• ETRI Journal
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• v.37 no.3
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• pp.460-470
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• 2015

Orthogonal frequency-division multiplexing (OFDM) is one of the most widely used technologies in current wireless communication systems and standards. Cognitive radio (CR) provides a robust solution to the problem of spectrum congestion as it offers opportunistic usage of frequency bands that are not occupied by primary users. Due to the underlying sensing, spectrum shaping, scaling, and interoperable capabilities of OFDM, it has been adapted as a best transmission technology for CR wireless systems. However, the performance of an OFDM-based CR wireless system is affected by the existence of narrowband interference (NBI) from other users. Further, due to carrier frequency offset in NBI sources, NBI energy may spread over all subcarriers of an OFDM signal. In this paper, a fixed Amplify-and-Forward (AF) relay that operates at a frequency band that is different from that of direct mode is introduced to suppress the effect of NBI. Analytical expressions are derived for outage probability in direct, AF-relay, and incremental relaying modes. The outage performance of the proposed AF relay-based CR network is proven to be better than that of direct mode.

• Journal of the Korean Society of Safety
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• v.38 no.1
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• pp.18-24
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• 2023

Severe natural disasters and man-made attacks such as terrorism are causing unprecedented disruptions in power systems. Due to rapid climate change and the aging of energy infrastructure, both the frequency of failure and the level of damage are expected to increase. Resilience is a concept proposed to respond to extreme disaster events that have a low probability of occurrence but cause enormous damage and is defined as the ability of a system to recover to its original function after a disaster. Resilience is a comprehensive indicator that can include system performance before and after a disaster and focuses on preparing for all possible disaster scenarios and having quick and efficient recovery actions after an incident. Various studies have been conducted to evaluate resilience, but studies on economic damage considering the duration of a power outage are scarce. In this study, we propose an optimal algorithm that can identify failures after an extreme disaster and restore the load on the distribution system through emergency distributed power generation input and system reconfiguration. After that, the cost of power outage damage is analyzed by applying VoLL and CDF according to each restoration strategy.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.5
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• pp.67-72
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• 2014

In this paper, an energy harvesting scheme is applied in the cooperative communication. The proposed scheme uses an energy harvesting relay in which the relay harvests the energy from the source node and transfers to the power form in forwarding the received data to the destination node. The well-known maximal ratio combining (MRC) technique is applied to increase the diversity gain at the destination. Therefore, with applying the proposed energy harvesting scheme, the limited power at the relay is solved, and the operation efficiency of the network and the mobile devices is improved. Finally, performance of the proposed protocol is analyzed in terms of bit error rate, outage probability, power collection efficiency.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.3
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• pp.423-431
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• 2022

The UPS(Uninterruptible Power Supply) system operates in the battery charging mode when the grid is normal, and in the UPS mode, which is the battery discharge mode when a grid error occurs. Since the UPS must supply the same voltage as the grid to the load within 4 [ms] in case of a grid error, the switching time and power recovery time should be short when controlling the output voltage and current of the UPS, and the power failure detection time is also important. The power outage detection algorithm using DFT(Discrete Fourier Transform) proposed in this paper compares the grid voltage waveform with the voltage waveform including the 9th harmonic generated through DFT using Schmitt trigger to detect power outage faster than the existing power outage monitoring algorithm. There are advantages. Therefore, it is possible to supply instant and stable power when switching modes in the UPS system. The multi-power-applied UPS system proposed in this paper uses DFT, which is faster than the conventional blackout monitoring algorithm in detecting power failure, to provide stable power to the load in a shorter time than the existing power outage monitoring algorithm when a system error occurs. The detection method was applied. The changeover time of mode switching was set to less than 4 [ms], which is 1/4 of the system cycle, in accordance with KSC 4310 regulation, which was established by the Industrial Standards Council on the regulation of uninterruptible power supply. A 10 [kW] UPS system in which commercial voltage, vehicle generator, and auxiliary diesel generator can be connected to each of the proposed transfer devices was constructed and the feasibility was verified by conducting an experiment.

