• 한국전자파학회논문지
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• 제19권5호
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• pp.506-514
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• 2008

WiBro 시스템과 같은 최근 통신 시스템에서 대역폭 효율을 증가시키기 위해 모든 셀에서 주파수를 재사용하는 경우, 셀 경계에 위치하는 수신기는 인접 셀로부터 오는 간섭 신호로 인해 수신 성능이 열화된다. 본 논문에서는 셀룰러 시스템에서 셀 경계에서의 하향 링크 성능 향상을 위해, 다수 개의 안테나를 가진 단말기에서 활용할 수 있는 수신 방식을 제안한다. 성능 검증을 위하여 인접 셀의 간섭 신호 세기 및 단말기의 안테나 개수의 변화에 따른 유효 신호 대 간섭 잡음비의 화률 밀도 함수와 대역폭 효율을 산출한다. 제안하는 방식은 MRC(Maximum Ratio Combining) 및 SD(Spatial Multiplexing) 방식 대비 유효 신호 대 간섭 잡음비와 대역폭 효율을 큰 폭으로 향상시킴을 분석 결과로 확인할 수 있으며, 실험을 통해 그 결과를 검증한다.

• 한국유체기계학회 논문집
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• 제15권3호
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• pp.57-63
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• 2012

Effects of coolant pre-cooling and fuel pre-heating on the performance of a combined cycle using a F-class gas turbine were investigated. Coolant pre-cooling results in an increase of power output but a decrease in efficiency. Performance variation due to the fuel pre-heating depends on the location of the heat source for the pre-heating in the bottoming cycle (heat recovery steam generator). It was demonstrated that a careful selection of the heat source location would enhance efficiency with a minimal power penalty. The effect of combining the coolant pre-cooling and fuel pre-heating was also investigated. It was found that a favorable combination would yield power augmentation, while efficiency remains close to the reference value.

• Smart Structures and Systems
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• 제10권3호
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• pp.193-207
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• 2012

New insights into our previously proposed hybrid-type method for vibration control are highlighted in terms of energy analysis, such as the assessment of energy efficiency and system stability. The hybrid method improves the bang-bang active method by combining it with an energy-recycling approach. Its simple configuration and low energy-consumption property are quite suitable especially for isolated structures whose energy sources are strictly limited. The harmful influence of the external voltage is assessed, as well as its beneficial performance. We show a new chattering prevention approach that both harvests electrical energy from piezoelectric actuators and eliminates the displacement-offset of the equilibrium point of structures. The amount of energy consumption of the hybrid system is assessed qualitatively and is compared with other control systems. Experiments and numerical simulations conducted on a 10-bay truss can provide a thorough energy-efficiency evaluation of the hybrid suppression system having our energy-harvesting system.

• 경영과학
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• 제34권2호
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• pp.67-83
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• 2017

This paper proposes a R&D project performance measurement model for private firms combining balanced scorecard (BSC) and data envelopment analysis (DEA). The efficiency of R&D projects is measured in terms of each of the three perspectives of BSC by using DEA : the internal process perspective (DEA-P), the customer perspective (DEA-C), and the financial perspective (DEA-F). The performance indicators of the three perspectives of BSC are considered as outputs of the corresponding DEA models. To provide strategic implications for R&D planning, we also propose the R&D project performance matrices composed of two different types of efficiency dimensions. The proposed model is expected to be fruitfully utilized for R&D performance measurement of private firms.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권3호
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• pp.142-149
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• 2002

As is well-known, the maximum power point (MPP) of PV power generation system depends on array temperature and solar insolation, it is necessary to track MPP of solar array all the time. Among various MPP control algorithms, the constant voltage control method, the perturbation and observation (P&O) method and the incremental conductance method (IncCond) have drawn many attractions due to the usefulness of each system. In this parer, the effectiveness of above mentioned three different control algorithms are thoroughly investigated via simulations and preposed efficiency evaluation method on experiment. Both the steady-state and transient characteristics of each control algorithms along with measured efficiency are analyzed, respectively. Finally, a novel MPPT control algorithm combining the constant voltage control and IncCond method for low insolation condition is proposed to improve efficiency of the 3KW PV power generation system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.207-212
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• 2002

