• 한국정보통신학회논문지
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• 제5권7호
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• pp.1346-1353
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• 2001

본 논문에서는 2차원 분모분리형 디지털 필터의 선계에 대한 알고리즘을 제안한다. 제안된 알고리즘은 진폭 특성과 위상특성으로 주어진 2차원 디지털 필터의 주파수 영역 설계명세조건을 특이치 분해를 이용하여 1차원 디지털 필터의 설계명세조건으로 분해한다. 따라서, 2차원 디지털 필터 설계문제는 1차원 디지털 필터의 설계 문제로 귀착되며 이는 계산적으로 유효하며 수치적으로 안정한 설계법으로 고려되며 설계 예로부터 유효성을 확인한다.

• 한국정보통신학회논문지
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• 제4권2호
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• pp.407-416
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• 2000

본 논문은 트리구조의 필터뱅크를 이용하여 필터링을 할 때 데시메이션으로 인해서 생기는 왜곡을 보상하기 위해서 보조 필터(엘리어싱 제거기)를 사용하는 방법을 제안하고 이를 이용하여 잡음을 제거하여 음질을 향상시키는 실험을 행했다. 입력신호는 두 채널의 분석필터에 의해 서브밴드로 분해된 후 데시메이션되고 다시 각 서브밴드로 분해된 신호를 적응필터를 이용하여 필터링을 한다. 이러한 기법으로 각 주파수 대역을 균일한 대역으로 분해할 수 있으며 각 서브밴드별로 각기 다른 수렴상수를 사용할 수 있어서 수렴속도를 향상시킬 수 있는 장점이 있다. 특히 잡음 제거나 음질 향상에 서브밴드 적응 필터뱅크를 응용할 경우 수렴속도가 빨라야 하며, 임펄스 응답의 길이가 긴 시스템을 모델링하는 데 응용할 수 있는 장점이 있다. 적응필터 계수의 갱신 방법으로는 VSS(Variable Step Size) LMS 알고리듬을 사용하였으며, 실험 결과, 기존의 서브밴드 구조보다 제안한 구조가 최소 평균 오차나 수렴성능 면에서 우수한 성능을 보였다.

• 대한전자공학회논문지SP
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• 제44권6호
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• pp.93-99
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• 2007

본 논문에서는 ${\alpha}$-stable 확률분포를 갖는 잡음에 열화된 이미지의 화질을 개선하는 알고리즘을 제안한다. 제안한 진폭제한 평균필터(amplitude-limited sample average filter)는 heavy-tailed 가우시안 잡음환경 하에서 maximum likelihood estimator (MLE)임을 증명한다. 그리고, 이 알고리즘에 해당하는 error norm은 Huber의 minimax norm과 일치하고, 위에서 언급한 잡음 환경 하에서 efficacy를 최대화한다는 점에서 최적의 필터임을 보인다. 이 개념을 미리어드(myriad) 필터와 결합하여 진폭제한 미리어드 필터(amplitude-limited myriad filter)를 제안하고 실험을 통하여 이의 성능을 확인한다.

• 전기학회논문지P
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• 제64권2호
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• pp.67-73
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• 2015

Distance relay is widely used for the protection of long transmission line. Most of distance relay used to calculate line impedance by measuring voltage and current using DFT. So if there is a computation error due to the influence of phasor by DC offset component, due to excessive vibration by measuring line impedance, overreach or underreach can be occurs, and then abnormal and non-operation of distance relay can be issue. It is very important to implement the robust distance relaying that is not affected by DC offset component. This paper describes an enhanced distance relaying based on the DC offset elimination filter to minimize the effects of DC offset on a long transmission line. The proposed DC offset elimination filter has not need any prior information. The phase angle delay of the proposed DC offset filter did not occurred and the gain error was not found. The enhanced distance relay uses fault current as well as residual current. The behavior of the proposed distance relaying using off-line simulation has been verified using data about several fault conditions generated by the ATP simulation software.

• 한국가시화정보학회지
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• 제17권2호
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• pp.48-57
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• 2019

A straightforward strategy for particle image velocimetry (PIV) interrogation and post-processing has been proposed, aiming at reducing errors and clarifying vortex structures. The interrogation window size should be kept small to reduce bias error and improve spatial resolution. A spatial filter is then applied to the velocity field to reduce random error and clarify flow structure. The performance of three popular spatial filters were assessed: box filter, median filter, and local quadratic polynomial regression filter. In order to quantify random uncertainty, the image matching (IM) method is applied to an experimental dataset of homogeneous and isotropic turbulence (HIT) obtained by 2D-PIV. We statistically analyze the uncertainty propagation through the spatial filters, and verify the reduction in random uncertainty. Moreover, we illustrate that the spatial filters help clarify vortex structures using vortex identification criteria. As a result, PIV random uncertainty was reduced and the vortex structures became clearer by spatial filtering.

