• Journal of Korea Society of Industrial Information Systems
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• v.14 no.4
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• pp.8-15
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• 2009

Relay-assisted multi-input multi-output (MIMO) technique has become a promising candidate for next generation broadband wireless communications for high speed access. In this paper, we propose channel selective relay-based MIMO transmission system. The performance of relay-based system can be improved by using the subcarriers selectively based on the channel condition between relay and mobile station. Simulation results show that the proposed relay-based system considerably outperforms the conventional relay-based system.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.05a
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• pp.95-98
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• 2008

본 논문은 기존의 질감기반 (texture) 얼굴검출 시스템에서 컬러 영상을 도입하여 성능개선의 중요한 부분인 얼굴 오검출율을 줄이는 방법을 제안한다. 얼굴 영상의 컬러 성분은 흑백 성분과 비교하여 낮은 공간 주파수 영역을 가지는 특징이 있다. 질감기반 얼굴검출에서 높은 대비 (contrast) 성분의 에지는 얼굴이 아닌 영역에서 얼굴로 오인할 수가 있다. 본 논문에서는 이런 오인을 감소하기 위해 독립적인 컬러 채널 성분들을 질감기반 얼굴 검출에 각각 이용하여 그 얻어진 결과들을 융합 (fusion) 하는 방법을 제안한다. 실험결과로 제안한 칼라 채널 융합 방법을 통해 얻은 얼굴 검출율은 기존 흑백 영상과 비슷하게 유지되며 오검출율을 현저히 줄이는 것을 보였다.

• The KIPS Transactions:PartB
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• v.9B no.3
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• pp.351-358
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• 2002

Video compression based on DCT (Discrete Cosine Transform) has weakpoints of blocking artifacts and pixel loss when the resolution is changed. DWT (Discrete Wavelet Transform) based method can overcome such problems. In SAMCoW (Scalable Adaptive Motion Compensation Wavelet), one of wavelet based video coding algorithm, both intra frames and motion compensated error frames are encoded using EZW(Embedded Zerotree Wavelet) algorithm. However the property of wavelets transform coefficients of motion compensated error frames are different from that of still images. Signal energy is not highly concentrated in the lower bands which is true for most still image cases. Signal energy is rather evenly distributed over all frequency bands. This paper suggests a new video coding algorithm utilizing these properties. Spatial band coding which is known to be very effective for encoding images with relative1y high frequency components and not utilizing the interband coefficients correlation is applied instead of EZW to encode both intra and inter frames. In spatial band coding, the position and value of significant wavelet coefficients in each band are progressively transmitted. Unlike EZW, inter band coefficients correlations are not utilized in spatial band coding. It has been shown that spatial band coding gives better performance than EZW when applied to wavelet based video compression.

• Tunnel and Underground Space
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• v.19 no.1
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• pp.19-30
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• 2009

For the purpose of determining the thickness of concrete lining and detect of the cavity where may be located behind tunnel lining, IE (Impact-Echo) method it effectively useful in the tunnel safety diagnosis and the quality control during the construction. As a part of case study, we applied IE method to various tunnel structure types such as road tunnel and subway tunnel constructed by NATM (New Austrian Tunnelling Method) and ASSM (American Steel Support Method). As tunnel specifications estimated from this method were compared with coring data, design drawing and other survey results, it was very good agreement with each other. In conclusion, we verified that IE method shows an accurate and reliable result. The conventional interpretation of IE method in frequency domain gives only vertical information at a certain point. However, the interpretation using time-frequency analysis and depth section imaging technique from two dimensional profiling surveys can show more reliable information about structure inside.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.3
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• pp.48-55
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• 2008

This paper presents a design of a multi-band infernal antenna for mobile handsets which can cover the major mobile services such as WiBro/WiMAX mobile internet services and Media-FLO/S-DMB services. Using wideband monopole antenna structure, the proposed antenna obtains the wide bandwidth characteristic at high Sequency band to be applicable for new mobile services. Stacking meandered radiator on the wideband monopole radiator and obtaining the different current path and lenga on these stacked radiators, overall antenna volume is effectively reduced. The measured bandwidths (VSWR<3) of the proposed antenna is 270 MHz and 2032 MHz at low and high band, respectively. This antenna can effectively covers major wireless communication bands including Media-FLO, CDMA, GSM, GPS, DCS, PCS, UMTS, WiBro, WiMAX, and S-DMB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.8
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• pp.857-863
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• 2014

In determining interaction between plasma and electromagnetic wave, plasma frequency and collision frequency are two key parameters. They are derived from electron density and temperature, which vary in an extremely wide range, depending on a plasma generator. Because the parameters are usually unknown, traditional researches have utilized simplified electron density model and constant electron temperature approximation. Introduction of plasma fluid model to electromagnetics is suggested to utilize relatively precise time dependent variables for given generator. Dielectric barrier discharge(DBD) generator is selected due to its simple geometry which allows us to use one dimensional analysis. Time dependent property is analyzed when microwave is launched toward parallel plate DBD plasma. Afterwards, attenuation tendency with the change of electron density and temperature is demonstrated.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.2
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• pp.10-17
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• 1999

This paper investigates the linear stability of both uniform and non-uniform density plane mixing layers with special emphasis on the effect of the wake component in the velocity profile. Velocity and density profiles for laminar flows are obtained from analytic profiles. Mixing layers with wakes have two generalized inflection points and two unstable modes-sinuous and varicose modes. For uniform density mixing layers, sinuous modes are more unstable than varicose modes, which shows wakes will be destabilized by sinuous modes. For non-uniform density mixing layers with high density in high speed flows, sinuous modes are more unstable than varicose modes. For non-uniform density mixing layers with high density in low speed flows, varicose modes can be more unstable than sinuous modes.