• Journal of information and communication convergence engineering
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• v.14 no.3
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• pp.171-176
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• 2016

In this study, we investigate the physical layer secrecy performance of RF energy harvesting (EH) networks over Rayleigh fading channels. The RF-EH system considered here consists of one power transfer station, one source, one destination, and multiple passive eavesdroppers. The source harvests energy from the power transfer station and transmits the information to the destination by using a time switching-based relaying protocol. The eavesdroppers try to extract the transmitted information without an active attack. By using the statistical characteristics of the signal-to-noise ratio (SNR), the exact closed-form expressions of the existence probability of the secrecy capacity and the secrecy outage probability are derived. Further, we analyze the secrecy performance of the system with respect to various system parameters, such as the location of the system elements and the number of eavesdroppers. Finally, the equivalent Monte Carlo simulation results are provided to confirm the correctness of our calculations.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.95-96
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• 2006

As the power industry moves towards open competition, there has been a call for methodology to evaluate distribution power system reliability by using customer interruption costs. Accordingly, it is increased for methodology to evaluate distribution power system reliability in power supply zones under competitive electricity market. This paper presents algorithm to evaluate system average interruption duration index. expected energy not supplied and system outage cost taking Into consideration failure rate of distribution facility and industrial customer interruption cost. Also, to apply this algorithm to evaluate system outage cost presented in this paper, distribution system of a dual supply system consisting of mostly high voltage customers in industrial complex in Korea is used as a sample case study. Finally, evaluation results of system interruption cost, system average interruption duration index and expected energy not supplied in sample industrial complex area are shown in detail.

• Proceedings of the KIPE Conference
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• 2004.07b
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• pp.570-574
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• 2004

This paper deals with a novel 3-phase power quality disturbance generator. The proposed generator can be applied to the performance that of custom power devices. Voltage sag, swell, outage unbalance and phase shift are provided by the generator. The control scheme for the disturbance generation is simple, and hardware setup is cost effective compared with conventional scheme. The operating principle of the generator is described and the usefulness verified through simulation with 10kVA power rating.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.1
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• pp.260-279
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• 2015

In this paper, we investigate physical layer security for multiple decode-and-forward (DF) relaying underlay cognitive radio networks (CRNs) with fixed transmit power at the secondary network against passive eavesdropping attacks. We propose a simple relay selection scheme to improve wireless transmission security based on the instantaneous channel information of all legitimate users and the statistical information about the eavesdropper channels. The closed-form expressions of the probability of non-zero secrecy capacity and the secrecy outage probability (SOP) are derived over independent and non-identically distributed Rayleigh fading environments. Furthermore, we conduct the asymptotic analysis to evaluate the secrecy diversity order performance and prove that full diversity is achieved by using the proposed relay selection. Finally, numerical results are presented to verify the theoretical analysis and depict that primary interference constrain has a significant impact on the secure performance and a proper transmit power for the second transmitters is preferred to be energy-efficient and improve the secure performance.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1998.05a
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• pp.211-219
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• 1998

전력의 공급지장비 추정은 이질적 경제권간에는 물론이고 동일 경제권 내에서도 추정치가 사례별로 다양한 분포를 갖고 있다. 따라서 일정 목적을 갖고 공급지장비를 추정할 때에는 유사한 목적, 시대 그리고 추정분야에 대한 기존의 사례를 조사하여 참조하여 비교할 필요가 있다. 이러한 점에서 본 연구는 전력의 공급지장비 주요 추정사례를 1948년 스웨덴의 경우 이후 최근에는 1997년 칠레와 이스라엘의 사례까지 조사하여, 이를 추정부문별로 재정리하였다.

• Journal of Radiation Protection and Research
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• v.34 no.4
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• pp.176-183
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• 2009

Maintenance on the water chamber of steam generator during outage in nuclear power plants (NPPs) has a likelihood of high radiation exposure to whole body of workers even short time period due to the high radiation exposure rates. In particular, it is expected that hands would receive the highest radiation exposure because of its contact with radiation materials. In this study, characteristic analysis of inhomogeneous radiation fields for contact operations was conducted using thermoluminescent dosimeter (TLD) readouts from the application tests of two-dosimeter algorithm to Korean NPPs in 2004. It is regarded that inhomogeneous radiation fields for contact operations in NPPs are dominated by high energy photons. In addition, field tests for workers who participated in maintenance on the steam generator during outage at Ulchin NPPs in 2009 and pressure tube replacement at Wolsong NPPs in 2009 were conducted to analyze radiation fields and to estimate the extremity dose. As a result, radiation fields were dominated by high energy photons.