• 한국통신학회논문지
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• 제33권10B호
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• pp.911-918
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• 2008

본 논문에서는 방향성 안테나를 이용하여 3섹터 구조를 갖는 Narrow-Beam Trisector Cell (NBTC)과 Wide-Beam Trisector Cell (WBTC) 구조의 WiBro 시스템에 IEEE802.16j 기반의 멀티홉 중계기를 도입하여 커버리지를 확장하는 새로운 형태의 NBTC와 WBTC 구조를 제안한다. 제안한 구조는 최적화 모델을 통해 트래픽 분포에 따른 최적 배치된 기지국과 멀티홉 중계기의 수, 각 기지국의 확장되는 커버리지, 그리고 설치비용 등을 기지국만 배치하는 기존의 전형적인 구조와 비교 분석하였다. 분석 결과를 통해 주어진 전체면적에 중계기를 효율적으로 배치한다면 절약되는 설치비용을 알 수 있었고, 제안하는 멀티홉 중계기가 도입된 NBTC와 WBTC 방식 중에서 트래픽 분포가 높은 지역에서는 WBTC 방법을 이용하고, 트래픽 분포가 적은 지역에서는 NBTC 방법을 이용한다면 커버리지 확장과 설치비용 절약 측면에서 보다 효율적임을 알 수 있었다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.11-12
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• 2013

In this research, a novel multi-converter system for the fuel cell diagnostics and the load leveling function under varying load condition is proposed. The proposed system is composed of two converters and operates in two different modes. In the normal mode operation the additional bidirectional converter is used for the load leveling and in the diagnostic mode it is used for implementing integral diagnostics by way of electrochemical impedance spectroscopy (EIS). The proposed method can perform the EIS for fuel cell under varying load conditions with no influence to the load. The validity and feasibility of the proposed system is verified by the experiments and the design procedure of the proposed system is detailed.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.151-152
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• 2006

Multi-hop system has advantage of low power consumption, improved cell capacity, and enlarged service coverage. Most of previous researches show that multi-hop relaying beyond dual-hop relaying does not improve system performance significantly. This leads most researches are focused on dual-hop relaying system. In this paper, we propose an optimal boundary condition to support maximal data rate for fluctuation of traffic load in single cell dual-hop relay system.

• 인터넷정보학회논문지
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• 제22권6호
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• pp.9-15
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• 2021

고밀도 이기종 네트워크에서 스몰셀 기지국(Small-cell base station, SBS)의 수가 증가하면 매크로 단말(Macrocell user equipment, MUE)의 간섭량도 증가하여 수신 신호대 간섭 및 잡음비(Signal-to-interference and noise ratio, SINR)와 시스템 용량이 감소한다. 따라서, 본 논문에서는 SBS의 수가 증가하여도 MUE의 성능을 보장하기 위한 스몰셀 기반 다중점 협력통신(Cooperative Multi-Point, CoMP) 방법을 제안한다. 제안하는 방법은 MUE가 주어진 SINR 임계값을 만족하기 위해 주변에 위치한 SBS들을 선택하고, 선택된 SBS는 MUE에게 CoMP를 제공하여 성능을 향상시킨다. 시뮬레이션 결과를 통해 제안하는 스몰셀 기반 CoMP 방법이 다른 간섭관리 및 CoMP 방법과 비교해 스몰셀 단말의 성능은 크게 감소되지 않으면서 MUE의 평균 SINR과 시스템 용량이 향상됨을 보인다.

• 한국통신학회논문지
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• 제41권3호
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• pp.285-297
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• 2016

본 논문에서는 기지국에 다수개의 빔포밍 안테나들을 장착한 형태의 중앙 집중형 밀리미터파 기반 다중 스팟빔 셀룰러 시스템 구조와 이 시스템 운용의 핵심 개념인 다계층 동적 셀 구성 방법 그리고 이를 이용한 이동성 관리 방법을 소개하고 있다. 차단이 없는 이상적 환경에서의 시스템 시뮬레이션 결과를 통하여 밀리미터파를 이용한 이러한 시스템 구조 및 운용이 기존 셀룰러 시스템 대비 시스템 용량을 크게 높여줄 수 있고 유사한 이동 성능을 제공할 수 있다는 가능성을 보여 주고 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권2호
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• pp.288-307
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• 2013

