• 대한수학회지
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• 제52권5호
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• pp.1069-1096
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• 2015

In this article we introduce a numerical method, named Gegenbauer wavelets method, which is derived from conventional Gegenbauer polynomials, for solving fractional initial and boundary value problems. The operational matrices are derived and utilized to reduce the linear fractional differential equation to a system of algebraic equations. We perform the convergence analysis for the Gegenbauer wavelets method. We also combine Gegenbauer wavelets operational matrix method with quasilinearization technique for solving fractional nonlinear differential equation. Quasilinearization technique is used to discretize the nonlinear fractional ordinary differential equation and then the Gegenbauer wavelet method is applied to discretized fractional ordinary differential equations. In each iteration of quasilinearization technique, solution is updated by the Gegenbauer wavelet method. Numerical examples are provided to illustrate the efficiency and accuracy of the methods.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -2
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• pp.868-871
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• 2002

Nowadays, zerotrees based digital watermarking techniques are considered to be an efficient watermarking technique used for multimedia data in a compressed form. This paper presents a technique for watermarking an image, by employing zerotrees derived from the wavelet packet coefficients of the transformed image to carry the watermark signal. By setting a proper threshold in zerotrees determining process, the watermark signal can be recovered without the need of original image. With our proposed technique, more amount of watermark signal can be embedded within the image, compared to ordinary wavelet transform based techniques. The experimental results show the improved performance in both qualities of the resultant watermarked image and robustness of the embedded watermark signal against common signal processing such as brightness/contrast enhancement, high-pass filtering, Gaussian noise adding and JPEG compression scheme

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.97-103
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• 2006

A modified one-sided measurement technique is proposed for Rayleigh wave (R-wave) velocity measurement in concrete. The scattering from heterogeneity may affect the waveforms of R-waves in concrete, which may make the R-waves dispersive. Conventional one-sided techniques do not consider the scattering dispersion of R-waves in concrete. In this study, the maximum energy arrival concept is adopted to determine the wave velocity by employing its continuous wavelet transform. Experimental study was performed to show the effectiveness of the proposed method. The present method is applied to monitor the strength development of early-age concrete. A series of experiments were performed on early-age concrete specimens with various curing conditions. Results reveal that the proposed method can be effectively used to measure the R-wave velocity in concrete structures and to monitor the strength development of early-age concrete.

• 전기학회논문지
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• 제56권12호
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• pp.2251-2256
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• 2007

In this paper, the wavelet transform based lossless image compression algorithm is proposed. The proposed algorithm transforms the input image using 9/7 ICFB and S+P filter, and eliminates the spacious correlation of the subband coefficients, applying the context modeling predictive technique based on the multi-resolution structure and the feedback of the prediction error. The prediction context exploits the subordination and direction property of the different level subband in the vertical, horizontal, and diagonal subband coefficients. The simulation result of the high frequency images such as PEPPERS, BOAT, and AIRPLANE shows that the proposed algorithm efficiently predicts the edge area of each multi-resolution subband.

• International Journal of Aeronautical and Space Sciences
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• 제7권1호
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• pp.73-83
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• 2006

In this paper, a redundancy management system for aircraft is studied, and fault detection and isolation algorithms of inertial sensor system are proposed. Contrary to the conventional aircraft systems, UAV system cannot allow triple or quadruple hardware redundancy due to the limitations on space and weight. In the UAV system with dual sensors, it is very difficult to identify the faulty sensor. Also, conventional fault detection and isolation (FDI) method cannot isolate multiple faults in a triple redundancy system. In this paper, two FDI techniques are proposed. First, hardware based FDI technique is proposed, which combines a parity equation approach with a wavelet based technique. Second, analytic FDI technique based on the Kalman filter is proposed, which is a model-based FDI method utilizing the threshold value and the confirmation time. To provide the reference value for detecting the fault, residuals are calculated using the extended Kalman filter. To verify the effectiveness of the proposed FDI methods, numerical simulations are performed.

• 대한전기학회논문지:시스템및제어부문D
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• 제53권6호
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• pp.433-439
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• 2004

The Helicopter Simulator System is non-linear and complex. Futhermore, because of absence of its accurate mathematical model, it is difficult to control accurately its attitudes such as elevation angle and azimuth one. Therefore, we proposed a Hybrid GA-PID WAVENET(Genetic Algorithm Proportional Integral Derivative Wavelet Neural Network)control technique to control efficiently these angles. The proposed Hybrid GA-PID WAVENET is made through the following process. First, the WAVENET fundamental functions are defined. And their dilation and translation values are adjusted by GA to construct the optimal WAVENET controller. Secondly, the proportional, integral, and derivative gain coefficients of PR controller are tuned optimally. Finally, WAVENET controller which has a good transient characteristic and GA-PE controller which has a good steady state characteristic is adequately combined in hybrid type. Through the computer simulations, it is proved that the Hybrid GA-PE WAVENET control technique has a more excellent dynamic response than PID control technique and GA-PID one.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.169-172
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• 2008

