• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.86-89
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• 2009

In this paper, a broadband power line communication modem and network technology to develop tests with actual characteristics of the underground power line communication channel to be interpreted. Length and structure of the underground distribution line due to underground distribution line to the broadband powerline communication channels to measure the amount of attenuation on the signal generator, spectrum analyzer, such as contactless coupler was used to configure the channel measurement system. Demonstration tests in the test line as a single line by selecting the longest high-voltage lines where the two-channel measurement and signal attenuation on the noise level was measured. Measuring results degrade communication performance can be quite sure that was the presence of impulse noise, long lines, the line length was confirmed by the high-frequency attenuation appears.

• The Journal of the Acoustical Society of Korea
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• v.25 no.8
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• pp.356-361
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• 2006

We present the performance of differential space-time block decoders. which does not require the channel state information. We suggest the structure of the multiple blocks differential space time decoders. which does not require the channel state information, and analyze the Performances. In quasi-static flat fading channels. the Performance of multiple blocks differential detection (MD-STC) outperforms that of 2 blocks(D-STC) by 1.5dB. But in the time-selective fading channels due to Doppler frequency $(f_d)$, the performance of MD-STC degrades as the vehicular speed is greater than 200km/hr in 802.16e systems, where the data transmission rate is 144kbps.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.278-281
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• 2010

협력 통신을 위한 프로토콜로 제안된 Hybrid relaying은 Source로부터 relay로 전송된 정보의 복호 성공 여부에 따라 증폭 후 전송 (AF) 기법과 복호 후 전송 (DF) 기법을 선택적으로 이용하여 전송한다. 최근 초고속 근거리 무선통신을 위한 테라 헤르츠 대역의 반송파를 이용한 연구가 활발해 지면서 Rician fading 채널 기반의 통신 기법 연구들이 중요 해 지고 있다. 본 논문에서는 각 노드간의 채널환경이 Rician fading 으로 모델링 되는 경우에 Hybrid relaying을 이용한 협력통신 기법의 outage probability를 분석한다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.110-118
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• 2007

In multi-hop wireless network, multi-channel makes it possible to enhance network performance because it reduces channel interferences md contentions. Recently several schemes have been proposed in the literatures to use multi-channel. Especially, MCR(Multi channel routing protocol), which utilize hybrid interface assignment, is a prominent routing protocol. MCR uses simple way to change channel but efficiently reduce channel interferences. In this paper, we propose a load-aware channel selection algorithm called LCS that enhances the channel switching algerian used in MCR protocol. In LCS, channel of a node is assigned based on collected information about queue length of neighbors. Moreover this paper evaluates the performance of in by using simulation test and testbed demonstration. Test results show that the MCR with LCS outperforms the naive MCR.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7B
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• pp.632-641
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• 2006

Recently FCC has considered about the unlicensed device operation in licensed bands. However, this operation can give the harmful interference to the existent licensed system while unlicensed devices operate. Therefore, there should be strict requirements to protect licensed system. So in this paper we propose dynamic frequency selection method in the MAC layer, which is based on the cognitive radio technology. The proposed dynamic frequency selection method creates channel lists after sensing the licensed channels. And it helps the CR base station immediately to moves the current channels that are used by the unlicensed system to other available bands dynamically when a licensed system's signal is detected. This method can reduce interference that is caused by unlicensed devices. In addition, it can maximize channel utilization with enabling coexistence of unlicensed system and licensed system.

• The Transactions of the Korea Information Processing Society
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• v.4 no.11
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• pp.2832-2839
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• 1997

In this paper, a testing architecture and procedure that an idle ATM virtual channel can be utilized for TCP channel is proposed. Four kinds or methodologies for protocol conformance testing have been standardized in ISO. Remote testing method used popularly have some disadvantages that developer must operate system manually in case of System Under Test (SUT) active testing and we cannot control and observe Implementation Under Test (IUT) often. It is proper to adopt distribute testing method than remote test in order to maximize test coverage and optimize fault coverage for conformance testing in ATM systems, and it is required that TCP channel is prepared for distribute testing method. The proposed architecture can adopt distributed testing method without extra physical channel for testing control. Also we can maximize the test coverage and implement the automation of testing without intervention of operator sustaining normal operation of ATM equipment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.4
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• pp.318-327
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• 2017