• 제어로봇시스템학회논문지
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• 제7권8호
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• pp.703-710
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• 2001

The nonlinear observers are proposed for a nonlinear system. To improve the characteristics such as stability, convergence, and $H^{\infty}$ filter performance criterion, we utilize an $H^{\infty}$ filter Riccati equation or a modified $H^{\infty}$ filter Riccati equation with a freedom parameter. Using the Lyapunov function method, the characteristics of the observers are analyzed. Then the in-flight alignment for a strapdown inertial navigation system(SDINS) is designed using the proposed observer. And the additive quaternion error model is especially used to reduce the uncertainty of the SDINS error model. Simulation results show that the observer with the modified $H^{\infty}$ filter Riccati equation effectively improves the performance of the in-flight alignment.

• 한국군사과학기술학회지
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• 제9권1호
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• pp.5-12
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• 2006

This study describes an SDINS/GPS/ZUPT integration algorithm for land navigation systems. The SDINS error can be decoupled in two parts. The first part is the the Schuler component which does not depend on object motion parameters, and the other is the Non-Schuler part which depends on the product of object acceleration and azimuth error. Azimuth error causes SDINS error in proportion to the traversed distance. The proposed system consists of a GPS/SDINS integration system and an SDINS/ZUPT integration system, which are both realized by an indirect feedforward Kalman filter. The main difference between the two is whether the estimate includes the Non-Schuler error or not, which is decided by the measurement type. Consequently, subtracting GPS/SDINS outputs from SDINS/ZUPT outputs provide the Non-Schuler error information which can be applied to improving azimuth accuracy. Simulation results using the raw data obtained from a van test attest that the proposed SDINS/GPS/ZUPT system is capable of providing azimuth improvement.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2023년도 학술발표회
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• pp.25-25
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• 2023

The ensemble optimal interpolation (EnOI) scheme is a sub-optimal alternative to the ensemble Kalman filter (EnKF) with a reduced computational demand making it potentially more suitable for operational applications. Since only one model is integrated forward instead of an ensemble of model realizations, online estimation of the background error covariance matrix is not possible in the EnOI scheme. In this study, we investigate two Gaussian noise based ensemble generation strategies to produce dynamic covariance matrices for assimilation of water level observations into a distributed hydrological model. In the first approach, spatially correlated noise, sampled from a normal distribution with a fixed fractional error parameter (which controls its standard deviation), is added to the model forecast state vector to prepare the ensembles. In the second method, we use an adaptive error estimation technique based on the innovation diagnostics to estimate this error parameter within the assimilation framework. The results from a real and a set of synthetic experiments indicate that the EnOI scheme can provide better results when an optimal EnKF is not identified, but performs worse than the ensemble filter when the true error characteristics are known. Furthermore, while the adaptive approach is able to reduce the sensitivity to the fractional error parameter affecting the first (non-adaptive) approach, results are usually worse at ungauged locations with the former.

• 제어로봇시스템학회논문지
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• 제17권1호
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• pp.31-37
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• 2011

Recently gantry-type robot with 3 axes rectangular coordinates have been studied in the many industrial production equipment and machinery fields. To acquire a good handling and motion performance of this robot, reducing the settling-time and securing the accurate-transfer positioning under high-speed conditions should be required. However when robot is moved in high-speed, the large inertia of robot can lead to serious vibration of robot's head. The time-delayed control characteristics of this robot can also lead to tracking error. In this research, the analysis of the effects of higher order positional-profile is carried out to assure high-speed performance and stiffness specifications. To remove the residual vibration caused by kinematic coupling effect of dual-servo gantry, we develop a dual-servo gantry of rotary type that moving frame of x-axis rotates about z-axis. In order to decrease the tracking error, the 3 type lead-filter through system identification was applied respectively. From the experimental results, it was shown that zero-order series leader-filter has the best performance about tracking error and settling time.

• 제어로봇시스템학회논문지
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• 제17권12호
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• pp.1183-1187
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• 2011

In this paper, an optimal FIR (Finite-Impulse-Response) filter is proposed for discrete time-varying state-space models. The proposed filter estimates the current state using measured output samples on the recent time horizon so that the variance of the estimation error is minimized. It is designed to be linear, unbiased, with an FIR structure, and is independent of any state information. Due to its FIR structure, the proposed filter is believed to be robust for modeling uncertainty or numerical errors than other IIR filters, such as the Kalman filter. For a general system with system and measurement noise, the proposed filter is derived without any artificial assumptions such as the nonsingular assumption of the system matrix A and any infinite covariance of the initial state. A numerical example show that the proposed FIR filter has better performance than the Kalman filter based on the IIR (Infinite- Impulse-Response) structure when modeling uncertainties exist.