• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.1274-1279
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• 2004

This paper proposes technique to detect ground fault in railway high voltage distribution lines. Overcurrent relay technique is widely used for detecting one line ground fault that occurs most frequently in railway high voltage distribution lines. However, ground fault in distribution line is usually high impedance fault with arc. Because the fault current magnitude measured in substation is very small, the conventional overcurrent relay can't detect the high impedance ground fault. Therefore this paper proposes the advanced technique using wavelet transform. It extracts D1 component from fault signals and detects fault comparing magnitude of D1 component in each phase. To evaluate this proposed technique, we model distribution system using PSCAD/EMTDC and extract various fault data. In conclusion this technique can detect ground fault including high impedance fault regardless of fault distance, fault impedance etc.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.698-701
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• 2005

This paper examines that is extracted certain information in forest areas within high resolution imagery based on wavelet transformation. First of all, study areas are selected one more species distributed spots refer to forest type map. Next, study area is cut 256 x 256 pixels size because of image processing problem in large volume data. Prior to wavelet transformation, five texture parameters (contrast, dissimilarity, entropy, homogeneity, Angular Second Moment (ASM≫ calculated by using Gray Level Co-occurrence Matrix (GLCM). Five texture images are set that shifting window size is 3x3, distance .is 1 pixel, and angle is 45 degrees used. Wavelet function is selected Daubechies 4 wavelet basis functions. Result is summarized 3 points; First, Wavelet transformation images derived from contrast, dissimilarity (texture parameters) have on effect on edge elements detection and will have probability used forest road detection. Second, Wavelet fusion images derived from texture parameters and original image can apply to forest area classification because of clustering in Homogeneous forest type structure. Third, for grading evaluation in forest fire damaged area, if data fusion of established classification method, GLCM texture extraction concept and wavelet transformation technique effectively applied forest areas (also other areas), will obtain high accuracy result.

• 대한전기학회논문지:전력기술부문A
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• 제49권9호
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• pp.425-432
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• 2000

Wavelet transform is a new method fro electric power quality analysis. Several types of mother wavelets are compared using voltage sag data. Investigations on the use of some mother wavelets, namely Daubechies, Symlets, Coiflets, Biorthogonal, are carried out. On the basis of extensive investigations, optimal mother wavelets for the detection of voltage sag are chosen. The recommended mother wavelet is 'Daubechies 4(db4)' wavelet. 'db4', the most commonly applied mother wavelet in the power quality analysis, can be used most properly in disturbance phenomena which occurs rapidly for a short time. This paper presents a discrete wavelet transform approach for determining the beginning time and end time of voltage sags. The technique is based on utilising the maximum value of d1(at scale 1) coefficients in multiresolution analysis(MRA) based on the discrete wavelet transform. The procedure is fully described, and the results are compared with other methods for determining voltage sag duration, such as the RMS voltage and STFT(Short-Time Fourier Transform) methods. As a result, the voltage sag detection using wavelet transform appears to be a reliable method for detecting and measuring voltage sags in power quality disturbance analysis.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.267-272
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• 1998

A new signal processing technique, the directional harmonic wavelet map(dHWM), is presented to characterize the instantaneous planar motion of a measurement point in a structure from its transient complex-valued vibration signal. It is proven that the auto-dHWM essentially tracks the shape and directivity of the instantaneous planar motion, whereas the phase of the cross-dHWM indicates its inclination angle. Finally, the technique is successfully applied to an automobile engine for characterization of its transient motion during crank-on/idline/engine-off.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권2호
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• pp.883-900
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• 2017

In this paper block based blind secure gray image watermarking scheme based on discrete wavelet transform and singular value decomposition is proposed. In devising the proposed scheme, security is given high importance along with other two requirements: robustness and imperceptibility. The use of discrete wavelet transform not only improves robustness but the selection of bands with high tolerance towards noise caused an improvement in terms of imperceptibility. The robustness further improved due to the involvement of singular vectors along with singular values in watermark embedding and extraction process. Finally, to achieve security, the selected DWT band is decomposed into smaller blocks and random blocks are chosen for modification. Furthermore, the elements of left and right singular vectors of selected blocks are chosen based on their dependence upon each other for watermark embedding. Various experiments using different images as host and watermark were conducted to examine and validate the proposed technique. Additionally, the proposed technique is tested against various attacks like compression, affine transformation, cropping, translation, X shearing, scaling, Y shearing, filtering, blurring, different kinds of noises, histogram equalization, rotation, etc. Lastly, the proposed technique is compared with state-of-the-art watermarking techniques and their comparison shows significant improvement of proposed scheme over existing techniques.

