• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.1
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• pp.179-187
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• 2014

The underlay protocol is a cognitive radio method in which secondary or cognitive users use the same frequency without affecting the quality of service (QoS) for the primary users. In addition, because of the broadcast characteristics of the wireless environment, some nodes, which are called eavesdropper nodes, want to illegally receive information that is intended for other communication links. Hence, Physical Layer Security is applied considering the achievable secrecy rate (ASR) to prevent this from happening. In this paper, a performance analysis of the amplify-and-forward scheme under an interference constraint and Physical Layer Security is investigated in the cooperative communication mode. In this model, the relays use an amplify-and- forward method to help transmit signals from a source to a destination. The best relay is chosen using an opportunistic relay selection method, which is based on the end-to-end ASR. The system performance is evaluated in terms of the outage probability of the ASR. The lower and upper bounds of this probability, based on the global statistical channel state information (CSI), are derived in closed form. Our simulation results show that the system performance improves when the distances from the relays to the eavesdropper are larger than the distances from the relays to the destination, and the cognitive network is far enough from the primary user.

• Journal of Korean Society for Quality Management
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• v.23 no.4
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• pp.128-147
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• 1995

An accelerated life testing(ALT) for aluminum electrolytic capacitors is conducted and analyzed. A testing equipment, which consists of part fixtures, relay board, controller, video bridge and microcomputer, is made for the ALT. Load factors are temperature with four levels and voltage with three levels. Base on 'optimized 4:2:1 plan', 2,000 electrolytic capacitors are allocated at 12 experimental conditions(; 4 levels of temperature ${\times}3$ levels of voltage), and the ALT is conducted. From the experimental results, an acceleration model is derived and acceleration factors are estimated. A discussion on the experimental results is included.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.8
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• pp.1460-1466
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• 2011

This paper proposes the algorithm for discriminating faults from the variation due to the operation of non-linear components to prevent the mal-operation of protection relay in the distribution system. An IEEE 13 node test feeder is modeled to analyze the characteristics of the fault and each variation using EMTP-RV. Simulations with various operating conditions of transformers, non-linear loads, and unbalanced loads are performed using the test feeder model. Based on simulation results, the wavelet transform is adopted to analyze the current waveforms from the faults and variations to find out the differences between them and the algorithm for discriminating faults from the variation is proposed. The proposed algorithm is verified by using the current waveforms simulated in the KEPCO's distiribution system and IEEE 13 node test feeder.

• IE interfaces
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• v.24 no.4
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• pp.304-313
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• 2011

An Unmanned Aerial Vehicle(UAV) is a powered pilotless aircraft, which is controlled remotely or autonomously. UAVs are currently employed in many military missions(surveillance, reconnaissance, communication relay, targeting, strike etc.) and a number of civilian applications(communication service, broadcast service, traffic control support, monitoring, measurement etc.). For accomplishing the UAV's missions, guarantee of survivability should be preceded. The main objective of this study is the path planning to maximize survivability for UAV based on 3-dimensional environment. A mathematical programming model is suggested by using MRPP(Most Reliable Path Problem) and solved by transforming MRPP into SPP(Shortest Path Problem). This study also suggests a $A^*PS$ algorithm based on 3-dimensional environment to UAV's path planning. According to comparison result of the suggested algorithm and SPP algorithms (Dijkstra, $A^*$ algorithm), the suggested algorithm gives better solution than SPP algorithms.

