• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권9호
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• pp.4240-4258
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• 2016

A practical iterative channel estimation technique is proposed for the multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system in the high-speed mobile environment, such as high speed railway scenario. In the iterative algorithm, the Kalman filter and data detection are jointed to estimate the time-varying channel, where the detection error is considered as part of the noise in the Kalman recursion in each iteration to reduce the effect of the detection error propagation. Moreover, the employed Kalman filter is from the canonical state space model, which does not include the parameters of the autoregressive (AR) model, so the proposed method does not need to estimate the parameters of AR model, whose accuracy affects the convergence speed. Simulation results show that the proposed method is robust to the fast time-varying channel, and it can obtain more gains compared with the available methods.

• 대한전자공학회논문지TC
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• 제38권4호
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• pp.11-17
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• 2001

본 논문에서는 High-Order QAM(Quandrature Amplitude Modulation)을 적용하는 모뎀에서 강인하고 넓은 범위의 주파수 포착 범위를 가지는 극성판단(Polarity Decision) 반송파 동기용 PD(Phase Detector) 알고리즘을 제안하고 이에 대한 평균 출력특성(S-curve)과 분산특성을 수학적으로 유도하여 기존의 DD(Decision Directed)방식과 비교 분석한다. 기존의 DD 방식의 선형영역은 256 QAM의 경우 $3.5^{\circ}{\sim}3.5^{\circ}$ 이었으나 제안한 알고리즘의 선형영역은 ${\gamma}-17.9$에서 $36^{\circ}{\sim}36^{\circ}$ 의 넓은 구간을 가진다. 또한 기존의 DD 방식에서는 256 QAM의 주파수 오프셋 포착 성능이 ${\pm}10\;KHz$ 이하였다. 이는 아날로그 front-end 회로에서 주파수 오프셋이 일반적으로 ${\pm}100\;KHz$ 정도까지 줄어들 수 잇는 것을 감안하면 AFC(Automatic Frequency Control) 또는 반송파 복구를 위한 보조적인 위상검출회로가 필요하게 됨을 의미한다. 그러나 제안된 극성판단 반송파 동기 알고리즘을 사용하면 보조적인 회로의 도움없이 SNR = 30 dB에서 최대 ${\pm}300\;KHz$의 주파수 오프셋까지도 포착 가능하다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2005년도 공동학술대회 논문집
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• pp.273-280
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• 2005

MT 전달함수의 추정과정에서 로버스트 방법의 적용은 현재 전자탐사 분야에서 일반적이다. 적절하게 고안되고 적용된 로버스트 방법은 출력 채널인 전기장에 포함되어 있는 외치의 영향을 감소시킬 수 있으나, HLP(High leverage point)라 불리 우는 자기장(입력 채널)의 외치에 종종 민감하지 못하다. 이 문제를 해결하기 위해 HLP의 영향을 최소화할 수 있는 BI(Bounded Influence) 추정이 제안되었고, 전통적인 로버스트 방법보다 신뢰성 있는 전달함수를 제공하는 것으로 보고되었다. 이는 BI 추정이 M-추정을 적용함과 동시에 자기장 성분만으로 결정되는 모자행렬의 통계적인 특성을 고려하여 가중치를 부여하는 방법이기 때문이다. 본 연구에서는 전달함수 추정과정에 BI 추정을 적용하고, 이와 더불어 전처리 단계로서 전자기장의 통계적 분포를 이용해 주파수 영역에서 극단적인 전기장과 자기장 자료의 영향을 감소시키는 기법을 개발하였다. 개발된 전처리 기법은 BI 추정으로 제거될 수 없는 자료를 주파수 영역에서 효과적으로 제거하는 것으로 생각된다. 본 연구에서 개발된 기법의 효율성과 장점은 합성 자료와 현장 자료를 이용하여 도시될 것이다.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제7권2호
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• pp.143-147
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• 2007

This paper proposes a new watermarking scheme in which a logo watermark is embedded into the discrete wavelet transform (DWT) domain of the original image using exact radial basis function neural networks (RBF). RBF will learn the characteristics of the image, and then watermark is embedded and extracted by the trained RBF. A watermark is added to the coefficients at the low frequency band of the DWT of an image and a watermark is embedded into the DWT domain using the trained RBF. The trained RBF also used in watermark extracting process. Experimental results show that the proposed method has good imperceptibility and high robustness to common image processing attacks.

