• 한국통신학회논문지
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• 제35권6C호
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• pp.516-522
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• 2010

본 논문에서는 중국향 휴대이동방송인 CMMB(China multimedia mobile broadcasting)를 위한 소수배 주파수 동기와 정수배 주파수 오차 추정 알고리듬을 제안한다. 제안한 소수배 주파수 동기 알고리듬은 CMMB의 프레임 구조에 가장 적합하도록 전치부호를 활용하여 매 CMMB 심볼마다 추정이 가능하다. 또한 제안된 정수배 주파수 알고리듬은 CMMB 동기 신호를 이용하여 매 프레임마다 추정 한다. 제안 알고리듬은 시간 오프셋이 존재할 때에도 소수배와 정수배 주파수 오프셋을 정확히 추정할 수 있으며 다중 경로 상황에서도 우수한 성능을 보인다.

• 응용통계연구
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• 제29권3호
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• pp.463-470
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• 2016

주파수 영역에서 시계열 자료를 분석함에 있어 스펙트럴 추정량은 매우 유용한 도구이다. 기존의 스펙트럴 추정량은 이상치에 영향을 받을 수밖에 없는 구조로 되어있어서 M-추정법을 활용하여 로버스트 스펙트럴 추정량이 제안되었다. M-추정을 위해서는 조율모수를 적절하게 선택해 주어야 하는데 Pak (2001)이 제안한 방법을 사용할 때의 효과를 연구하였다. 모의실험과 주택가격지수에의 적용을 통하여 효과가 있음을 확인하였다.

• Journal of Power Electronics
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• 제15권2호
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• pp.419-430
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• 2015

Flux estimation is a significant foundation of high-performance control for DC-excited synchronous motor. For almost all flux estimators, such as the flux estimator based on phase locked loop (PLL), DC drift causes fluctuations in flux magnitude. Furthermore, significant dynamic error may be introduced at transient conditions. To overcome these problems, this paper proposes an improved flux estimator for the PLL-based algorithm. Filters based on the generalized integrator are used to avoid flux fluctuation problems caused by the DC drift at the back electromotive force. Programmable low-pass filters are employed to improve the dynamic performance of the flux estimator, and the cutoff frequency of the filter is determined by the dynamic factor. The algorithm is verified by a 960V/1.6MW industrial prototype. Simulation and experimental results show that the proposed estimator can estimate the flux more accurately than the PLL-based algorithm in a cycloconverter-fed DC-excited synchronous machine vector control system.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 I
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• pp.234-237
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• 2003

The accuracy of channel estimation significantly affects the performance of coherent OFDM receiver. It is desirable to employ a good channel estimator while requiring low implementation complexity. In this paper, we propose a channel estimator that employs a simple two-dimensional (2-D) moving average (MA) filter as the channel estimation filter. The optimum tap size of the 2-D MA FIR filter is analytically designed in the time and frequency domain in association with the channel condition and pilot signal to interference power ratio. The analytic results can be applied to the design of adaptive channel estimator. Finally, the performance of the proposed channel estimator is verified by computer simulation.

• Journal of Communications and Networks
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• 제15권5호
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• pp.496-503
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• 2013

In an orthogonal frequency division multiplexing system, conventional interpolation techniques cannot correctly balance performance and overhead when estimating dynamic long-delay channels in single frequency networks (SFNs). In this study, classical filter analysis and design methods are employed to derive a complex interpolator for maximizing the resistible echo delay in a channel estimator on the basis of the correlation between frequency domain interpolating and time domain windowing. The coefficient computation of the complex interpolator requires a key parameter, i.e., channel length, which is obtained in the frequency domain with a tentative estimation scheme having low implementation complexity. The proposed complex adaptive interpolator is verified in a simulated digital video broadcasting for terrestrial/handheld receiver. The simulation results indicate that the designed channel estimator can not only handle SFN echoes with more than $200{\mu}s$ delay but also achieve a bit-error rate performance close to the optimum minimum mean square error method, which significantly outperforms conventional channel estimation methods, while preserving a low implementation cost in a short-delay channel.