As is well-known, the maximum power point(MPP) of PV power generation system depends on array temperature and solar insolation, it is necessary to track MPP of solar array all the time. Among various MPP control algorithms, the constant voltage control method, the perturbation and observation(P&O) method and the incremental conductance method(IncCond) have drawn many attractions due to the usefulness of each system. In this paper, the effectiveness of above mentioned three different control algorithms are thoroughly investigated via simulations and proposed efficiency evaluation method on experiment. Both the steady-state and transient characteristics of each control algorithms along with measured efficiency are analyzed, respectively. Finally, a novel MPPT control algorithm combining the constant voltage control and IncCond method for low insolation condition is proposed to improve efficiency of the 3KW PV power generation system.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2000년도 제1회 학술대회 논문집
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• pp.125-126
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• 2000

We report the use of fluorene based copolymers containing quinoline(POF66, PIF66) and pyridine(PFPV) units as electron transporting polymers for multi-layered LEDs. Double-layer device structure combining PIF66 as electron-transporting layer with the emissive MEHPPV showed a maximum quantum efficiency of 0.03%, which is 30 fold increased compared with ITO/MEHPPV/Al single-layer device. PFPV layer increased the quantum efficiency up to 0.1% in the device structure of ITO/(P-3:PVK)/PFPV/Al. The ETL with the electron deficient moiety improved the LED performance by the characteristics of electron transporting as well as hole blocking between emissive layer and metal cathode.

• 설비공학논문집
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• 제16권12호
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• pp.1197-1203
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• 2004

This study investigates the air leakage and heat transfer characteristics of a rotary-type air-to-air heat exchanger with a fiber polyester matrix. The leakage airflow rate is measured using a tracer gas method for various ventilation rates and rotational speeds of the matrix wheel. A correlation equation for air leakage is obtained by combining the pressure leakage and the carryover leakage. The pressure leakage is observed to be a function of ventilation airflow rate only, and the carryover leakage is found to be a linear function of rotational speed. The real efficiency of the heat exchanger can be obtained from its apparent efficiencies by taking into account the air leakage ratio. As the ventilation rate increases, the heat recovery efficiency decreases. As the rotational speed of the matrix increases, the efficiency increases initially but reaches a constant value for the rotational speeds over 10 rpm.

• ETRI Journal
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• 제44권6호
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• pp.885-902
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• 2022

The mmWave cell-free massive MIMO (CFmMIMO), combining the advantages of wide bandwidth in the mmWave frequency band and the high- and uniform-spectral efficiency of CFmMIMO, has recently emerged as one of the enabling technologies for 6G. In this paper, we propose a novel framework for energy-efficient mmWave CFmMIMO systems that uses low-resolution digital-analog converters (DACs) and phase shifters (PSs) to introduce lowcomplexity hybrid precoding. Additionally, we propose a heuristic pilot allocation scheme that makes the best effort to slash some interference from copilot users. The simulation results show that the proposed hybrid precoding and pilot allocation scheme outperforms the existing schemes. Furthermore, we reveal the relationship between the energy and spectral efficiencies for the proposed mmWave CFmMIMO system by modeling the whole network power consumption and observe that the introduction of low-resolution DACs and PSs is effective in increasing the energy efficiency by compromising the spectral efficiency and the network power consumption.

• 한국통신학회논문지
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• 제34권2A호
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• pp.132-138
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• 2009

무선인지 기술은 비어있는 스펙트럼을 검출하고 이를 사용하여 통신하는 기술로서 주파수 부족 현상을 해소하기 위한 방안으로 활발히 연구가 이루어지고 있다. 무선인지 기술을 도입하기 위해 핵심적인 요소는 부사용자가 주사용자의 통신을 방해하지 않으면서 주파수 사용의 효율성을 최대화하는 것이다. 이를 위해서는 주사용자의 스펙트럼 점유 여부를 정확하게 판단하는 센싱 기술이 필요하다. 각각의 부사용자가 독립적으로 센싱을 수행하는 개별 센싱 기술은 음영지역, 잠복 터미널 문제 등이 있어서 최근 여러 부사용자가 협력하여 센싱을 수행하는 협력 스펙트럼 센싱 기술이 주목받고 있다. 본 논문은 협력 스펙트럼 센싱에 있어서 각 부사용자가 개별적으로 센싱한 결과의 경판정 값을 취합하여 이를 효과적으로 결합하는 방법을 제안한다. 제안한 방법은 과거의 협력 센싱 결과를 이용하여 각 부사용자의 개별 센싱 결과에 신뢰도를 나타내는 가중치를 부여하여 결합함으로써 협력 센싱 성능을 향상시킨다. 다양한 환경에서 제안한 방법의 검출 성능을 평가하여 기존의 가중치 없는 경판정 결합 방법과 비교한 결과를 제시한다.