This paper formulates resource allocation for decode-and-forward (DF) relay assisted multi-cell orthogonal frequency division multiple (OFDM) networks as an optimization problem taking into account of inter-cell interference and users fairness. To maximize the transmit rate of system we propose a joint interference coordination, subcarrier and power allocation algorithm. To reduce the complexity, this semi-distributed algorithm divides the primal optimization into three sub-optimization problems, which transforms the mixed binary nonlinear programming problem (BNLP) into standard convex optimization problems. The first layer optimization problem is used to get the optimal subcarrier distribution index. The second is to solve the problem that how to allocate power optimally in a certain subcarrier distribution order. Based on the concept of equivalent channel gain (ECG) we transform the max-min function into standard closed expression. Subsequently, with the aid of dual decomposition, water-filling theorem and iterative power allocation algorithm the optimal solution of the original problem can be got with acceptable complexity. The third sub-problem considers dynamic co-channel interference caused by adjacent cells and redistributes resources to achieve the goal of maximizing system throughput. Finally, simulation results are provided to corroborate the proposed algorithm.

• 한국수소및신에너지학회논문집
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• 제19권2호
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• pp.118-123
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• 2008

For the hydrogen recirculation system of the PEMFC (polymer electrolyte membrane fuel cell), the ejector is useful to improve the efficiency of the fuel cell system. However, conventional ejector does not keep its entrainment ratio good when the various power duties is required by the fuel cell system. In this study, the variable multi-ejector acceptable in the whole duty range required from the fuel cell hybrid mini-bus is developed. Consequently, the performance of the developed ejector is verified by the experiments based on the real operating conditions.

• 조명전기설비학회논문지
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• 제25권11호
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• pp.83-90
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• 2011

There are two main types of concentrating optical systems in use today: refractive types that use Fresnel lenses, and reflective systems that use one or more mirrors. Regardless of the chosen optical system, the result is concentrated sunlight being aimed at the sensitive face of the cell, to produce more energy from less photovoltaic material. In this paper, for the achieve trackerless CPV system, CPV module included that the spherical lens with reflect mirror makes it possible to achieve high and stable power generation performance for the high concentration photovoltaic power generation system and cope with the needs for a variety of shapes and sizes in flexible manners and that the multiple cavity assemble method greatly reduces costs. Development of these high performance multi-junction CPV module promises to accelerate growth in photovoltaic power generation.

• 한국세라믹학회지
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• 제42권12호
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• pp.865-871
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• 2005

Submicron thick solid electrolyte membrane is essential to the implementation of low temperature solid oxide fuel cell, and, therefore, development of new electrode structures is necessary for the submicron thick solid electrolyte deposition while providing functions as current collector and fuel transport channel. In this research, a nickel membrane with multi-stage nano hole array has been produced via modified two step replication process. The obtained membrane has practical size of 12mm diameter and $50{\mu}m$ thickness. The multi-stage nature provides 20nm pores on one side and 200nm on the other side. The 20nm side provides catalyst layer and $30\~40\%$ planar porosity was measured. The successful deposition of submicron thick yttria stabilized zirconia membrane on the substrate shows the possibility of achieving a low temperature solid oxide fuel cell.

• 한국경영과학회지
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• 제26권1호
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• pp.71-85
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• 2001

This paper considers a cost model for a U-shaped manufacturing cell formation which incorporates a required number of machines and various material flows together under multi-part multi-cell environment. The model is required to satisfy both the specified operation sequence of each part and the total part demand volume, which are considered to derive material handling cost in U-shaped flow line cells. In the model several cost-incurring factors including set-up for batch change-over, processing time for operations of each part, and machine failures are also considered in association with processing load and capacity of each cell. Moreover, a heuristic for a good machine layout in each cell is newly proposed based on the material handling cost of each alternative sequence layout. These all are put together to present an efficient heuristic for the U-shaped independent-cell formation problem, numerical problems are solved to illustrate the algorithm.