• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제12권7호
• /
• pp.3268-3283
• /
• 2018

With the advent of the Information Age, the source identification of digital images, as a part of digital image forensics, has attracted increasing attention. Therefore, an effective technique to identify the source of digital images is urgently needed at this stage. In this paper, first, we study and implement some previous work on image source identification based on sensor pattern noise, such as the Lukas method, principal component analysis method and the random subspace method. Second, to extract a purer sensor pattern noise, we propose a sample selection method to improve the random subspace method. By analyzing the image texture feature, we select a patch with less complexity to extract more reliable sensor pattern noise, which improves the accuracy of identification. Finally, experiment results reveal that the proposed sample selection method can extract a purer sensor pattern noise, which further improves the accuracy of image source identification. At the same time, this approach is less complicated than the deep learning models and is close to the most advanced performance.

• 한국전자파학회논문지
• /
• 제12권5호
• /
• pp.694-704
• /
• 2001

본 논문에서는 상세화된 빔 패턴에 대한 제한조건들은 유지한 채 잡음이나 간섭신호에 대한 효과적인 제거를 제공하는 Eigencanceller의 성능을 평가하였다. Eigencanceller는 배열입력으로 간섭신호와 잡음이 수신되는 경우와 희망신호, 간섭신호 그리고 잡음이 수신되는 경우에 따라 제한조건들이 달라지게 되고 최적의 가중치에 대한 해도 달라진다. 각각의 경우에 가중치 벡터에 대한 정상상태에서의 분석을 통해서 희망 신호의 유.무에 관계없이 최적의 가중치 벡터에 대한 식들은 모두 동일하게 간섭신호에 직교하는 부분공간(subspace)으로의 희망신호의 사영의 형태로 간략화 됨을 알 수 있었다. 그리고 Eigencanceller구조가 DMI(direct matrix inversion)방식보다도 우수한 성능을 보임을 수학적인 분석가 시뮬레이션을 통해 살펴보았다.

• 한국전자파학회논문지
• /
• 제15권9호
• /
• pp.848-855
• /
• 2004

본 논문에서는 긴 코드 DS/CDMA DMB 하향링크 시스템에서의 신호공간에 기초한 새로운 채널추정기법을 제안한다. 신호공간과 잡음공간과의 직교성을 이용하는 종래의 부분공간 방식과는 달리 신호공간만을 이용하여 채널응답을 추정할 수 있다. 신호공간만을 이용하므로 제안된 기법은 종래의 부분공간 방식에서의 연산복잡도 문제를 해결할 수 있고 따라서 실제 구현 가능한 적절한 사이즈의 공분산 행렬로 부분공간 분석을 통한 채널추정기법에 사용될 수 있다. 논문을 통하여 제안된 기법과 관련된 수식을 도출하고 시뮬레이션 및 수치결과를 통해 제안된 기법의 유효성을 보인다.

• Structural Monitoring and Maintenance
• /
• 제4권4호
• /
• pp.331-350
• /
• 2017

Based on the alternative stabilization diagram by varying the time lag parameter in the stochastic subspace identification analysis, this study aims to investigate the measurements from several cases of civil structures for extending the applicability of a recently noticed criterion to ensure stable identification results. Such a criterion demands the time lag parameter to be no less than a critical threshold determined by the ratio of the sampling rate to the fundamental system frequency and is firstly validated for its applications with single measurements from stay cables, bridge decks, and buildings. As for multiple measurements, it is found that the predicted threshold works well for the cases of stay cables and buildings, but makes an evident overestimation for the case of bridge decks. This discrepancy is further explained by the fact that the deck vibrations are induced by multiple excitations independently coming from the passing traffic. The cable vibration signals covering the sensor locations close to both the deck and pylon ends of a cable-stayed bridge provide convincing evidences to testify this important discovery.

• 한국생산제조학회지
• /
• 제24권3호
• /
• pp.327-333
• /
• 2015

As industrial robots come into wider use, their control techniques are being developed along with enhancements in their performance. Specially, the dynamic performance of a 6-axis articulated industrial robot is greatly changed according to the position and orientation of the robot. This means that the PI parameter tuning of the robot and orientation of the robot. This mconsidering the dynamic characteristics of robot mechanism. In this study, $LabView^{(R)}$ programming was applied to automatically conduct parameter scheduling for various robot motions. Using forward and inverse kinematics of RS2, we can divide the working envelope of RS2 into 24 subspaces. We then conduct the gain-tuning according to each subspace. Finally, we program the actual gain scheduling, in which the optimized gain-tuning for each subspace to be passed should be changed for various robot motions using $LabView^{(R)}$.