• Journal of Korea Multimedia Society
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• v.14 no.12
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• pp.1559-1571
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• 2011

In wireless ad hoc networks, nodes communicate with each other using multihop routed transmission in which hop-by-hop cooperative diversity can be effectively employed. This paper proposes (i) two cooperation models for per-link cooperation (PLC) and per-node cooperation (PNC) for exploiting cooperative diversity in wireless ad hoc networks and (ii) a cooperative routing algorithm for the above models in which best relays are selected for cooperative transmission. First, two cooperation models for PLC and PNC are introduced and represented as an edge-weighted graph with effective link quality. Then, the proposed models are transformed into a simplified graph and a cooperative routing algorithm with O(n2) time is developed, where n is the number of nodes in the network. The effectiveness of the algorithm is confirmed for the two cooperation models using simulation.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.315-316
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• 2006

As IEC 61850 based substation automation technology is emerging globally, there are many efforts to implement and apply this IEC 61850 standard to substation automation area. IEC 61850 based substation supports ethernet network, standard data model and SCL(substation Configuration Language), etc. These features can provide enough environment to make applied technology which can substitute the legacy relay trip logic configuration method(PLC or Local area reconstruction) to XML based configuration method. This paper suggests new IED trip logic configuration method. The XML based trip logic configuration method can be established using SCL technology And IED trip logic reconfiguration from remote center can be possible under ethernet based technology

• Proceedings of the Korea Information Processing Society Conference
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• 2003.05b
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• pp.1321-1324
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• 2003

본 논문에서는 P2P를 사용한 방송모델을 소개한다. P2P 기술을 이용한 릴레이식 방송모델 시스템을 실질적으로 설계, 구현한다. 현재의 네트워크 인프라를 통해 서버-클라이언트 방송모델의 한계를 극복할 수 있는 방송모델의 구현을 목적으로 한다. 본 논문의 P2P를 이용한 릴레이식 방송 기술을 이용하여 실질적으로 인터넷 방송에 사용 할 수 있게 최적화된 시스템을 도출하고 그것을 통해 품질 높은 방송 시스템을 설계, 구현하였다. 기존의 서버-클라이언트 방송 모델에서의 여러 문제점 특히 다수의 사용자가 접속 시 접속 거부 또는 저 품질의 방송을 내보내는 현상을 P2P 기술을 통해 작업을 분담함으로써 접속자 수와 관계없이 방송 품질을 유지하고 인터넷 방송에서 품질에 대한 신뢰성을 유지 할 수 있는 시스템을 구축한다.

• Proceedings of the Korea Society for Simulation Conference
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• 2001.10a
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• pp.110-115
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• 2001

Today, effective utilization of sophisticated networks greatly influences the activities of a business, making performance evaluations of computer network systems a necessity, We have developed a special computer network simulator capable of automatically generating a model based on data accumulated by a network analyzer to guide the user in selecting ideal parameters. The simulator was developed to provide user-friendly analysis for engineers involved in the actual network design. This paper gives an overview of the simulator and describes an example application of evaluating a network design that anticipates the future increase in traffic for a company introducing voice over frame relay (VoFR) into a wide area network (WAW).

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1008-1011
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• 1996

Most control systems of power plants are using classical PID controllers for their process control. In order to get the desired control performances, the correct tuning of PID controllers is very important. Sometimes, it is necessary to retune PID controllers after the change of system operating condition and system design change, etc. Commercial auto-tuning controllers such as relay feedback controller can be used for this purpose. However, using these controllers to the safety-critical systems of nuclear power plants may be cause of unsafe operation, because they are using test signals for tuning. A new system identification auto-tuning method without using test signal has been developed in this paper. This method uses process input/output signals for system identification of unknown control process. From the model information of control process which was obtained from system identification approach, the optimal PID parameters can be calculated. The method can be used in the safety-critical systems because it is not using test signals during system modeling process.

• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1373-1375
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• 1999

High impedance fault (HIF) is defined as fault the general overcurrent relay can not detect or interrupt. Especially when HIF occur in residential areas, energized high voltage conductor results in fire hazard, equiment damage or personal threat. This paper proposes the model of HIF in transmission line using the ZnO arrester and resistance to be implemented within EMTP. Wavelet transform is efficient and useful for the detection of HIF in power system, because it uses variable windows according to frequency. HIF detection method using wavelet transform can distinguish HIF from similar phenomena like arcfurance load, capacitor bank switching and line switching.