• 한국항행학회논문지
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• 제14권3호
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• pp.367-374
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• 2010

본 연구는 900MHz대역을 사용하는 TA(Talk-Around)와 RFID 시스템간의 주파수 공유 가능성에 대하여 연구하였다. TA의 FHSS(Frequency Hopping Spread Spectrum)방식에서의 변조방식은 FSK(Frequency Shift Keying)디지털 변조방식을 사용하고 있고 RFID는 ASK(Amplitude Shift Keying) 디지털 변조방식을 적용하고 있다. 주파수 공유 가능성에 대한 현장시험 대상 RFID시스템은 FHSS방식이었다. 현장시험은 다섯 가지의 시나리오에 의하여 진행되었다. 현장 시험용 RFID시스템은 미국제품으로 4개의 태그와 2개의 주 장치로 구성되었다. 테스트를 위하여 TA 4대와 에질런트 스펙트럼 아날라이져가 사용되었다. 변조방식의 차별화에 의한 주파수 공유 가능성을 이론적으로 분석하였다. 시뮬레이션 결과, 이론적으로 두 변조방식 간에 주파수 공유가 가능한 것으로 분석되었다. 현장시험결과에 의하여도 TA의 신호가 RFID 신호에 영향을 주지 않는 것으로 나타났다.

• 전기전자학회논문지
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• 제26권4호
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• pp.693-704
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• 2022

5G 서비스는 기존 이동통신주파수보다 상대적으로 높은 중대역(n78)을 사용하고 있어서 2GHz 이하의 저대역 주파수를 활용하여 5G 커버리지 개선이 필요하다. 이를 위해서는 저대역 주파수의 대부분을 사용하는 LTE와 5G-NR 시스템의 동적 스펙트럼 공유(Dynamic Spectrum Sharing) 기술의 적용이 요구된다. 본 논문에서는 DSS 적용을 위한 시그널링 오버헤드 요소와 단말기 구현 RF 이슈들을 도출하고, 저대역 주파수 중 광대역 주파수 활용이 가능한 1.8GHz 대역(50MHz 폭)에 대해 5G-NR과 LTE 각각의 관점에서 시그널링 오버헤드 비율과 단말기 RF 이슈들을 분석하였다. 분석 결과들을 통해 저대역을 활용한 DSS 기술을 적용한다면 LTE 트래픽이 5G-NR로 빠르게 이전할 경우, 5G 커버리지 개선으로 인해 우수한 서비스 품질을 제공할 수 있을 것으로 예상된다.

• Journal of Power Electronics
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• 제19권6호
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• pp.1575-1581
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• 2019

Due to the mismatched line impedance among distributed generation units (DGs) and uncontrolled harmonic current, the droop controller has a number of problems such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To solve these problems, this paper proposes a resistive-capacitive virtual impedance control method. The proposed control method modifies the DG output impedance at the fundamental and harmonic frequencies to compensate the mismatched line impedance among DGs and to regulate the harmonic current. Finally, reactive power sharing is accurately achieved, and the PCC voltage distortion is compensated. In addition, adaptively controlling the virtual impedance guarantees compensation performance in spite of load changes. The effectiveness of the proposed control method was verified by experimental results.

• 대한지역사회영양학회지
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• 제8권3호
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• pp.280-287
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• 2003

To investigate effects of the shared living on nutrient intakes,250 college male students who were living alone (104 men) or sharing accommodation with friends (134 men) were participated. Their average age was 22.6 years, their average height was 171.8 cm, their average weight was 65.6 kg and their average Body Mass Index (BMI) was 22.2. The caloric intakes of the men living alone or sharing accommodation were 55.9% and 72.5% of the Korean Recommended Dietary Allowance (RDA), respectively. The decreased caloric level of the group living alone seemed to be due to their decreased protein and fat consumption as compared to that of the group sharing accommodation. The group living alone consumed increased amounts of fiber for breakfast and half the carbohydrates, but more fat (p < 0.05) in snacks than the group sharing accommodation. The daily carbohydrate : protein : fat (C : P : F) ratio averaged 58.6 14.1 27.3, which is a lower carbohydrate and a higher fat ratio than the Korean recommended ratio. However, the group living alone was closer to the Korean recommended ratio than the group sharing accommodation. The food intake habits were evaluated as being poorer in the group living alone as compared to the group sharing accommodation, less frequent consumption of fried / pan-fried dishes, and fruits / juices, but more frequent consumption of instant / processed foods. In comparing the eating patterns of the two groups, the group living alone showed better eating habits, such as more“breakfast eating”and less“snacking in the morning, afternoon or late at night”whereas the group sharing accommodation showed better eating habits such as less“picky eaters”and less “eating out”. In the group living alone, their lower caloric intake was assumably due to their fewer side dishes, however they showed higher eating frequencies of instant i processed foods. Since the lifestyle of living alone seems to grow gradually among young men, we strongly recommend dietary education for them.

• ETRI Journal
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• 제44권4호
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• pp.531-542
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• 2022

With the increasing demand for unlicensed spectrum, several regulators have been opening up the 6-GHz band for unlicensed use while ensuring compliance with the technical requirement to avoid harmful interference in the existing primary services (PSs). In this paper, we present two methodologies, a channel-based method and a frequency-based method, which are applicable to a frequency coordination system that calculates the permissible transmit power in the channels or frequencies available to a secondary service (SS). In addition, we have demonstrated that the available transmit power of an SS can be maximized by adjusting the power allocation of the assigned resource units under the condition that the channel of the SS is partially overlapped with that of the PS. Based on the analysis results, it is suggested that it would be better to utilize the two methods selectively according to the operating channel conditions of the PS and the SS.

