 모터 소비전류 등과 같은 정적인 변수들뿐 아니라, 회전기계류의 상태진단에 필수적인 진동신호를 추가한 상태 변수 수집 장치를 개발하였다. 본 연구팀은 진공펌프의 회전진동을 유발하는 대표적인 부품은 회전체, 베어링, 그리고 치차로 이들 3 종의 회전진동성분들을 효과적으로 측정할 수 있는 신호처리 기법을 개발하였다. 금번 연구에서 채택한 진동신호 처리기법은 초고속 FFT 변환 기반의 주파수 대역 별 진동 레벨 환산과 더불어 다단계로 구성된 디지털 필터 (multi-staged decimation filter) 기법을 개발 적용하였다. 이러한 신호처리 기법을 통하여 측정된 진동 신호로부터 회전체, 베어링, 그리고 치차의 회전 진동성분을 효과적으로 측정하는 방법을 금번 학술대회에서 소개한다. 그리고, 진공펌프 상태진단에 필요한 상태변수의 실시간 backup 방법, 그리고 공정관리 server와 통신기능, 그리고 펌프 현장 관리자용 PC와 통신 기법 등 상태변수 측정 모듈의 확장성에 대한 기술적 내용을 소개한다.