• 한국통신학회논문지
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• 제36권7C호
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• pp.481-487
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• 2011

CDD(Cyclic Delay Diversity)는 다중 전송 안테나를 사용하는 OFDM(Orthogonal Frequency Division Multiplexing) 시스템에서 간단히 전송 다이버시티를 얻을 수 있는 기법이다. 그러나 CDD 안테나가 적용된 OFDM 시스템에서 형성되는 채널의 주파수 선택적 특성은 정수배 주파수 옵셋(Integer Frequency Offset)과 FFT(Fast Fourier Transform) 이후의 동기화 기법들의 성능 감쇄를 발생시킨다. 본 논문은 CDD를 갖는 OFDM 기반의 DRM+ 시스템을 위한 향상된 정수배 주파수 옵셋 추정 기법을 제안한다. 제안된 기법에서는 채널의 주파수 특성이 동일한 파일롯 부분 집합을 선택함으로써 CDD에 형성되는 채널의 주파수 선택적 특성에 의한 정수배 주파수 옵셋 추정의 열화 성능을 감소시킨다. 모의실험 결과를 통해 제안된 기법의 정수배 주파수 옵셋 추정 성능이 기존 기법에 비해 향상됨을 보인다.

• 제어로봇시스템학회논문지
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• 제14권5호
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• pp.415-419
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• 2008

Detecting and correcting defects on LCD glasses early in the manufacturing process becomes important for panel makers to reduce the manufacturing costs and to improve productivity. Many attempts have been made and were successfully applied to detect and identify simple defects such as scratches, dents, and foreign objects on glasses. However, it is still difficult to robustly detect low-contrast defect region, called Mura or blemish area on glasses. Typically, these defect areas are roughly defined as relatively large, several millimeters of diameter, and relatively dark and/or bright region of low Signal-to-Noise Ratio (SNR) against background of low-frequency signal. The aim of this article is to present a robust algorithm to segment these blemish defects. Early 90's, a highly robust estimator, known as the Model-Fitting (MF) estimator was developed by X. Zhuang et. al. and have been successfully used in many computer vision application. Compared to the conventional Least-Square (LS) estimator the MF estimator can successfully estimate model parameters from a dataset of contaminated Gaussian mixture. Such a noise model is defined as a regular white Gaussian noise model with probability $1-\varepsilon$ plus an outlier process with probability $varepsilon$. In the sense of robust estimation, the blemish defect in images can be considered as being a group of outliers in the process of estimating image background model parameters. The algorithm developed in this paper uses a modified MF estimator to robustly estimate the background model and as a by-product to segment the blemish defects, the outliers.

• 전자공학회논문지
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• 제50권4호
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• pp.212-218
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• 2013

본 논문에서는 위상지연필터를 이용한 리니어 모터 피스톤 진폭 추정기를 구현하였다. 리니어 컴프레서가 적용된 냉장고나 에어컨의 냉각능력을 제어하기 위해서는 단위시간동안 피스톤의 움직인 거리, 즉 피스톤의 속도를 제어해야 하는데 이때 리니어 모터의 주파수나 스트로크를 조정함으로써 가능하다. 이때, 주파수를 고정하고 스트로크를 변화시키는 것이 일반적이다. 스트로크, 즉 피스톤 진폭을 정확하게 추정하는 것이 리니어 컴프레서의 동특성을 좌우하는데, 본 연구에서는 위상지연필터를 이용한 피스톤 진폭 추정기를 제안하고 성능이 우수함을 모의실험을 통해 확인하였다.

• Communications for Statistical Applications and Methods
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• 제23권5호
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• pp.411-421
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• 2016

Large frequency limiting distributions of two errors in realized covariance are investigated under noisy and non-synchronous high frequency sampling situations. The first distribution characterizes increased variance of the realized covariance due to noise for large frequency and the second distribution characterizes decreased variance of the realized covariance due to discretization for large frequency. The distribution of the combined error enables us to determine the sampling frequency which depends on a nuisance parameter. A consistent estimator of the nuisance parameter is proposed.

• Journal of the Korean Data and Information Science Society
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• 제14권4호
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• pp.837-844
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• 2003

In this paper, we obtain the estimator of system reliability for the bivariate Pareto model with bivariate type 1 censored data. We obtain the estimators and approximated confidence intervals of the reliability for the parallel system based on likelihood function and the relative frequency, respectively. Also we present a numerical example by giving a data set which is generated by computer.