• 전기학회논문지
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• 제62권4호
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• pp.444-450
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• 2013

This paper presents the criteria for setting the dynamic operating mode of BESS(Battery Energy Storage System) in the bulk power systems. ESS has been expected to improve the degraded dynamic performance of the power system with high penetration of the renewable resources. While ESS is controlled in steady state or dynamic operating mode for its better effectiveness depending on the operating conditions of power systems, the criteria for setting the dynamic operating mode for the transient period needs to be robust enough to cover all the different conditions. The proposed criteria consider the varying conditions and the operating practices of the bulk power systems.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 Proceedings of the Korea Automatic Control Conference, 11th (KACC); Pohang, Korea; 24-26 Oct. 1996
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• pp.16-19
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• 1996

In this paper, a sliding mode control scheme that guarantees the smoothness of the control signal and the exponential error convergence is proposed for robot manipulators. The proposed method inserts a low pass filter (LPF) in front of the plant, and the virtual controller is designed for the virtual plant - the combination of the LPF and the robot manipulator. The virtual control signal contains high frequency components because of a switching function. The real control signal, however, always shows a smooth curve since it is an output of the LPF. In addition to the smoothness of the control signal is always assured, the overall system is in the sliding mode at all times, that is, its performance is always invariant under the existence of parameter uncertainties and external disturbances. The closed-loop system is shown to be globally exponentially stable.

• Structural Monitoring and Maintenance
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• 제3권4호
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• pp.395-406
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• 2016

Modal parameter identification has received much attention recently for their usefulness in earthquake engineering, damage detection and structural health monitoring. The identification method based on Matrix Pencil technique is adopted in this paper to identify structural modal parameters, such as natural frequencies, damping ratios and modal shapes using impulse vibration responses. This method can also be applied to dynamic responses induced by stationary and white-noise inputs since the auto- and cross-correlation function of the two outputs has the same form as the impulse response dynamic functions. Matrix Pencil method is very robust to noise contained in the measurement data. It has a lower variance of estimates of the parameters of interest than the Polynomial Method, and is also computationally more efficient. The numerical simulation results show that this technique can identify modal parameters accurately even if the noise level is high.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 학술대회 논문집 정보 및 제어부문
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• pp.487-489
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• 2004

As the electrodes are not needed, the electrodeless lamps using the induction discharge have a long lifetime and are robust against the variable output condition of a ballast. This paper proposed a dimmable resonant inverter for the electrodeless lamps. The proposed resonant inverter formed a half bridge inverter adopted FWM to control the average output power of the inverter and the illumination of a lamp. In this paper, the proposed dimming algorithm was described and the prototype experimental setup for 100W electrodeless lamps was carried out to verify the validity of the proposed dimming method.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.293-298
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• 1993

In ground vehicles, the increasing demand for safety and ride comfort which are trade-off relation, especially at high speeds, has led to the development od actively controlled suspensions. The LQG/LTR controller can be used to design a robust feedback control system that deals with disturbance rejection properties as well as insensitivity to modelling errors and sensor noise. And when the disturbance can not be measured but is limited within a certain frequency range, a bandpass feedback to eliminate the disturbance response can be used. In this paper, hybrid controller cosisted of bandpass feedback controller and LQG/LTR controller is applied to a quarter-car model moving on a randomly profiled road. The random road profile considered as colored noise is shaped from white noise by use of shaping filter. The performance of the hybrid control system is compared with that of an LQG/LTR controlled system.

• 한국위성정보통신학회논문지
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• 제12권4호
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• pp.166-169
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• 2017

This paper describes atmospheric phenomena and effects for satellite-to-ground laser communication channel. Satellite laser communication has advantages such as very high bandwidth, inherent security, robustness to electromagnetic interference, unlicensed frequency band. However, satellite laser communication is affected by various factors. Transmission quality is degraded by factors as system loss, geometric loss, misalignment loss, atmospheric loss. Atmospheric loss is major factor of performance degradation. In this paper, the atmospheric phenomena such as absorption, scattering and turbulence are discussed and analyzed for developing satellite laser channel model and laser transmission scheme robust to atmospheric phenomena.