Land-use or land-cover classification of satellite images is one of the important tasks in remote sensing application and many researchers have been tried to enhance classification accuracy. Previous studies show that the classification technique based on wavelet transform is more effective than that of traditional techniques based on original pixel values, especially in complicated imagery. Various wavelets can be used in wavelet transform. Wavelets are used as basis functions in representing other functions, like sinusoidal function in Fourier analysis. In these days, some basis functions such as Haar, Daubechies, Coiflets and Symlets are mainly used in 2D image processing. Selecting adequate wavelet is very important because different results could be obtained according to the type of basis function in classification. However, it is not easy to choose the basis function which is effective to improve classification accuracy. In this study, we computed the wavelet coefficients of satellite image using 10 different basis functions, and then classified test image. After evaluating classification results, we tried to ascertain which basis function is the most effective for image classification. We also tried to see if the optimum basis function is decided by energy parameter before classifying the image using all basis function. The energy parameter of signal is the sum of the squares of wavelet coefficients. The energy parameter is calculated by sub-bands after the wavelet decomposition and the energy parameter of each sub-band can be a favorable feature of texture. The decision of optimum basis function using energy parameter in the wavelet based image classification is expected to be helpful for saving time and improving classification accuracy effectively.

• 한국정보통신학회논문지
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• 제14권5호
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• pp.1155-1163
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• 2010

기존의 웨이브릿 편이 변조 시스템은 스케일링 함수(scaling function)를 1로, 웨이브릿(wavelet)을 0으로 하는 1비트 변조방법이 있고, 스케일링 함수와 웨이브릿 그리고 이 두 신호를 반전시켜서 생성된 4개의 반송파를 사용하는 2비트 변조방법이 있다. 본 논문에서는 2비트 변조방법인 4-ary 스케일링 웨이브릿 편이변조(4-ary SWSK : 4-ary scaling wavelet shift keying) 시스템을 정의하고, QPSK 시스템으로부터 정의된 시스템의 비트 에러 확률과 부호 에러 확률을 유도한다. 제안한 4-ary SWSK 성능을 분석하기 위하여, 기존의 QPSK(quadrature phase shift keying), MFSK(M-ary frequency shift keying), 그리고 제안한 방법의 비트 에러 확률 및 부호 에러 확률을 구한다. 실험결과 제안한 방법의 비트 에러 확률과 부호 에러 확률이 좋은 성능을 보였다.

• 한국항해항만학회지
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• 제32권10호
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• pp.777-783
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• 2008

입자영상속도계(PIV)의 해석에 웨이블릿 변환을 적용하여 정성적인 유동정보뿐만 아니라 공간분해능을 갖는 정량적인 속도장 정보를 제공하고 있다 이 기법은 기포유동(bubbly flow)과 같은 다상(multi-phase)의 유동구조를 해석하는 데도 유용하게 살일 수 있다. 본 연구에서는 기체와 액체의 이상유동(two-pase flow)에 PIV기법을 적용하고 이산 웨이블릿 변환을 사용하여 유장해석을 수행함으로써, 기포를 포함한 속도장 특성과 유동특성을 조사한다.

• 인터넷정보학회논문지
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• 제4권3호
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• pp.39-46
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• 2003

일반적으로 디지털 영상의 저작권 보호를 위한 기존의 워터마킹 기법들은 기하학적 왜곡에 약할 뿐 아니라 왜곡의 정도에 관계없이 모든 워터마크 추출에 동일한 시간을 요구한다. 본 논문에서는 이러한 문제를 해결하기 위하여 콤플렉스 웨이블릿 변환을 이용한 점진적 워터마킹 기법을 제안한다. 제안한 점진적 워터마킹 기법은 원 영상을 콤플렉스 웨이블릿 변환하여 위상 성분에 워터마크를 삽입하며 워터마크가 삽입된 영상으로부터 단계적으로 워터마크를 추출한다. 추출된 워터마크와 원 워터마크의 상관관계를 비교하여 임계값이상이면 영상에 대한 저작권을 주장할 수 있다. 또한 단계적 워터마크의 추출은 왜곡의 정도와 왜곡정도에 따른 워터마크의 추출시간을 결정할 수 있게 한다. 성능평가를 통하여 본 논문에서 제안한 기법이 기존 웨이블릿 변환 기법보다 기하학적 왜곡에 강함을 증명하였다.