• Journal of Communications and Networks
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• v.7 no.3
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• pp.385-393
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• 2005

In this paper, we propose a simple algorithm to adaptively adjust the value of dupthresh, the duplicate acknowledgement threshold that triggers the transmission control protocol (TCP) fast retransmission algorithm, to improve the TCP performance in a network environment with persistent packet reordering. Our algorithm uses an exponentially weighted moving average (EWMA) and the mean deviation of the lengths of the reordering events reported by a TCP receiver with the duplicate selective acknowledgement (DSACK) extension to estimate the value of dupthresh. We also apply an adaptive upper bound on dupthresh to avoid the retransmission timeout events. In addition, our algorithm includes a mechanism to exponentially reduce dupthresh when the retransmission timer expires. With these mechanisms, our algorithm is capable of converging to and staying at a near-optimal interval of dupthresh. The simulation results show that our algorithm improves the protocol performance significantly with minimal overheads, achieving a greater throughput and fewer false fast retransmissions.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.166-168
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• 2002

This paper presents a new numerical algorithm suitable for defining recloser reclaims time and blocking automatic reclosing during permanent faults on overhead lines. It is based on terminal voltage input data processing. The decision if it is safe or not to reclose is determined from the voltage signal of faulted and tripped line phase using Total Harmonic Distortion factor calculated by Discrete Fourier Transform. The algorithm was successfully tested using signals recorded on the real power system. The tests demonstrate the ability of presented algorithm to determine the secondary arc extinction time and to block unsuccessful automatic reclosing of HV lines with permanent fault.

• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1082-1084
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• 1999

A fault detection of power system must be fast and correctly over input signal without relation to any disturbance. But, it is difficult to detect fault state for digital relay comparison of fault perfectly. In this Paper, we measure each Phase current and infer type of fault using ANFIS(Adaptive Neuro-Fuzzy Inference System).

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2017.11a
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• pp.41-43
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• 2017

본 논문에서는 IoS (Internet of Signage) 환경에서 실감형 데이터 전송을 위한 상황 인지 기반 적응형 전송기법을 적용하고 이를 분석한다. 사이니지 네트워크 환경에서는 임의적인 다중 경로 페이딩, 간섭 등과 같은 왜곡 요소가 존재할 수 있기 때문에 이를 대처하기 위해 무선 송신기에서는 채널 환경에 대한 인지 이후, 그에 따른 MCS (Modulation and Coding Scheme)를 선정 및 안테나 기법을 선정한다. MCS 및 안테나 기법 선정을 위해 무선 송신기에서는 사전에 알고 있는 통계적인 SNR (Signal-to-Noise Ratio) 값을 통해 문턱값을 계산하고, 수신 사이니지로부터 얻은 CSI (Channel State Information)와의 크기 비교를 한다. 시뮬레이션 결과에서는 상황 인지를 기반으로 매 순간 최적의 전송률을 달성할 수 있음을 볼 수 있다.

• Journal of Sensor Science and Technology
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• v.20 no.3
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• pp.162-167
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• 2011

In this paper, we propose a vision system using a field programmable gate array(FPGA) and a smart vision chip. The output of the vision chip is varied by illumination conditions. This chip is suitable as a surveillance system in a dynamic environment. However, because the output swing of a smart vision chip is too small to definitely confirm the warning signal with the FPGA, a modification was needed for a reliable signal. The proposed system is based on a transmission control protocol/internet protocol(TCP/IP) that enables monitoring from a remote place. The warning signal indicates that some objects are too near.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.208-211
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• 2008

Band-limited filtering will be applied to remove interference resulted from two neighbored channels in the transmission of KOMPSAT-5 X-Band image data. In that case, receiver in ground station should prepare righteous matched filter to avoid huge BER degradation depending on the matched filter of COTS receiver. As an effort to simulate the bandlimited filtering, test filter was designed and manufactured on the basis of main specification for output filter of KOMPSAT-5 satellite. Consequently, 1.8dB of BER degradation was measured at the output of test band-pass filter, but the degradation was downsized up to 0.4dB thanks to the adaptive matched filter of COTS receiver.