It is essential for the near-field receiving measurement to make beam pattern and check the performance of a active phased array antenna system. Also, we could obtain compensation value for mono-pulse function through the near-field receive test, however, if the radar has many frequency channel, the test would take long time and hard effort. So it is needed that frequency channels are selected for measurement and calculates the values for other frequency channels to improve efficiency in development and manufacture. In this case, the phase variations in sum and del channels would be checked. The phase measurement includes un-linear characteristic because of wrapping effect. Generally, radars have similar path length in sum and del channel, but if a radar has a electrical length gap between sum and del channel, errors could occur by phase's wrapping effect. In this paper, the interpolation method's error caused by electrical length gap is checked and the effective method for frequency channel selection to avoid wrapping effect is introduced.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.59-63
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• 2007

본 논문은 지연 다이버시티를 이용한 초광대역무선통신시스템의 PN 부호 포착 성능을 분석하였다. 무선채널은 주파수 선택적인 로그노말 페이딩 채널로 모델링하였다. 포착 성능은 PN 부호의 불확실한 부분에서 여러 개의 동기 상태가 존재한다는 가정하에서 검파 확률과 평균 포착 시간의 관점에서 분석되었다. 시뮬레이션 결과로부터 지연 다이버시티를 이용한 포착 시스템이 낮은 수신기의 단가와 복잡도에도 불구하고 다이버시티 이득을 획득할 수 있다는 것이 증명되었다. 본 논문의 결과는 CDMA에 기초한 초광대역무선통신시스템의 동기단을 디자인하는데 적용될 수 있다.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11b
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• pp.214-216
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• 2005

디지털 방송이 시작되면서 시청자가 선택할 수 있는 채널은 200여 개로 늘어났다. 지금처럼 리모컨으로 채널을 돌려가며 보거나 원하는 TV 프로그램을 찾기란 거의 불가능해진 것이다. 이러한 다채널 다매체 시대에 원하는 프로그램 시청을 도와줄 수 있는 프로그램 가이드 시스템의 필요성이 증가하게 되었고, 더 나아가 TV를 시청하는 각 개인의 선호도를 반영하는 것이 요구되었다. 본 논문에서는 r-order Markov Model을 이용한 개인화된 전자 TV 프로그램 추천 시스템을 제안한다. Markov Model은 시간이 지남에 따라 시청하는 프로그램의 변화를 모델링하기 위한 방법으로 사용하였다. 이 시스템은 시청자의 선호 프로그램을 예측하기 위해서 r-order Markov Model을 제안하는 것뿐만 아니라 TV 시청자의 프로그램 선호를 예측하기 위한 모델들을 적용하였다. 실험 결과는 Markov Model이 추천에 대한 높은 정확성을 제공할 수 있다는 것을 보여준다.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10c
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• pp.216-218
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• 2000

최근 VoD와 같은 멀티미디어 응용 프로그램에 대한 관심이 증가함에 따라 이에 많은 연구가 진행되고 있는데, 이중에서도 제한적인 네트워크 자원에 적합한 멀티캐스트 전송에 대한 연구가 관심을 끌고 있다. VoD 멀티미디어 응용프로그램은 사용자가 선택한 비디오를 서버가 사용자에게 실시간으로 전송하여 재생하는 것 외에도 일시정지, 재시작, 빨리 감기, 되감기와 같은 VCR 기능을 지원해야 한다. 본 논문에서는 멀티캐스트 환경의 VoD 시스템에서 VCR 기능을 지원하는 방법을 제시하고 있다. 많은 사용자가 비슷한 시기에 VCR 요청을 하는 경우 개별적인 유니캐스트 채널을 통해 서비스하지 않고, 하나의 멀티캐스트 채널을 여러 사용자가 공유하여 서비스 받기 때문에, 제한적인 네트워크 환경에서 효율적인 방식이다.