• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2003.06a
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• pp.226-229
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• 2003

본 논문은 Uncooled DFB-LD를 광원으로 사용하는 일반적인 8채널 구조의 CWDM시스템에 대해 메트로 파장대를 사용하여 최대 15채널까지 증설이 가능한 시스템 구조에 대한 제안 및 특성을 시뮬레이션 하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.7
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• pp.1335-1341
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• 2017

In this paper, a new architecture of multiple conference servers which use extended control channel framework in SIP(session initiation protocol) session has been presented. For this purpose, in this study, a new extended control channel framework architecture which can distribute total conference system loads to multiple servers effectively has been presented. In the implementation, extended control channels have been connected by using SIP sessions that was established between each conference servers, and extended control channel messages which can be transferred through control channels have been designed in this study. These extended control channel messages can distribute system load effectively between multiple conference servers, and conference information data format that can represent extended control channel framework has also been designed. Furthermore, exchange procedures of extended control channel messages have also been presented. The performance of the proposed system has been analysed by simulation. The analysis results show that average SIP messages delay time and average media stream delay time have improved.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.10a
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• pp.611-613
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• 2017

This paper proposes a new method to reduce the overhead by pilots for single carrier frequency domain equalization (SC-FDE) transmission. In the conventional SC-FDE transmission structure, the overhead by transmitting pilot are heavy because the pilot are transmitted at every SC-FDE block. The proposed SC-FDE structure has fewer pilots and many SC-FCE blocks are transmitted between pilots. The channel estimation and equalization is performed at the pilot period and the channels between pilots are estimated through linear interpolation. This reduces the pilot overhead by reducing the pilot transmission compared with the conventional structure, and enables reliable channel estimation and equalization.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.12A
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• pp.1836-1842
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• 2000

이 논문은 레일레이 감쇄 채널 환경에서 IMT-2000 파일럿 심볼 구조의 W-CDMA 시스템 역방향 링크의 채널 추정에 관한 LMS 적용형 알고리즘 성능을 WMSA(Weighted Multi-Slot Averaging)(K=1,2,3), 일정 추정이득 (Constant estimation gain) 및 RLS 알고리즘 성능과 비교 분석하였다. 이 논문의 모형은 IMT-2000 3GPP 규격의 W-CDMA 채널 구조, 변조 및 파일럿 패턴을 이용하였다. 파일럿 심볼 위치의 채널추정은 LMS 알고리즘을 이용하고 데이터 심볼 위치의 채널보상은 선형 보간으로 수행하였다. 저속 도플러 주파수에서는 WMSA(K=1,2,3) 성능이 일정 추정이득, RLS 및 LMS 적응형 알고리즘 성능보다 우수하며, WMSA(K=1) 성능의 경우 일정 추정이득, RLS 및 LMS 적응형 알고리듬 성능과는 큰 차이가 없다. 그리고 LMS 알고리즘 성능은 WMSA(K=1) 성능과 매우 비슷한 결과를 얻었다. 그러나 도플러 주파수가 고속화될수록 LMS 알고리즘의 성능이 WMSA(K=1), 일정 추정이득 및 RLS 알고리즘 성능보다 우수함을 확인하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.10a
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• pp.614-616
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• 2017

In this paper, based on the conventional SC-FDE structure, we propose a new SC-FDE structure to cope with narrow band jammer. In the conventional SC-FDE structure, channel estimation is performed in the time domain. When a narrow band jammer exists, time-domain channel estimation is very difficult due to high power jamming interference, which degrades receiver performance. To relieve from this problem, a new SC-FDE frame is proposed to enable channel estimation under narrow band jamming environments. In this paper, we proposed a modified SC-FDE structure that can perform channel estimation in the frequency domain, and verified the performance via computer simulation.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.5
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• pp.961-971
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• 2019

Isolation between virtual machines in a cloud computing environment is an important security factor. The violation of isolation between virtual machines leads to interferences of shared resources and the implementation of covert channels. In this paper, the structure of Hyper-V hypervisor is analyzed to implement covert channels between virtual machines. Hyper-V uses a mutex technique for mutual exclusion between virtual machines. It indicates that isolation of virtual machines is violated and covert channels can be implemented due to mutex. We implemented several covert channels by designing a method for searching mutex resources applicable to Hyper-V with complex architectures. The mutex-based covert channel is not hardware dependent. If the covert channel is detected or defended, the defensive technique can be avoided by using the other covert channel among several covert channels.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.2 s.43
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• pp.1-8
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• 2007

A flat fluorescent lamp (FFL) was developed as a light source for LCD TV Backlight. The channels of FFL were realized by forming the flat glass at high temperature. The performance of the backlight with FFL was shown to improve by optimizing the FFL channel profile that has elliptical shape, 4.4 mm height and 1.4 mm sealing distance. In this paper, the brightness uniformity of LCD TV backlights was investigated by optical simulation of FFL channel profiles. The brightness of LCD TV using FFL with the optimized channel profile was shown to be $576\;cd/m^2$.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06b
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• pp.72-74
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• 2012

본 논문은 미래 군에서 CR (Cognitive Radio) 기술을 적용한 전투무선망에서의 효율적인 주파수 사용을 위한 정책기반 동적 채널 선정 구조를 제안한다. 전투무선망에서는 상용의 기지국과 같은 Coordinator가 존재하지 않기 때문에 효율적인 채널 사용을 위해서 각 상황마다 어떻게 대응할 것인가에 대한 고려사항이 있다. 이에 대한 해결책으로 정책기반의 동적 채널 선택 구조를 제안하며, 이는 각 상황에 따른 규칙이나 행동을 사전에 정책으로 정의하여 특정 Coordinator가 없더라도 해당 상황이 발생하면 사전 정의된 정책에 의해서 동적 채널 선택을 하는 것이다. 즉, 전투무선망에서 작전상황이나 전술통신환경의 변화에 따라 PU (Primary User)나 SU (Secondary User)를 동적으로 할당하는 것을 의미한다. 모의 실험결과 별도의 정책 없이 Random하게 동적 채널을 선택하는 기존기법보다 정책기반의 기법이 월등한 성능향상을 보였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1732-1743
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• 1998

In this paper, we have proposed a channel assignment shceme for the multiple traffic class environment where the traffic volume varies with time. Our basic idea is to assign radio channels considering the characteristics of each traffic class and mobile speed and change the number of allocated channels for each traffic class according to vaiation of traffic volume. To evalute the perfomance of our proposed algorithms, we conducted analyical and simulation studies. We derived new call blocking probability and hand-off failure probability of the proposed scheme analytically. The simulatioh results show that our proposed algorithms can grantee GOS of each traffic class and provide a fairness between the new call and the hand-off call.

• Journal of Advanced Navigation Technology
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• v.6 no.3
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• pp.203-210
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• 2002

In this paper, the BER performance of IEEE 802.11a OFDM WLAN system is obtained by simulation and it is shown that the proposed modified channel estimation algorithm improves the channel estimation performance of the system. The wireless channel used in channel simulation includes AWGN and delay spread channel implemented by TDL model. At first, the performance of OFDM WLAN system according to data rate and coding rate defined in standard is evaluated in AWGN channel. Then, imperfect channel estimation in indoor wireless channel is considered. After the performance of conventional channel estimation scheme using only two long training symbols is evaluated, and that of proposed modified channel estimation scheme using additional 8 short training symbol is compared with it. From the simulation results, it is shown that modified channel estimation scheme provides reduced channel estimation error and improves the channel estimation performance due to noise averaging effect with the same preamble format as defined in specification.