• 한국전자거래학회지
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• 제2권1호
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• pp.131-151
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• 1997

The CALS/EC is the world-wide accepted concept and its application domain is being expanded continuously throughout the private and public sectors. One of the essential points for realization of CALS/EC is to promote the domestic system integration(SI) industry. This paper describes the present status of the domestic SI companies and the clues to solve their facing problems. In order to evaluate the status of the current SI technology, the MBNQA(Malcom Baldridge National Quality Award) is adopted. The surveyed results show that the average levels of 14 SI companies over 7 evaluation criteria turn out to be 30% through 40% point. The major projects' activities of the SI companies on the information systems over the areas of trade, science and technology, industrial manpower, health and welfare, national security, etc are explained. Also, the competitive power of the SI companies is also discussed. As a target sample, the Korea Telecom(KT) CALS model project is described in terms of its Progresses and Problems. Furthermore, the strategic plans and detailed research items are proposed to resolve on-going issues.

• 한국통신학회논문지
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• 제34권5A호
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• pp.421-428
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• 2009

Inter-cell coordination has been an emerging issue for mitigating inter-cell interference in broadband wireless access networks such as IEEE802.16 and 3GPP LTE (Long Term Evolution). This paper proposes uplink/downlink hybrid inter-cell coordination patterns for a TDD (Time Division Duplex)/MC-CDMA (Multi-Carrier Code Division Multiple Access) system. For the performance analysis, closed forms of inter-cell interferences are derived when uplink and downlink transmissions coexist over a multi-cell environment. In the analysis, we find an optimal ratio of downlink transmit powers of BSs (Base Stations) based on the target outage probability and the performance according to ratios of uplink/downlink transmit powers of MSs (Mobile Stations)/BSs is explored. Our numerical results show that interference mitigation utilizing the characteristics of the uplink and downlink power ratio is very effective in improving system performance in terms of QoS.

• 전자공학회논문지S
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• 제34S권6호
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• pp.46-57
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• 1997

In this paper, we propose an efficient algorithm for adaptation of tracking windwo, which improves tracking performance of a correlation-based video tracker by rejecting background effect originated from a time-varying target. Th eproposed adaptation algorithm ajdusts the size of a tracking window by using the ratio of spatial gradient power in target region to that in backgorund region, which is especially adequate for a correlation-based tracker. Experimental results for synthetic and real image sequences show that the proposed method adapts a tracking window well to a time-varying target and so greatly suppresses background effect, which makes improvement of trakcing performance.

• Current Optics and Photonics
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• 제2권3호
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• pp.215-220
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• 2018

A novel porous-core hexagonal lattice photonic crystal fiber (PCF) is designed and analyzed for efficient terahertz (THz) wave propagation. The finite element method based Comsol v4.2 software is used for numerical analysis of the proposed fiber. A perfectly matched layer boundary condition is used to characterize the guiding properties. Rectangular air-holes are used inside the core to introduce asymmetry for attaining high birefringence. By intentionally rotating the rectangular air holes of porous core structure, an ultrahigh birefringence of 0.045 and low effective material loss of $0.086cm^{-1}$ can be obtained at the operating frequency of 0.85 THz. Moreover, single-mode properties, power fraction in air core and confinement loss of the proposed PCF are also analyzed. This is expected to be useful for wideband imaging and telecom applications.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2005년도 하계학술대회
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• pp.128-132
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• 2005

각종 신호의 디지털 전송에서 Modulation기법에 의해 발생되는 PAPR(Peak to Average Power Ratio)은 전송 신호의 선형성을 보장하기 위하여 고출력 증폭기의 Back-off를 요구하게 된다. 이러한 고출력 증폭기의 Back-off요구로 인하여 원하는 출력에 비해 높은 전력소모량이 필요하여 대출력을 요구하는 장비의 소형화는 크게 제한을 받게 된다. 본 논문에서는 PAR을 감소하기 위한 CFR(Crest Factor Reduction)기법을 위성 DMB용 Gap Filler에 적용하여 장비 크기를 소형화한 사례에 대해 소개한다. 전송신호의 품질에 대한 영향을 최소화 하면서 PAR을 감소하기 위한 방안을 위해 도입된 Simulation 결과와 CFR기법을 적용한 장비에 대한 성능시험 결과 및 필드 테스트 결과에 대해 소개한다.

• 한국항행학회논문지
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• 제6권4호
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• pp.279-290
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• 2002

본 논문에서는 하나의 입력과 다수의 출력을 가지는 [10]에서 제시한 평면 Taper형의 전력 분배/결합기를 2 GHz 대역에서 수정한 구조를 제안한다. 제안하는 구조의 전기적 특성을 결정하는 파라메터들을 HFSS 시뮬레이션을 이용하여 분석하였다. 입력 정합 그리고 각 출력 단에서 출력 신호의 균형과 위상의 선형성을 위해 회로의 중앙에 하나의 원형 모양을 에칭 제거하였다. 또 본 논문에서 제안한 구조의 1:2와 1:3 전력 분배/결합기와 [10]의 구조와 S-Parameter를 비교 분석하였다. 결과적으로 본 연구에서 제시하는 수정된 형태를 적용할 경우 기존의 전력 분배/결합기의 반사손실 특성이 2 GHz에서 20 dB 이상 개선되었고, 대역폭 또한 증가되는 것을 확인하였다.