• Proceedings of the IEEK Conference
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• 2003.07e
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• pp.2064-2067
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• 2003

본 논문에서는 비트율 제어 (rate-control)와 혼잡 제어(congestion-control) 사이의 관계를 고려하여 비디오데이터의 전송량 변화에 따른 화질 증감의 관계를 조사하고, 전송 대역폭의 변화에 대한 화질 열화를 최소화하기 위한 비디오 데이터 전송량의 변화 조건을 제안하고자 한다. 비디오 데이터를 전송하는 경우에 혼잡 제어는 현 채널 상에서 가용 전송 대역폭(Available Transmission Bandwidth)을 예측하고, 비트율 제어는 예측한 전송 대역폭을 비디오 부호화기의 전송 비트율에 적응시킨다. AIMD 기반의 혼잡 제어 기법은 비디오 데이터의 목표 비트율 (target bit rate)을 변화시키게 되고 이러한 결과는 비디오 화질의 잦은 변동으로 인해 나쁜 영향을 준다. 이러한 문제를 해결하기 위해 QP, SNR, 비트량 사이의 관계를 이용한 적응적인 메커니즘을 제안하고자 한다

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.259-260
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• 2008

전력계통에서 발생하는 고장의 70-95%는 1선지락 고장이고, 1선지락 고장의 70-90%는 아크고장이다. 아크고장이 발생하였을 경우, 아크고장과 같은 일시고장을 제거하고 투입하는 방법으로 자동재폐로가 사용되며 적절한 자동재폐로는 계통의 신뢰도 향상과 안정도 유지의 역할을 수행한다. 또한 송전용량 증대 및 무효전력 제어를 위한 FACTS(Flexible AC Transmission System, 유연송전시스템)기기의 사용이 증가함에 따라 FACTS가 적용된 계통에서 자동재폐로 영향을 분석해야 할 필요가 있다. 따라서 본 논문에서는 다양한 계통 상황을 보기 위해 기존의 멀티에이전트 기반의 자동재폐로가 적용된 계통에 FACTS을 적용하여 자동재폐로시의 영향을 분석하였다. EMTP와 JADE(Java Agent DEvelopment framework)를 이용하여 자동재폐로 계통 및 멀티에이전트 시스템을 모의하였으며, SVC(Static VAR Compensator)에 의한 영향을 분석하였다.

• Journal of Electrical Engineering and Technology
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• v.8 no.3
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• pp.649-657
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• 2013

DTN flooding based routing protocol replicate the message copy to increase the delivery like hood that overloads the network resources. The probabilistic routing protocols reduce replication cost by forwarding the message to a node that holds high predictability value to meet its destination. However, the network traffic converges to high probable nodes and produce congestion that triggers the drop of previously stored messages. In this paper, we have proposed a routing protocol called as Connection frequency Buffer Aware Routing Protocol (CFBARP) that uses an adaptive method to maintain the information about the available buffer space at the receiver before message transmission. Furthermore, a frequency based method has been employed to determine the connection recurrence among nodes. The proposed strategy has performed well in terms of reducing message drop, message relay while increases the delivery probability.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.8 no.4
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• pp.201-206
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• 2009

The third generation mobile communications system requiring the reliable multimedia data transmission has provided with the reliable voice, data and video services over the variable propagation environment. However the broadband wireless multiple access technologies cause Inter Symbol Interference (ISI) or Multiple Access Interference (MAI) to degrade the performance of W-CDMA (Code Division Multiple Access) system. Constant Modulus Algorithm (CMA) which is frequently used as the adaptive blind equalizers to remove the interfering signal has ill-convergence phenomenon without proper initialization. In this paper, new blind equalization method based on conventional CMA is proposed to improve the channel efficiency, and through computer simulation this is tested over the time varying fading environment of mobile communication system. Consequently, new blind equalization method into concatenated Kalman filter with CMA is verified better than conventional CMA through adopting minimum mean square errors and eye-pattern obtained from algorithm are compared.