• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.10
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• pp.783-790
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• 2018

The frequency-hopping technique is one of the spread-spectrum techniques. Frequency hopping is a communication system in which the carrier frequency channel is hopped within the wideband. Therefore, a frequency-hopping system has such advantages as antijamming and low probability of intercept. This system is often used in military communications. Because frequency-hopping signal detection is difficult, it is an important research issue. A novel detection technique is proposed that can improve detection probability. When the received signal is transformed to a frequency domain sample by fast Fourier transform, spectral leakage lowers the detection probability. This problem can be solved by using the Hamming window, and the detection probability can be increased. However, in a frequency-hopping environment, the windowing technique lowers the detection probability. The proposed method solves this weakness. The simulation results show that the proposed detection technique improves the detection probability by as much as 13 %.

• Journal of the Korean Society of Industry Convergence
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• v.5 no.3
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• pp.233-238
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• 2002

본 논문에서는 유도가열조리기의 효과적인 설계를 위하여 입력주파수 변화에 따른 유도가열조리기의 자계와 열계 해석 방법을 제시하였다. 유도가열조리기의 내부자계는 3차원 축대칭 유한요소법을 사용하여 해석하였으며, 열원은 유도가열조리기의 내부에서 유도된 와전류에 의하여 발생되고, 열은 열원과 열방정식을 사용하여 계산되어진다. 또한, 유도가열조리기의 온도특성을 스테인레스와 알루미늄 각각에 대하여 주파수와 투자율에 따라 제시하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.113-116
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• 1993

본 논문에서는 변형된 wavelet 변환을 통해 추출한 특징벡터를 이용하여 한국어 숫자음을 대상으로 한 음성인식기를 구현하였다. wavelet 변환은 시간 및 주파수 영역에 대해 다중해상도(multiresolution)를 가지는 신호분석법이다. 본 연구에서는 계산량의 감소와 넓은 주파수 대역을 분석하기 위해, mother wavelet의 형태를 분석 주파수 대역에 따라 변화시키는 방법을 제안하였다. 기존의 wavelet 변환으로 실험한 결과 86.5%의 인식율을 얻었고, 변형된 wavelet 변환의 경우 96%의 인식율을 얻었으며 계산량이 감소하였다. 이와 함께 음성인식에서 널리 사용되는 특징 파라미터인 멜켑스트럼과 FFT 멜스케일 필터 대역(mel scale filter bank)과 비교 실험한 결과 인식율의 향상을 보였다. 이는 제안한 방법이 고주파 대역의 세밀한 시간 해상도와 저주파 대역의 세밀한 주파수 해상도를 지니는데 기인하는 것으로 판단된다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.898-906
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• 2002

In this paper, we investigated the improvement degree of transmission distance of the various initial frequency chirped optical pulse with 5 dBm initial power dependence on the various bit rate and fiber dispersion coefficient, when MSSI(Mid-Span Spectral Inversion) with the optimal pump power condition is adopted for the compensation method for optical pulse distortion. And we analyzed the influence of mutual relation of optical pulse frequency chirp and Kerr effect on the MSSI methods for the long-haul optical transmission through the computer simulation. We found that the compensation degree of distorted optical pulse varies as a consequence of the variation of combined phase modulation of self phase modulation(Kerr effect) and initial frequency chirp parameter dependence on the fiber dispersion coefficient. And we found that, if the transmission bit rate is increased k times, the dispersion coefficient value of dispersion shift fiber is decreased $2^k$ times so as to be almost the same performance of the transmission system with k times lower bit rate.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.9 no.2
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• pp.35-41
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• 1995

This paper proposes an adaptive methodology for setting of the underfrequency relays that is based on the initial rate of change of the frequency decline to protect for excess frequency decline of power system under large generator outage. The strategy of the load shedding is as follows : Let the load shedding of the first step occur when the frequency reaches 59.5 (Hz), and the load shedding power of this first and second step be one half of the total "Static Load Shed" value for any given disturbance size based on the initial rate of change of the frequency. As a results, it is verified that the use of the proposed method is more efficient than the conventional method in the characteristic of the frequency recovery. recovery.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.5
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• pp.900-905
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• 2008

I perform bit error rate(BER) analysis of orthogonal frequency division multiplexing(OFDM) systems impaired by both direct current(DC) offset and carrier frequency offset. By analyzing the BER performance for real OFDM systems employing 16-quadrature amplitude modulation(QAM) and pilot symbol estimation, the dependency of BER on the DC offset and carrier frequency offset is quantified and compared to ideal performance. Results show that the magnitude of frequency offset and DC offset are required to be less than 0.01 and 0.007, respectively.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2003.11a
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• pp.165-167
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• 2003

무전극 형광 램프에서 플라즈마 생성이 용이한 유도 결합형 플라즈마가 많이 사용되는데, 코일의 권선수나 주파수에 의해 전기적 특성의 변화가 크다. 따라서, 기존의 환형 무전극 형광 램프에 사용되는 ferrite core나 coil을 새롭게 적용하기 위하여 투자율이 2000인 Mn-Zn ferrite를 사용하여 주파수와 coil의 권선수를 변화시켜 전기적 특성을 측정하여 기존의 환형 무전극 형광램프와 비교·검토하였다.

• Journal of the Korea Safety Management & Science
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• v.12 no.3
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• pp.135-143
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• 2010

본 연구에서는 대기오염물질인 유해 황산화물 가스를 이산화티탄 촉매 반응기와 연면 방전 반응기를 조합한 반응기에서 플라즈마 방전반응에 의하여 주파수 변화, 체류시간, 전극의 굵기, 첨가 모의가스 등의 공정 변수를 변화 시켜 분해제거 실험을 하였다. 실험 결과 황산화물의 분해제거 실험에서 주파수 10kHz에서 소비전력 19W에서 분해제거율은 99%이었으며 이산화티탄 촉매반응기를 부착한 경우가 없는 경우보다 5%이상 증가효과가 이었다. 첨가가스로 메탄을 첨가한 경우 분해제거율이 증가하였고, 산소농도가 높아질수록 증가하였다 또한 이산화 탄소를 첨가한 경우 분해율은 감소하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1A
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• pp.1-11
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• 2009

In OFDMA or SC-FDMA systems one can generate time varying channels or frequency selective channels using multiple transmit antennas to achieve diversity without special space-time processing at the receivers. While low channel coding rate needs to be used for distributed-allocation SC-FDMA systems with a phase rolling technique to produce time fluctuation, relatively high channel coding rate can be used when cyclic delay diversity is used to increase frequency selectivity assuming quasi-static channel. On the other hand, for block-hopping SC-FDMA systems there is no significant difference between two diversity techniques in terms of optimal channel coding rates.

• Journal of the Korean Applied Science and Technology
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• v.35 no.3
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• pp.676-682
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• 2018

In order to study electrical properties of epoxy composites with various frequency. To measure of dielectric characteristics have been performed over a frequency range from 30[Hz] to 3[MHz] and a temperature range of $20[^{\circ}C]$, $100[^{\circ}C]$, $140[^{\circ}C]$. We observed values of dielectric constant and dissipation of the epoxy composites with various frequency. We were observed dielectric loss and dispersion in low frequency region. Also, we observed to decrease of the dielectric constant due to the effects of filler in high temperature region.