• 대한수학회지
• /
• 제45권5호
• /
• pp.1443-1482
• /
• 2008

In this paper we define a Myller configuration in a Finsler space and use some special configurations to obtain results about Finsler subspaces. Let $F^{n}$ = (M,F) be a Finsler space, with M a real, differentiable manifold of dimension n. Using the pull back bundle $({\pi}^{*}TM,\tilde{\pi},\widetilde{TM})$ of the tangent bundle $(TM,{\pi},M)$ by the mapping $\tilde{\pi}={\pi}/TM$ and the Cartan Finsler connection of a Finsler space, we obtain an orthonormal frame of sections of ${\pi}^{*}TM$ along a regular curve in $\widetilde{TM}$ and a system of invariants, geometrically associated to the Myller configuration. The fundamental equations are written in a very simple form and we prove a fundamental theorem. Important lines in a Finsler subspace are defined like special lines in a Myller configuration, geometrically associated to the subspace: auto parallels, lines of curvature, asymptotes. Torse forming vector fields with respect to the Cartan Finsler connection are characterized by means of the invariants of the Frenet frame of a versor field along a curve, and the new notion of torse forming vector fields in the sense of Myller is introduced. The particular cases of concurrence and parallelism in the sense of Myller are completely studied, for vector fields from the distribution $T^m$ of the Myller configuration and also from the normal distribution $T^p$.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제6권4호
• /
• pp.1063-1075
• /
• 2012

To locate an object accurately in the wireless sensor networks, the distance measure based on time-delay plays an important role. In this paper, we propose a maximum likelihood (ML) time-delay estimation algorithm in multi-path wireless propagation channel. We get the joint probability density function after sampling the frequency domain response of the multi-path channel, which could be obtained by the vector network analyzer. Based on the ML criterion, the time-delay values of different paths are estimated. Considering the ML function is non-linear with respect to the multi-path time-delays, we first obtain the coarse values of different paths using the subspace fitting algorithm, then take them as an initial point, and finally get the ML time-delay estimation values with the pattern searching optimization method. The simulation results show that although the ML estimation variance could not reach the Cramer-Rao lower bounds (CRLB), its performance is superior to that of subspace fitting algorithm, and could be seen as a fine algorithm.

• Structural Engineering and Mechanics
• /
• 제50권1호
• /
• pp.19-36
• /
• 2014

This paper focuses on a model order reduction (MOR) for large-scale rotordynamic systems by using finite element discretization. Typical rotor-bearing systems consist of a rotor, built-on parts, and a support system. These systems require careful consideration in their dynamic analysis modeling because they include unsymmetrical stiffness, localized nonproportional damping, and frequency-dependent gyroscopic effects. Because of this complex geometry, the finite element model under consideration may have a very large number of degrees of freedom. Thus, the repeated dynamic analyses used to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to complete within a practical design cycle. In this study, we demonstrate that a Krylov subspace-based MOR via moment matching significantly speeds up the rotordynamic analyses needed to check the whirling frequencies and critical speeds of large rotor systems. This approach is very efficient, because it is possible to repeat the dynamic simulation with the help of a reduced system by changing the operating rotational speed, which can be preserved as a parameter in the process of model reduction. Two examples of rotordynamic systems show that the suggested MOR provides a significant reduction in computational cost for a Campbell diagram analysis, while maintaining accuracy comparable to that of the original systems.

• 한국지능시스템학회논문지
• /
• 제21권5호
• /
• pp.569-574
• /
• 2011

이 논문에서는 마이크로어레이 데이터에 대한 분석 문제로서 부공간 대조집단 식별 문제를 소개하고, 이를 해결하는 방법을 제안한다. 제안한 방법은 부공간에서 속성값이 대조적인 집단의 쌍들을 식별하기 위해, 먼저 각 속성에 대해서 분석자가 지정한 대조영역의 값을 갖는 두 개의 샘플집단을 선택한 다음, 연관규칙 마이닝과 유사한 형태의 방법으로 부공간의 차원을 점진적으로 확대해 가면서 대조집단을 추출한다. 마이크로어레이 데이터는 수천개 이상의 유전자에 대한 발현정보를 포함할 수 있는 다차원 데이터이기 때문에, 대조적인 발현특성을 갖는 유전자집합에 대한 샘플집단의 쌍을 모두 부차원에 대해서 질의를 통해 식별하는 것은 부담이 되지만, 제안한 방법을 사용하면 분석자가 지정한 대조영역 값의 범위를 기준으로 하여 모든 가능한 부공간에서의 대조집단을 효과적으로 추출할 수 있다.

• 한국통신학회논문지
• /
• 제35권1A호
• /
• pp.54-61
• /
• 2010

본 논문에서는 셀룰러 환경에서 셀 간 간섭을 완화시키기 위한 부분공간 간섭 정렬 방법을 실제 시스템에 적용할 때 발생하는 채널 분리 오차와 채널 추정 오차에 따른 성능 열화를 개선시키기 위한 수신단 직교화를 통한 간섭 정렬 방법을 제안하였다. 제안된 방법은 셀 마다 서로 직교하는 참조 벡터를 사용함으로써 채널 분리 오차와 채널 추정 오차에 인해 남아있는 간섭신호를 줄여준다. 전산 모의 실험을 통해 채널 추정 오차가 발생하는 환경에서 제안된 방법을 통해 기존의 방법에 비해 향상된 합용량을 얻을 수 있었다.