• Journal of Communications and Networks
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• 제9권1호
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• pp.34-42
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• 2007

Orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (TDM), in this paper called OFDM/TDM, can overcome the high peak-to-average-power ratio (PAPR) problem of the conventional OFDM and improve the robustness against long time delays. In this paper, the bit error rate (BER) performance of OFDM/FDM in a frequency-selective Rayleigh fading. channel is evaluated by computer simulation. It is shown that the use of frequency-domain equalization based on minimum mean square error criterion (MMSE-FDE) can significantly improve the BER performance, compared to the conventional OFDM, by exploiting the channel frequency-selectivity while reducing the PAPR or improving the robustness against long time delays. It is also shown that the performance of OFDM/FDM designed to reduce the PAPR can bridge the conventional OFDM and single-carrier (SC) transmission by changing the design parameter.

• 전기학회논문지P
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• 제50권3호
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• pp.101-108
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• 2001

Frequency is an important operating parameter of a power system. Electric power systems sustain transient frequency swings whenever the balance between generation and load does not no longer hold. To cope with this constraints, it requires an accurate and high speedy frequency deviation estimation technique and suitable adjustment to obtain the Power system energy balance. This paper describes a digital signal processing technique for measuring the operating frequency of a power system. The fundamental frequency component of 3-phase signal is first extracted by using an algorithm based on FIR filter. The rate change of the phase angle is used for estimation. To confirm the validity of the proposed algorithm, the simulation studies carried out on a typical 154KV double T/L system by using EMTP software. Some test results are presented in the paper.

• 한국의상디자인학회지
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• 제22권3호
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• pp.49-61
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• 2020

This study analyzed the social media accounts and performed a Big Data analysis of Z-generation fashion using Textom Text Mining Techniques program and Ucinet Big Data analysis program. The research results are as follows: First, as a result of keyword analysis on 67.646 Z-generation fashion social media posts over the last 5 years, 220,211 keywords were extracted. Among them, 67 major keywords were selected based on the frequency of co-occurrence being greater than more than 250 times. As the top keywords appearing over 1000 times, were the most influential as the number of nodes connected to 'Z generation' (29595 times) are overwhelmingly, and was followed by 'millennials'(18536 times), 'fashion'(17836 times), and 'generation'(13055 times), 'brand'(8325 times) and 'trend'(7310 times) Second, as a result of the analysis of Network Degree Centrality between the key keywords for the Z-generation, the number of nodes connected to the "Z-generation" (29595 times) is overwhelmingly large. Next, many 'millennial'(18536 times), 'fashion'(17836 times), 'generation'(13055 times), 'brand'(8325 times), 'trend'(7310 times), etc. appear. These texts are considered to be important factors in exploring the reaction of social media to the Z-generation. Third, through the analysis of CONCOR, text with the structural equivalence between major keywords for Gen Z fashion was rearranged and clustered. In addition, four clusters were derived by grouping through network semantic network visualization. Group 1 is 54 texts, 'Diverse Characteristics of Z-Generation Fashion Consumers', Group 2 is 7 Texts, 'Z-Generation's teenagers Fashion Powers', Group 3 is 8 Texts, 'Z-Generation's Celebrity Fashions' Interest and Fashion', Group 4 named 'Gucci', the most popular luxury fashion of the Z-generation as one text.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.440_441
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• 2009

The standard for the frequency protection of distributed generation in Korea Electric Power Corporation (KEPCO)'s standard doesn't include the setting of frequency protection. Therefore, this paper analyzes the correlation between the frequency protection requirements and the stability of grid-connected PV system for the adjustable operating setting of frequency protection. The distribution system interconnected with 3 MW PV system is modeled by Matlab/Simulink. The various value of frequency is simulated. For studied cases, the stability of PV system is analyzed. It is concluded that the operating setting of frequency protection can be determined by the stability of PV system.

• 한국통신학회논문지
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• 제33권10A호
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• pp.964-971
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• 2008

본 논문에서는 채널이 시간 및 주파수에서 비선택적일 때를 가정하여 복수의 송신 안테나를 사용하는 SC-FDE(Single Carrier with Frequency Domain Equalization) 시스템에서 순환지연 다이버시티 기술과 위상 회전 기술의 성능을 비교한다. OFDM(Orthogonal Frequency Division Multiplexing) 시스템에서는 위상 회전을 이용하여 시간축에서 변화하는 채널을 만드는 것과 순환지연 다이버시티를 사용하여 주파수 선택적 채널을 만드는 것은 유사한 성능을 보인다. 그러나 SC-FDE 시스템에서는 시간축에서 변화하는 채널을 만드는 것이 주파수축에서 변화하는 채널을 만드는 것보다 더 우수한 성능을 보일 수 있다.

