• Proceedings of the Korea Information Processing Society Conference
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• 2013.11a
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• pp.804-807
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• 2013

최근 클라우드 컴퓨팅에 대한 관심이 고조됨에 따라, 이를 활용한 데이터베이스 아웃소싱(Outsourcing)에 대한 연구가 활발히 진행되고 있다. 그러나 아웃소싱 된 데이터베이스는 사용자 개인 정보, 증권, 또는 의료 정보 등 민감한 정보를 포함하기 때문에 서비스 제공자로부터 수행한 질의 결과 데이터가 데이터 소유자로부터 생성된 데이터이며, 정확한 질의 결과를 포함하는지 확인하기 위한 질의 결과 무결성 검증 기법의 필요성이 대두되었다. 기존 질의 결과 무결성 검증 기법은 질의 결과에 포함되는 무결성 검증 데이터의 크기가 증가하여 검증 데이터 전송 오버헤드 증가 및 데이터 노출 위험 증가 문제를 지닌다. 따라서, 본 논문에서는 데이터 보호를 지원하는 암호화 데이터 기반 질의 결과 무결성 검증 기법을 제안한다. 제안하는 질의 결과 무결성 검증 기법은 암호화된 데이터 그룹을 주기 함수를 이용하여 재분할하고, 최종 데이터 그룹 id를 힐버트 커브를 통해 변환한다. 따라서, 검증 데이터 오버헤드를 감소시켜 효율적인 질의 처리를 지원하며, 그룹 id 변경을 통해 검증 데이터 유출 위험을 방지한다. 성능평가를 통해, 제안하는 기법이 기존 기법에 비해 질의 처리 시간 측면에서 평균 2배, 검증 데이터 오버헤드 측면에서 최대 20배의 성능을 개선함을 보인다.

• Korean Journal of Optics and Photonics
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• v.27 no.2
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• pp.61-66
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• 2016

We used transmission deflectometry to measure the three-dimensional shapes of optical components, and we used the Hilbert transform to retrieve the phases from measured deformed fringe images. Deflectometry is useful for measuring large-scale samples, and specular samples. We have retrieved the phases from deformed fringe images and Hilbert-transformed images, and have used the least-squares method to find the height information. We have verified that phase retrieval using Hilbert transform is useful by computer simulation and experiment.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.2
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• pp.92-98
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• 2015

Recently, buildings tend to be large size, complex shape and functional. As the size of buildings is becoming massive, the need for structural health monitoring (SHM) technique is increasing. Various SHM techniques have been studied for buildings which have different dynamic characteristics and influenced by various external loads. "Abnormal behavior point" is a moment when the structure starts vibrating abnormally and this can be detected by comparing between before and after abnormal behavior point. In other words, anomalous behavior is a sign of damage on structures and estimating the abnormal behavior point can be directly related to the safety of structure. Abnormal behavior causes damage on structures and this leads to enormous economic damage as well as damage for humans. This study proposes an estimating technique to find abnormal behavior point using Hilber-Huang Transform which is a time-frequency signal analysis technique and the proposed algorithm has been examined through laboratory tests with a bridge model using a shaking table.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.431-434
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• 2003

As a wavelet transform which is presented as a new technique of signal processing field has time and frequency localization capabilities, it's possible for multiresolution analysis as well as easy to analyze various signal. So it is being applied in many fields recently. And when two wavelet base were designed to form Hilbert transform pair, wavelet pair show superior performance than the existing DWT(discrete wavelet transform) in data detection of pulse type. Therefore in this paper, we detected position of impulse noise by using two dyadic wavelet base which is designed by truncated coefficient vector.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2560-2567
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• 2000

When spatially dense velocity distribution is measured by a scanning laser Doppler vibrometer, the Fourier transform method provides the real and imaginary parts of the mode shapes in the form of a polynomial. However the Fourier transform method is often impractical because the independent decomposition property of cosine and sine components into real and imaginary parts, respectively, does not hold due to the leakage problem which commonly occurs in the Fourier transform of harmonic signals. To deal with this problem, a Hilbert transform method is newly proposed in this article. The proposed method is free from the leakage problem and relatively robust to the scanning error. A simulation example is provided to verify the effectiveness of this method.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.392-397
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• 2001

This paper concerns on modal analysis of mechanical structures by using a continuous scanning laser Doppler vibrometer. In modal analysis the Hilbert transform based approach is superior to the Fourier transform based approach because of its fine accuracy and its flexible experimental settings. In this paper the Hilbert transform based approach is extended to measure area mode shape data of a structure by simply modifying the scanning pattern ranging the entire surface of the structure. The effectiveness of this proposed method is illustrated along with results of numerical simulation for a rectangular plate.