• 전기전자학회논문지
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• 제28권3호
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• pp.440-444
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• 2024

본 논문은 유전 알고리즘을 활용하여 저궤도 위성 네트워크(LEO)와 다른 서비스 간의 주파수 공존 문제에 대한 해결 방안을 제시한다. LEO 위성을 이용하는 비지상 네트워크(NTN)는 동적 특성을 가지고 있으며, 전파 규칙에 따라 타 서비스와 주파수를 공유할 때 발생할 수 있는 간섭 문제를 해결해야 한다. 본 연구에서는 3GPP에서 제안한 NTN 운용 시나리오를 기반으로 간섭 시나리오를 모델링하고, 유전 알고리즘을 통해 NTN이 지상 서비스를 보호하면서도 최소한의 서비스 품질(QoS)를 만족하는 최적의 채널 할당방안을 도출하였다. 시뮬레이션 결과, 제안된 방법은 기존의 고정 할당 방식이나 그래프 컬러링 방식보다 우수한 성능을 보였으며, 효율적인 주파수 공유가 가능함을 확인하였다.

• 한국전자파학회논문지
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• 제27권7호
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• pp.599-611
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• 2016

본 논문은 주파수 공동사용 체계를 기반으로 군 전술 통신망 환경에서 동적 스펙트럼 접속 실현이 가능한 인지엔진 플랫폼을 제안하였다. 현재의 군 전술 무선통신 체계는 동종 및 이종의 군 전술 무선통신의 효과적 운용을 위한 추가 주파수 확보 및 무기체계 무선망 간의 상호공존 방안에 대한 필요성이 빠르게 증가하고 있는 실정이다. 본 논문은 추가 주파수 확보 방안으로 미국 및 유럽을 중심으로 활발한 연구개발이 진행되고 있는 주파수 공동사용에 대한 정책 및 연구개발 추진현황에 대해 살펴보았다. 또한, 동적 스펙트럼 접속(DSA: Dynamic Spectrum Access)을 위한 군 전술 무선통신분야의 핵심 기술인 인지엔진 기술개발 현황에 대해서도 소개하였다. 이를 통하여 본 논문은 최신 트랜드 흐름을 고려하여 향후 군 전술 무선통신에서 추가 주파수 확보 및 동적 스펙트럼 접속의 실현, 무기체계 무선망 간 상호공존이 가능한 주파수 공동사용 기반의 인지엔진 플랫폼 구조에 대해 제안하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권8호
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• pp.1894-1912
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• 2012

This paper proposes a system called Wireless Link based on Global Communication Channel (WLGCC) to enhance the spectrum sharing between digital broadcasting (DB) services and the cognitive radio (CR) system in the licensed band of 470-790 MHz. The WLGCC aims to enhance the spectrum sensing and geolocation database (GLD) spectrum sharing methods in the CR system. Spectrum sensing can be enhanced by receiving the status of the used frequencies from the WLGCC, thereby eliminating the need for a low detection threshold (i.e., avoiding the hidden node problem). In addition, the GLD can be enhanced by providing a reliable communication link between the database and the CR device in the form of an unused TV white space that is reserved as the proposed Global Communication Channel (GCC). This paper analyzes the coexistence of the new WLGCC system and the DB service in terms of avoiding additional interference. Specifically, we mathematically determine the WLGCC parameters, such as the in-band and out-of-band power levels, and operation coverage, and verify them using Monte Carlo simulation. The results show that WLGCC does not degrade the existing DB service and reliably transmits information of the vacant (or used) frequency bands to the CR.

• Journal of Power Electronics
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• 제17권1호
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• pp.200-211
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• 2017

Conventional boost-full-bridge and boost-hybrid-bridge two-stage inverters are widely applied in order to adapt to the wide dc input voltage range of photovoltaic arrays. However, the efficiency of the conventional topology is not fully optimized because additional switching losses are generated in the voltage conversion so that the input voltage rises and then falls. Moreover, the electrolytic capacitors in a dc-link lead to a larger volume combined with increases in both weight and cost. This paper proposes a higher efficiency inverter with time-sharing synchronous modulation. The energy transmission paths, wheeling branches and switching losses for the high-frequency switches are optimized so that the overall efficiency is greatly improved. In this paper, a contrastive analysis of the component losses for the conventional and proposed inverter topologies is carried out in MATLAB. Finally, the high-efficiency under different switching frequencies and different input voltages is verified by a 3 kW prototype.

• 가정과삶의질연구
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• 제19권1호
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• pp.1-16
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• 2001

This study examined the level of experienced problem and related variables of farming women as a part of study on problem diagnosis and status enhancement of rural women. The subjects were 980 married farming women living in rural area. Data were analyzed by frequencies, percentages, mean, standard deviation, factor analysis, t-test, ANOVA, Duncan-test, and multiple regression. The major findings were as follows : 1) Rural women experienced five categorized problems(farming work & health problem, institution & facilities problem, personality differences & communication problem with husband, child & in-law relatives problem, and husbands violence & sexual problem. 2) The significant variables that influenced on experienced problems were conflict coping behaviors, husbands housework participation, farming work time, age, the level of health, and income etc. Additionally socio-demographic factors, their vocational consciousness, housework sharing, and couples difference of sex-role attitude as related variables of the level of experienced problem of farming women were exmained and discussed the implication.