• Journal of information and communication convergence engineering
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• 제21권1호
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• pp.1-8
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• 2023

This paper presents a design method for a wideband bandpass filter (BPF) which compensates for frequency dependency based on the image admittance and image phase. In the proposed method, new compensation methods for the admittance and phase are integrated with the conventional method. The proposed method improves the frequency shift and reduces the unwanted bandwidth when designing more than 20% of the Fractional Bandwidth (FBW), whereas the conventional method exhibits frequency degradation at only 10% FBW. The proposed design theory was verified by applying it to both lumped elements and distributed lines through circuit simulation and measurements without an optimization process. The measurement results demonstrate improvements in the frequency shift and target bandwidth. In the future, an accurate design method based on frequency dependence can be implemented for the next-generation broadband communication system applications.

• 한국정보전자통신기술학회논문지
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• 제10권1호
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• pp.85-94
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• 2017

본 논문에서는 동물소리 인식시스템을 위하여 최대 빈도모델 탐색 알고리즘을 고안하고 이를 이용한 소리모델을 생성하는 방법을 제안하였다. 소리모델 생성 방법은 동물종의 소리 데이터로부터 학습과정, 비터비 탐색과정 및 최대 빈도모델 탐색과정을 반복하면서 HMM(Hidden Makcov Model)모델의 구조(상태의 수와 GMM의 수)를 탐색하여 최적의 인식률을 갖는 모델집합이 생성하는 방법이다. 최대 빈도모델 탐색 알고리즘은 입력 소리 데이터를 비터비(Viterbi) 알고리즘으로 탐색하여 모델리스트를 생성하고 이 리스트 중에서 최대 빈도수의 모델을 탐색하여 최종 인식결과로 결정하는 방법이다. 알고리즘에서 소리특징으로 MFCC(Mel Frequency Cepstral Coefficient), 모델형식으로 HMM을 이용하고 C# 프로그래밍언어로 구현 하였다. 알고리즘의 성능을 평가하기 위하여 27종의 동물소리를 선정하고 실험을 하였으며 27개의 HMM 모델집합이 97.29 퍼센트의 인식률로 생성됨을 확인하였다.

• 디지털융복합연구
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• 제9권4호
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• pp.169-179
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• 2011

본 연구의 목적은 인구통계학적 특성에 따른 디지털컨버전스 수준을 분석하며, 디지털기기와 디지털서비스의 사용빈도에 다른 컨버전스 수준을 분석하고자 한다. 연구방법으로는 FGI, 전문가 자문그룹과 인터뷰와 설문분석을 수행하였다. 연구결과, 30대, 대학원이상의 고등교육을 받은 사람들이 디지털컨버전스 기기와 서비스에 적극적으로 참여하였으며, 소비자들이 사용하는 컨버전스 기기중 컨버전스 수준이 높은 기기는 스마트폰, 타블렛 PC, 넷북의 순서로 높이 나타났으며, 컨버전스 서비스에서는 SNS, 트위터, UCC, 포탈 메시지, 앱스토아, e-Book 웹하드의 순서로 나타났다. 컨버전스 세대들은 스마트폰을 활용한 앱스토아, 무선 게임을 즐기며, 페이스북/싸이월드, 트위터, 포탈과 인터넷 커뮤니티 서비스에 많이 참여하고 있는 것으로 나타났다.

• 조명전기설비학회논문지
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• 제15권6호
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• pp.103-110
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• 2001

최근 오존은 그 효용성을 인정받아 다양한 분야에서 사용되고 있으며, 그 수요 또한 계속 증가하는 추세이다. 이에 다양한 종류의 오존발생기가 연구되어지고 있다. 이러한 오존발생기는 모두 고농도와 고수율을 얻는데 그 연구목표가 있다고 할 수 있으며, 그중 하나가 동축원통형 오존발생기이다. 본 논문에서는 고주파 전원을 사용하는 새로운 형태의 원통형 오존발생기를 제안하였으며, 오존발생기의 전극 간극의 변화에 따른 방전특성과 오존생성특성을 연구하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.867-872
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• 2002

A high intensity acoustic test facility is constructed at Korea Aerospace Research Institute (KARI) by 2003. The reverberant chamber of the facility has a volume of 1,228 cubic meters and shall provide an acoustic environment of 152 dB over the frequency range of 25 Hz to 10,000 Hz. The facility consists of a large scaled reverberant chamber, acoustic power generation systems, gases nitrogen supply systems, and acoustic control systems. This paper describes how the basic parameters of a chamber and power generation systems are controlled to meet the requirement of the test. The volume of a reverberant chamber is controlled by the size of test objects and the reverberant characteristics of a chamber. The capacity of acoustic power generation systems is determined by the energy absorption of a chamber and the efficiency of acoustic modulators. Simple math is employed to calculate the required power of acoustic modulators. Moreover, the paper explains how the distribution of sound pressure level at low frequency is checked by analytical and numerical methods.