• 전력전자학회논문지
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• 제18권2호
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• pp.131-137
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• 2013

In this paper, the phase-shift full-bridge DC/DC converter with fixed-phase operation inverter is proposed. The proposed circuit consists of two full-bridge inverters which are connected in parallel. While one full-bridge inverter operates as the fixed-phase, it regulates the output voltage by adjusting the phase of the other inverter. During the normal operation period, the proposed circuit makes the less amount of conduction loss of the primary switches and secondary synchronous rectifiers, as well as the less amount of the current ripple of the output inductor, than the conventional phase-shift full-bridge DC/DC converter does. Also, it achieves high efficiency by reducing the snubber loss of the secondary synchronous rectifier. To sum up, the present inquiry analyzes the theoretical characteristics of the proposed circuit, and shows the experimental results from a prototype for 450W power supply.

• 한국항행학회논문지
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• 제14권5호
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• pp.684-690
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• 2010

차세대 이동통신 시스템은 다양한 서비스의 융합과 멀티모드를 지원하기 위한 구조로 연구되고 있다. 또한 다양한 서비스를 제공받기 위한 사용자의 요구는 점차 증가되고 있으며, 서비스 지원을 위한 대용량 데이터 전송을 위한 많은 통신방식들이 출현하고 있다. 그 중 대표적인 시스템으로 OFDM(Orthogonal Frequency Division Multiplexing) 방식을 이용하는 WiBro(Wireless Broadband), WLAN(Wireless Local Area Network) 등이 있다. 하지만 차세대 이동통신 시스템에서는 하나의 단말로 OFDM 방식을 이용한 통신방식 이외 CDMA(Code Division Multiple Access), WCDMA(Wideband CDMA) 방식을 동시에 지원 받고자한다. 통합된 시스템은 SoC(System on Chip) 기술 적용으로 빠른 발전을 이루고 있지만, 무선통신 시스템에서 필수적으로 요구되는 요소 중 전력 증폭기의 비선형 특성으로 인한 신호의 왜곡을 유발시켜 인접채널 간섭을 성화 시키고 시스템의 효율을 떨어뜨리는 문제를 해결해야 한다. 전력증폭기의 문제점을 해결하기 위해 많은 선형화 기법들이 제시되었으며, 다항식 사전왜곡 기법은 증폭기로 입력되는 신호가 증폭기의 역 특성을 갖도록 하는 기법으로 다항식을 통하여 증폭기를 모델링하기 때문에 수렴 속도가 빠르고 다른 기법들과 비교하여 우수한 성능을 보인다. 본 논문에서는 차세대 이동통신 서비스를 위한 모뎀 구조를 제시하고 OFDM 방식 사용에 있어 발생 되는 PAPR(Peak-to-Average Power Ratio) 감소 기법을 적용한 후 다항식 사전왜곡 기법을 적용하여 차세대 이동통신 시스템을 분석하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권4호
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• pp.1520-1542
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• 2020

Traditional software testing typically uses many physical resources to manually build various test environments, resulting in high resource costs and long test time due to limited resources, especially for small enterprises. Cloud computing can provide sufficient low-cost virtual resources to alleviate these problems through the virtualization of physical resources. However, the provision of various test environments and services for implementing software testing rapidly and conveniently based on cloud computing is challenging. This paper proposes a multilayer cloud testing model based on cloud computing and implements a hybrid cloud testing system based on virtual machines (VMs) and networks. This system realizes the automatic and rapid creation of test environments and the remote use of test tools and test services. We conduct experiments on this system and evaluate its applicability in terms of the VM provision time, VM performance and virtual network performance. The experimental results demonstrate that the performance of the VMs and virtual networks is satisfactory and that this system can improve the test efficiency and reduce test costs through rapid virtual resource provision and convenient test services.

• Journal of Multimedia Information System
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• 제7권2호
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• pp.147-156
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• 2020

The author Nakajima was involved in the field of disaster communications and emergency medical care as guest research scientist at the Fukushima Nuclear Accident Independent Investigation Commission established by the National Diet of Japan and reviewer of the Commission's report, and Kurokawa was the chairman of this Commission. Looking back over a decade, we are on the liability issue of bureaucrats and telecom operators, so it's becoming clear what was hidden at the time. The battery of NTT DoCoMo's mobile phone repeaters had a capacity of only about 24 hours, and communication failures increased after one day. The Government also failed to issue an announcement of "Vent from reactor" under the Telecommunications Act Article No. 129. This mistake lost the opportunity to use the third-party telecommunications (e.g. taxi radios). Furthermore, as a result of LASCOM (telecommunications satellite network for local governments via GEO) and a variety of unexpected communication failures, the evacuation order "Escape!" could not be notified to the general public well. As a result, the general public was exposed to unnecessary radiation exposure. Such bureaucratic slow action in emergencies is common in the response to the 2020 coronavirus.