• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.540-544
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• 2002

본 논문에서는 IEEE802.11a의 규격에 따라 OFDM 무선 LAN 모뎀과 프레임 포맷을 구성하여 시뮬레이션에 의해 BER 성능을 분석하고 수정된 채널 예측 알고리즘을 적용하여 채널예측성능이 개선됨을 보인다. 실내 무선채널로서는 AWGN과 TDL 모델을 적용한 지연확산채널을 고려한다. 우선 AWGN 환경에서 규격에 제시된 전송속도 및 부호율에 따른 OFDM 무선 LAN 시스템의 성능을 분석하고, 다음으로 실내무선채널 환경에서 채널추정이 불완전한 경우에 대한 성능을 분석한다. 기존의 채널추정방식으로서 프리앰블내의 2개의 Long 훈련심볼을 이용하여 채널을 추정하는 경우에 대한 성능을 분석하고, 이를 수정하여 Long 훈련심볼 뿐만 아니라 전체 10개의 Short 훈련심볼 중 8개의 훈련심볼들을 채널추정에 부가적으로 사용하는 방식을 채용한 경우의 성능을 분석하여 기존의 방식과 비교한다. 시뮬레이션 결과에 대한 분석으로부터 수정된 채널추정방식을 적용하는 경우, 잡음을 억제하는 효과가 높아지므로 채널추정오차를 감소시켜서 성능이 개선됨을 확인하였다.

• Journal of the Korea Institute of Military Science and Technology
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• v.5 no.1
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• pp.24-36
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• 2002

It is important to use frequency resource effectively to support much more users, to maximize the DS-CDMA system performance. In this paper, we use MPSK, QAM, MFSK and PR coder as a baseband modulation method for DS-CDMA system. Increasing user's number, we compare the performance of each system using different baseband modulation method, by expecting BER performance. BPSK has generally good performance, in case of low power operation of terminal 8FSK has excellent performance relatively, PR has excellent performance when high power operation of terminal and also good for situation of excessive user's number. QAM is not suitable for DS-CDMA system.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1996.10b
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• pp.104-112
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• 1996

석탄공급방식에 따른 250MW급 석탄가스화 복합발전 플랜트의 성능을 생성가스의 발열량 및 발전 효율의 측면에서 살펴보았다. 대상탄은 Illinois No. 6탄, Drayton탄, Buckskin탄 및 Usibelli탄을 사용하였으며, 각 탄에 대하여 건식 및 습식 석탄 공급 방식에 따른 생성가스 및 정화가스의 조성과 IGCC 플랜트의 성능을 비교하였다. 탄소 함량이 높을수록 발전 효율은 증가하는 경향을 나타내었으며, 습식 석탄공급방식보다는 건식 석탄공급방식이 발전효율면에서 유리한 것으로 나타났다.

• Fire Science and Engineering
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• v.17 no.2
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• pp.56-61
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• 2003

The smoke removal rate from a room with an opening was investigated for different smoke control systems by using the large eddy simulation turbulence model of the Fire Dynamics Simulator. The decreasing rate of the particles randomly distributed in the 2m X 2m X 2.4m room was com-pared for the ventilation system, pressurization system and extraction system, and for the air flowrate of the ventilation system. Difference in the smoke removal rate among the three smoke control systems was small when the opening was closed. The pressurization system showed less smoke removal rate than the other two systems when the opening existed, and hence is not recommended for subway stations with large openings. It was also shown that a less flowrate in the ventilation system leads to a much longer smoke removal time.

• The Journal of the Korea Contents Association
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• v.9 no.5
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• pp.84-90
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• 2009

In this paper, the new channel estimation was proposed that have the low complexity and high performance using Fuzzy inference method uses recently from various field for estimation about uncertainty in channel estimation of OFDM. Proposed method is channel estimation performance improve, calculation and interpolation for statistics character of channel using the pilot before LS channel estimation by Fuzzy inference method. Simulation result in QPSK proposed channel estimation method shows the enhancement of 5.5dB compared to the LS channel estimation and the deterioration of 1.3dB compared to the MMSE channel estimation in mean square error point $10^{-3}$. symbol error rate shows similarity performance the MMSE $10^{-1.96}$, proposed channel estimation $10^{-1.93}$ and enhancement of $10^{-0.35}$ compared to the LS channel estimation in signal to noise ratio point 20dB.