• 한국통신학회논문지
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• 제24권7B호
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• pp.1378-1383
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• 1999

본 논문에서는 웨이브릿 변환을 이용한 새로운 가변블록 기반 영상압축방식을 제안하였다. 웨이브릿의 각 밴드별로 통계적 특성이 다르므로 각 부밴드에 적합한 양자화기에 적용하였으며, 각 부밴드의 방향특성을 이용하여 부밴드들을 서로 다른 크기의 가변블록으로 겹치지 않게 분해하였다. 또한 에너지의 특성을 고려하여 임계값 이하의 값들은 0으로 보내어 부호화하지 않음으로써 불필요한 비트의 할당을 줄인다. 시뮬레이션 결과 제안알고리즘은 기존의 블록 기반 압축알고리듬에 비해 압축률과 PSNR면에서 객관적으로 향상된 성능을 보였고, 주관적으로도 블록기반 방식임에도 불구하고 매우 낮은 BPP를 갖는 압축에서 나타나는 블록화 현상이 나타나지 않음을 확인하였다. 또한 0의 위치정보를 표현하는 방법에 있어 블록기반으로 접근하기 때문에 간단한 구조를 가지는 장점이 있다.

• 한국정보통신학회논문지
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• 제13권11호
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• pp.2304-2310
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• 2009

본 논문에서는 디지털 통신에서 비트 전송율을 향상시킬 수 있는 웨이브릿 편이 변조 시스템을 제안한다. 기존의 웨이브릿 편이 변조 시스템에서는 스케일링 함수(scaling function)를 1로, 웨이브릿(wavelet)을 0으로 할당하여 0과 1을 구분하였다. 제안한 방식은 스케일링 함수와 웨이브릿 그리고 이 두 신호를 반전시킨 4개의 반송파를 사용하여 변조한다. 즉, 웨이브릿은 00, 반전된 웨이브릿은 01, 스케일링 함수를 10, 반전된 스케일링 함수를 11로 할당하여 비트 전송률을 2배로 향상시키고자 한다. 복조시에는 4개의 상관기를 이용하여 원래의 2진 데이터(2비트)를 복원하였다. 모의실험 결과 제안한 방식이 기존의 웨이브릿 편이 변조 시스템에 비해 전송효율이 2배 향상되었음을 확인하였다.

• 한국항행학회논문지
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• 제20권6호
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• pp.539-543
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• 2016

본 논문은 Daubechies 정상 웨이블릿 변환을 이용하여 무인항공기 항공촬영 영상의 성능을 향상하기 위한 기법에 대해 연구하였다. 무인항공기에서 획득된 영상이 가장 일반적이고 보편적으로 적용되는 가우시안 잡음에 의하여 손상되었을 경우, 영상의 성능을 개선하기 위한 실험을 수행하였다. 정상 웨이블릿 변환은 DWT (discrete wavlet transform)에서 다운샘플링에 의해 발생하는 문제점을 해결하기 위한 변환방법으로써 잡음제거에 DWT보다 효과적이라고 알려져 있다. 또한 Haar 웨이블릿은 불연속 함수인 이유로 매끄러운 신호나 영상처리에 효과적이지 못하다. 이에 본 연구에서는 daubechies 정상 웨이블릿을 이용하여 잡음을 제거하였으며 기존 haar 정상 웨이블릿을 적용하였을 때 보다 더 성능이 개선됨을 확인하였다.

• 한국정보시스템학회지:정보시스템연구
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• 제18권3호
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• pp.351-373
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• 2009

An index fund is a collective investment scheme that aims to replicate the movements of an index of a specific financial market regardless of market conditions. An index fund is a popular investment alternative because it is much cheaper to run than an active fund and it performs better than actively managed funds. This paper illustrates the usefulness of wavelet analysis in constructing an index fund. The wavelet analysis can decompose the time series data in frequency domain as well as in time domain. The major findings of this paper are as follows. First, the beta coefficient that represents the systematic risk has the scale dependent property. This result can provide important information to the investors with various investment time frequency. Investors can use the betas corresponding to their investment frequencies among the various scale betas estimated by wavelet analysis. Second, we can find the usefulness of wavelet analysis in constructing index fund because the wavelet technique gives less tracking error(difference between the index performance and the index fund performance) than the traditional constructing techniques. The result of this study implies that the wavelet techniques can be an important analytic method to the other financial markets such as option market, futures market, bond markets and currency market.

• Earthquakes and Structures
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• 제3권6호
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• pp.839-852
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• 2012

Earthquake records are often analyzed in various earthquake engineering problems, making time-frequency analysis for such records of primary concern. The best tool for such analysis appears to be based on wavelet functions; selection of which is not an easy task and is commonly carried through trial and error process. Furthermore, often a particular wavelet is adopted for analysis of various earthquakes irrespective of record's prime characteristics, e.g. wave's magnitude. A wavelet constructed based on records' characteristics may yield a more accurate solution and more efficient solution procedure in time-frequency analysis. In this study, a low-pass reconstruction filter is obtained for each earthquake record based on multi-resolution decomposition technique; the filter is then assigned to be the normalized version of the last approximation component with respect to its magnitude. The scaling and wavelet functions are computed using two-scale relations. The calculated wavelets are highly efficient in decomposing the original records as compared to other commonly used wavelets such as Daubechies2 wavelet. The method is further advantageous since it enables one to decompose the original record in such a way that a clear time-frequency resolution is obtained.