• Journal of Aerospace System Engineering
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• v.14 no.5
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• pp.1-8
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• 2020

The aeroservoelastic analysis that deals with the interactions of the inertial, elastic, and aerodynamic forces and the influence of the control system have been performed. MSC Nastran was used for the free vibration analysis of the structure model as the pre-analysis. ZAERO was used to calculate the unsteady aerodynamic forces. The unsteady aerodynamic forces were verified by comparing with Doublet Hybrid Method. Karpel's Minimum-State Approximation method was used for approximation of the aerodynamic forces to the Laplace domain in the frequency domain. The aeroservoelastic state-space equation was obtained by combining the aeroelastic equation with the actuator dynamics. The analysis of aeroservoelastic stability concerning the elevator input of the high aspect ratio model was performed. The root-locus method and time-integration method were used for the analysis of aeroservoelastic in frequency and time domain.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.237-240
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• 2000

본 연구에서는 한국 동해 대륙붕 해역에서의 주요 해양현상인 수직 수온구조의 단기변동, 수온전선, 그리고 내부파의 변동을 분석하고 이들 변화에 따른 음파의 음장변화를 고찰하였다. 한국 동해항 근해에서 수온의 수직적 변화는 계절적인 변화 이외에 약 2주간의 짧은 기간에도 매우 극적인 변화가 존재함이 실측자료를 통해 밝혀졌다. 1999년 관측된 CTD 자료를 바탕으로 음장 변화를 살펴본 결과 주파수 1kHz, 음원수심 $30{\cal}m$ 인 경우 수신기 수심에 따라 최소 3dB, 최대 10dB까지 차이를 가져올 수 있음을 알 수 있었다. 한국 동해에서 연안과 외해 사이에는 수온전선이 매우 자주 발달하며 여름에 가장 강한 것으로 알려져 있다. 동해항 근해에는 대표적인 수괴인 대마난류수와 북한한류수가 공존하며 이들의 상대적인 세력 변화 때문에 수은(음속)이 거리에 따라 급격하게 변하는 수온전선이 발달할 수 있다. 저주파수 대역 (200Hz)에 대한 간단한 시뮬레이션 결과는 수온전선이 정상적인 분포에 비해서 거리에 따라 7dB 정도의 큰 전파손실을 초래할 수 있음을 보인다. 한국 동해 연안에도 내부파가 존재한다는 사실이 최근 3년간의 연구 결과 밝혀졌다. 내부파는 외해에서 발생하여 대륙단을 거쳐 대륙붕으로 진행해 오면서 내부파 군 (Packets)으로 분산된다. 수직적 변화가 전체 수층의 $14\%$를 차지하는 간단한 형태의 내부파를 가정하여 음장변화를 시물레이션 한 결과 주파수 1 kHz, 음원수심 $20{\cal}m$인 경우 내부파는 수렴구역 형성을 현저하게 방해하여 최대 5dB까지의 차이를 유발하였다. 추후 이에 대한 연구는 내부파 전체의 시,공간적 분포 특성이 구체적으로 규명되면 보다 정확한 음장변화 추정이 이뤄져야 할 것으로 보인다. 또한 내부파와 음파의 상대적인 진행 방향에 따라 음장변화가 크게 다를 것이 예상되므로 이를 규명하기 위해서는 궁극적으로 3차원적인 음장분포 연구가 필요하다. 음향센서를 해저면에 매설할 경우 수충의 수온변화와 센서 주변의 수온변화 사이에는 어느 정도의 시간지연이 존재하게 되므로 이에 대한 영향을 규명하는 것도 센서의 성능예측을 위해서 필요하리라 사료된다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.1
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• pp.95-101
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• 2009

Wireless Sensor Network (WSN) has limited power and bandwidth. In order to high data rate and high speed communication systems are required. Cooperative communication system can help to decrease power consumption through spatial diversity. In cooperative transmission, one partner node assists one sensor node to transmit their data to destination. Instead of using M partners for M sensor nodes, we propose 1 partner for M sensor nodes. And we proposed relay selection scheme base on ARQ. Proposed protocol offers higher diversity order as conventional one with much less bandwidth and power. The destination will consider the one packets received from the best relay to reduce the complexity of the system. We verified BER performance for the proposed protocol through Monte-Carlo simulation over Rayleigh fading plus AWGN.