• Journal of Korea Multimedia Society
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• v.21 no.2
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• pp.108-116
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• 2018

In this paper, we propose an image enhancement method based on Multi-Scale Retinex theory that designs Unsharp Masking Filter (UMF) and emphasizes the contrast ratio adaptively. Unsharp Masking (UM) technique emphasizes image sharpness and improves contrast ratio by adding high frequency component to the original image. The high frequency component is obtained by differentiating between original image and low frequency image. In this paper, we present how to design an UMF kernel and to adaptively apply it to increase the contrast ratio according to multi-scale retinex theory which resembles human visual system. Experimental results show that the proposed method has better quantitative performance indexes such as PSNR, ambe & SSIM and better qualitative feature like halo artifact suppression.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.154-159
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• 2004

Numerical simulations of supersonic impinging jet flows are carried out using the axisymmetric Navier-Stokes code. This paper focuses on the oscillatory flow features associated with the variation of the nozzle pressure ratio and nozzle-to-plate distance. Frequencies of the surface pressure oscillation from computational results are in accord with the measured impinging tones for various cases of nozzle-to-plate distance. The variation of this frequency with distance show a staging behavior. Computed results for the case of nozzle pressure ratio variation for a fixed nozzle-to-plate distance also demonstrate a staging behavior. These two seemingly different staging behaviors are found to obey the same frequency-distance characteristics when the frequency and the distance are normalized by using the length of the shock cell.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.3
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• pp.352-357
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• 2008

We present a space-time trellis coded OFDM system in slow fading channels. Generalized principal ratio combining (GPRC) is also analyzed theoretically in frequency domain. The analysis shows that the decoding metric of GPRC includes the metrics of maximum likelihood(ML) and PRC. The computer simulations with M-PSK modulation are obtained in frequency flat and frequency selective fading channels. The decoding complexity and simulation running times are also evaluated among the decoding schemes.

• Journal of electromagnetic engineering and science
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• v.7 no.4
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• pp.195-200
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• 2007

Doubly-selective channel estimator for orthogonal frequency division multiplexing(OFDM) systems is proposed in this paper. Based on the generalized complex exponential basis expansion model(GCE-BEM), we describe the time-variant channel with time-invariant coefficients over multiple OFDM blocks. The time variation of the channel destroys the orthogonality between subcarriers, and the resulting channel matrix in the frequency domain is no longer diagonal, but the main interference comes from the near subcarriers. Based on this, we propose a channel estimator with low pilot ratio. We first develop a least-square(LS) estimator under the assumption that only the maximum Doppler frequency and the channel order are known at the receiver, and then verify that the correlation matrix of inter-channel interference(ICI) is a scaled identity matrix based on which we derive an optimal pilot insertion scheme for the LS estimator in the sense of minimum mean square error. The proposed estimator has the advantages of low pilot ratio and robustness against inter-carrier interference.

• Journal of Multimedia Information System
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• v.4 no.2
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• pp.65-73
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• 2017

This paper proposes a method to improve the image quality by designing Unsharp Mask Filter (UMF) based on Retinex theory which controls the frequency pass characteristics adaptively. Conventional unsharp masking technique uses blurring image to emphasize sharpness of image. Unsharp Masking(UM) adjusts the original image and sigma to obtain a high frequency component to be emphasized by the difference between the blurred image and the high frequency component to the original image, thereby improving the contrast ratio of the image. In this paper, we design a Unsharp Mask Filter(UMF) that can process the contrast ratio improvement method of Unsharp Masking(UM) technique with one filtering. We adaptively process the contrast ratio improvement using Unsharp Mask Filter(UMF). We propose a method based on Retinex theory for adaptive processing. For adaptive filtering, we control the weights of Unsharp Mask Filter(UMF) based on the human visual system and output more effective results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.337-343
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• 2012

NREL(National Renewable Energy Laboratory) Baseline controller conduct using method proposed RISO National Laboratory in Region 3. which designed the blade-pitch control system using a single degree-of-freedom model of the wind turbine. Idealized PID-Controlled rotor-speed error will respond as a second-order system with the natural frequency and damping ratio. RISO proposed specific natural frequency(=0.6 rad/s) and damping ratio(=0.7). If specific Eigen value apply to NREL 5 MW wind turbine, differ with pitch respond for simulation results of RISO report. Variation of specific eigen value investigate performance of NREL 5 MW wind turbine.

• Journal of electromagnetic engineering and science
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• v.13 no.2
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• pp.104-112
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• 2013

A novel miniaturized artificial magnetic conductor (AMC) is proposed for dual-band operation. An AMC unit cell that employs four slots in the metallic patch is used to achieve miniaturization as well as easy control of the second/first resonant frequency ratio, which can be varied from 1.5 to 3.26 by simply changing the slot shape for a given metallic patch size. A dual-band antenna composed of a wideband monopole suspended over the proposed AMC surface is designed and tested to validate this approach. The measurements result in a satisfactory and good matching condition for the dual-band antenna.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.5
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• pp.806-808
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• 2015

In this paper, we suggest the method of pilot tone design for a compressed channel sensing in order to decrease the peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems.

• Journal of Communications and Networks
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• v.11 no.3
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• pp.229-239
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• 2009

Orthogonal frequency division multiplexing (OFDM) has been adopted as a standard for various high data rate wireless communication systems due to the spectral bandwidth efficiency, robustness to frequency selective fading channels, etc. However, implementation of the OFDM system entails several difficulties. One of the major drawbacks is the high peak-to-average power ratio (PAPR), which results in intercarrier interference, high out-of-band radiation, and bit error rate performance degradation, mainly due to the nonlinearity of the high power amplifier. This paper reviews the conventional PAPR reduction schemes and their modifications for achieving the low computational complexity required for practical implementation in wireless communication systems.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.1
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• pp.81-85
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• 1996

Microwave dielectric properties of 0.15(B $a_{x}$S $r_{0.05}$)O-0.15(S $m_{2}$(1-y)N $d_{2y}$) $O_{3}$-0.7Ti $o_{2}$(x=o.9~0.1[mol.], y=6[m/o]) ceramics were investigated with BaO compositional ratio. Sintered density and resistivity of specimens were independent on the BaO compositional ratio. In the specimen with x=0.975[mol.], dielectric constant, quality factor and temperature coefficient of resonant frequency had good values of 76.52, 3001(at 3[GHz]) and +0.71[ppm/.ceg. C], respectively. By comparing with the stoichiometric compositions of 78.14, 2938(at 3[GHz])+14.19[ppm/.ceg. C], dielectric constant and quality factor showed similar properties, but the temperature coefficient of resonant frequency was highly improved. (author). refs., figs., tabs.s.s.