• The Journal of the Acoustical Society of Korea
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• v.19 no.8
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• pp.3-11
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• 2000

This paper considers the performance of a dynamic priority control function (DPCF) of a threshold-based Bernoulli priority jump (TBPJ) scheme. Loss-sensitive and delay-sensitive traffics are applied to a system with a TBPJ scheme that is a general state-dependent Bernoulli scheduling scheme. Loss-sensitive and delay-sensitive traffics represent sound and data, respectively. Under the TBPJ scheme, the first packet of the loss-sensitive traffic buffer goes into the delay-sensitive traffic buffer with Bernoulli probability p according to system states which represent the buffer thresholds and the number of packets waiting for scheduling. Performance analysis shows that TBPJ scheme obtains large performance build-up for the delay-sensitive traffic without performance degradation for the loss-sensitive traffic. TBPJ scheme shows also better performance than that of HOL scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.629-637
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• 2013

Chaos communication systems have the characteristics such as non-periodic, wide-band, non-predictability of signals and easy implementation. There have been many studies about chaos communication systems because of these advantages. But, chaos communication systems have low BER(Bit Error Rate) compare to general digital communication system. Existing researches on chaos communication systems only analyze BER performance according to various chaos maps. There are no studies on analysis of BER performance according to PDF(Probability Density Function) of chaos maps. In this paper, we analyze the BER performance according to changing parameter, equation, and initial values of chaos map's PDF. In addition, we propose new chaos map to improve BER performance. Simulation results show that BER performance of CDSK(Correlation Delay Shift Keying) is changed when PDF of chaos map changed. And the proposed chaos map has a better BER performance compare to previous chaos maps such as Tent map, Logistic map, and Henon map.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.4
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• pp.10-18
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• 2003

In the present study, several different types of PSD performance test systems were reviewed. Basically there are two methods to pulsate the system; whole-feeding-system pulsation and working-fluid pulsation. The latter method adopts either a piston-type pulsator or a restrict-type pulsator The working-fluid pulsation using a restrict-type pulsator was considered to be the most appropriate experimental system to study the effects of the primary parameters, and a practical design of the system was proposed.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.677-681
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• 2003

본 논문에서는 멀티미디어 통신시스템을 위한 적응변조방식을 제안하였으며, 성능개선 기법으로는 Truncated Type-II Hybrid ARQ 방식과 MRC 다이버시티 합성기법을 사용하였다. 적응변조방식은 변조레벨에 의해 조절되고, 심볼 지수는 나카가미 페이딩 파라미터 값에 따라 변화한다. 멀티미디어 통신 시스템의 성능 해석은 다중 사용자 상황에서 적응변조방식 만을 고려한 경우, 적응변조방식과 Truncated Type-II Hybrid ARQ 방식을 고려한 경우와 적응변조방식에 Truncated Type-II Hybrid ARQ 방식과 최대비합성 다이버시티 합성기법을 동시에 고려한 경우를 비교 분석한다.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.241-243
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• 2002

본 논문은 무선 랜 상에서 전송 지연을 보장하기 위한 백오프 방식을 제안한다. 이 방식은 전송되는 트래픽의 종류에 따라 백오프 시간을 할당하도록 설계되었으며, 기존의 IEEE 802.11 매체접근제어 방식을 그대로 유지하며, 보다 향상된 서비스 품질을 지원한다. 제안된 백오프 방식에서는 모든 트래픽을 실시간 트래픽과 비실시간 트래픽으로 구분하여 처리된다. 실시간 트래픽은 제안된 백오프 방식으로 처리되고, 비실시간 트래픽은 기존의 IEEE 802.11 방식에 의해 처리된다. 본 논문에서는 컴퓨터 시뮬레이션을 사용하여 제안된 백오프 방식을 성능 평가하였으며, 시뮬레이션 결과는 전송지연 관점에서 기존의 IEEE 802.11e 방식보다 성능이 향상됨을 보여준다.