• The Journal of the Acoustical Society of Korea
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• v.26 no.6
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• pp.276-285
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• 2007

In this paper it was discussed and compared measured loudspeaker impedance curve with ones reconstructed by TS parameters estimated using four kinds of parameter estimation methods developed in frequency domain. Frequency dependent parameters were introduced and derived using least square error minimization technique. For known dynamic mass TS parameter estimation methods were reviewed and also proved non-uniqueness of these parameters by simulation method. Minimum phase transformation was adopted to derive phase information from magnitude of loudspeaker electrical impedance curve measured by one channel analyzer.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.12
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• pp.277-284
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• 2013

The analysis of phase synchronization characteristics from EEG signals is important for the understanding of information processing functionality in the brain network. In this paper, wavelet transformation(WT), Hilbert tansformation (HT), complex demodulation (CD) methods having time localization characteristics were applied to real evoked potential data and noise added simulation data with center frequencies corresponding to EEG bands for the estimation performance analysis of phase offset, phase changing point, and interband crosstalk. The WT is the best both in ${\delta}$, ${\theta}$, and ${\alpha}$ band signal decomposition, and in analyzing phase synchronization performance. The CD can be efficiently used in changing point detection under tolerant noise condition because of its abrupt performance degradation over noise endurance level. From experimental observations, the WT is the most suitable in phase synchronization application of EEG signal, and the CD can be affordable in restricted application such as changing point detection for higher bands than ${\delta}$. Particularly, WT and CD can be used to detect the changing instant of brain function by indirectly estimating the phase changing point.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.10
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• pp.1845-1851
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• 2007

Background noise and room reverberation are two causes of degradation in speech in listening situations. Many algorithms developed to enhance reverberant speech. In this paper we propose a dereverberation method for enhancement of speech using modified the linear prediction(LP) residual in reverberant room condition. The proposed dereberberation method based on the fact that the signification excitation of the vocal tract system takes place at the instant of glottal closure in voiced speech. Our method used delay information form each sensor, and we need reverberant signals from 3 sensors. We obtain a new LP residual signal using modified IP residual combination which derived form weighting of the LP residual and the Hilbert transform of LP residual. The nature of the coherently added Hilbert envelop has several large amplitude spikes because of the effects of noise and reverberation. This residual of the clean speech is used to excite the time-varying all-pole filter to obtain the enhanced speech. We achieved simulation of proposed algorithm for performance analysis in reverberation environment. The proposed algorithm improves substantially the quality of reverberant speech.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.187-188
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• 2015

본 논문은 시간영역에서 대칭좌표법을 사용한 전력품질 이벤트 검출에 관한 연구이다. sag, swell. interruption, harmonic, flicker, transients, notches, spike 등과 같은 전력품질 이벤트들이 이 방법으로 쉽게 검출된다. 본 방법은 웨이블릿, s-변환, 힐버트 변환 등의 방법이 가지고 있는 계산 부담이 없기 때문에 온라인 응용프로그램에 쉽게 사용될 수 있다. 단상 전력품질 이벤트 신호는 시간 영역에서 대칭요소를 계산하기 위하여 120도, 240도 위상차를 가지고 생성되는 다른 두 신호와 함께 이동되어 간다. 전력품질 이벤트 신호의 시작점(triggering point)은 역상분으로부터 쉽게 검출될 수 있고 이벤트는 정상분과 역상분의 합을 사용한 파형의 특징 분석으로 쉽게 분류될 수 있다. 시뮬레이션된 결과는 전력품질 이벤트의 검출과 분류를 위한 본 방법의 효과를 보여주기 위하여 다수의 전력품질 이벤트를 보여주고 있고 전력계통망 지락사고 시뮬레이션을 수행하여 유용성을 확인하였다.