• 한국전자파학회논문지
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• 제12권7호
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• pp.1037-1047
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• 2001

본 논문에서는 역방향 링크상의 전파 음영 채널에서 불완전 전력제어 및 불완전 섹터화를 고려하여 DS/CDMA 계층 셀룰라 시스템의 용량을 분석한다. 실제 시스템에서는 이론과는 달리 완전한 전력제어가 되지 않기 때문에 불완전 전력제어, 불완전 섹터화 및 처리이득, 매크로셀의 사용자 수와 같은 파라미터를 고려하여 시스템의 용량 변화를 유도하였다. 해석한 결과, 전력제어 및 섹터화가 불완전 할수록, 매크로셀과 마이크로셀의 전력비가 커질수록, 처리이득이 작을수록, 마이크로셀의 사용자 수가 감소할수록 DS/CDMA 계층 셀룰라 시스템의 용량은 감소하였다. 또한, 계층셀 구조가 단일 매크로셀 구조에 비해 1.54 배에서 3.89 배로 사용자 용량을 증가시킬 수 있음을 보였다.

• 한국음향학회지
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• 제14권1호
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• pp.48-55
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• 1995

서비스 영역이 중심 셀로부터 3개의 궤도가 포함하고 있는 37개의 6각형 셀의 역방향 링크(이동체-기지국)에 대한 디지털 셀룰러 CDMA의 용량을 컴퓨터 시뮬레이션에 의하여 구하였다. 채널에는 shadow페이딩이 존재하며, 시스템은 이상적으로 전력제어가 이루어지고 있다고 가정하였다. 본 논문에서는 전파손실계수와 음성통화율 그리고 인접 셀의 통화량을 고려한 CDMA 시스템의 용량 평가를 통하여 CDMA 시스템의 용량은 전과손실계수가 증가하고 음성통화율이 감소함에 따라 증가하며 $\gamma=4일$ 때 아날로그 셀룰러 FM/FDMA와 디지털 셀룰러 TDMA의 용량에 비하여 각각 15배와 5배 가량 크며 인접하고 있는 셀의 통화량에 매우 민감하다는 결과를 얻었다.

• 한국통신학회논문지
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• 제28권7A호
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• pp.503-510
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• 2003

CDMA 셀룰라 시스템은 같은 시간에 같은 주파수를 모든 사용자들이 같이 사용하므로 자기 신호 외의 다른 사용자의 신호는 간섭으로 나타나 통신 품질에 영향을 미친다. 이 간섭의 양에 따라 단위 셀당 사용자 수로 정의되는 시스템의 용량이 결정되며 간섭량의 정확한 계산이 이루어져야 시스템 성능 평가를 정확히 할 수 있다. 본 논문은 임의의 겹(tiers) 구조를 갖는 다중 셀 구성의 CDMA 셀룰라 시스템의 타셀 간섭량을 계산하기 위해 Riemann-Zeta 함수를 이용하여 임의의 전파 감쇄 지수에도 적용할 수 있는 근사식을 제안하였고, 제안된 식의 수치 결과와 시뮬레이션 결과를 비교하여 그 효용을 살펴보았다. 제안된 근사식을 이용해 계산한 타셀 간섭량과 시스템 용량은 시뮬레이션을 통해 얻은 결과를 중심으로 상한과 하한을 이루고 있으며 겹 수에 따른 값의 변화가 평균 간섭 및 용량 계산치와 일치하는 결과를 얻었다. 제안된 타셀 간섭 근사식은 복합적인 전파 환경이 공존하는 계층셀(Hierarchical Cellular) 시스템에서의 간섭 및 용량 계산과 알고리즘 검증에 유용하게 사용될 수 있을 것으로 생각된다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.695-698
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• 2002

Induction heating process is one of the most efficient heating process in terms of temperature control accuracy and heating time saving. In the past study, fabrication process of cellular 6061 alloys by powder metallurgical route and induction heating process was studied. To supplement the framing conditions that studied in past study, effect of induction heating capacity and holding time at foaming temperature were investigated. Under the achieved framing conditions, teamed 6061 alloys were fabricated for variation of foaming temperature, and porosities(%)-foaming temperature curves were obtained by try-error experimental method. Uniaxial compression tests were performed to investigate the relationship between porosities(%) and stress-strain curves of framed 6061 alloy. Also, energy absorption capacity and efficiency were calculated from stress-strain curves to investigated. Moreover, dependence of plateau stress on strain rate was investigated in case of cellular 6061 alloy with low porosities(%)

• Journal of Communications and Networks
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• 제9권3호
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• pp.247-253
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• 2007

In this paper, downlink capacity of time duplex division (TDD) based cellular wireless networks utilizing fixed hopping stations is investigated. In the network, a number of fixed subscriber stations act as hopping transmission stations between base stations and far away subscribers, forming a cellular and ad hoc mobile network model. At the radio layer, TDD code division multiple access (CDMA) is selected as the radio interface due to high efficiency of frequency usage. In order to improve the system performance in terms of downlink capacity, we propose different time slot allocation schemes with the usage of fixed hopping stations, which can be selected by either random or distanced dependent schemes. Performance results obtained by computer simulation demonstrate the effectiveness of the proposed network to improve downlink system capacity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권4호
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• pp.1841-1865
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• 2017

This paper proposes a new interference mitigation scheme for device-to-device (D2D) communications underlaying a cellular network. The object of the proposed scheme is to determine the number of data streams, a precoding matrix, and a decoding matrix of D2D networks so as to maximize the system capacity given the number of data streams of a cellular network while satisfying the constraint of the inter-system interference from D2D networks to the cellular network. Unlike existing interference mitigation schemes based on the interference alignment technique, the proposed scheme operates properly regardless of the number of data streams of a cellular network and moreover it does not require changing the precoding and decoding matrices of a cellular network. The simulation results demonstrate that the proposed scheme significantly increases the system capacity by mitigating the intra- and inter-system interference.

• Journal of Information Processing Systems
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• 제2권2호
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• pp.88-94
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• 2006

In wireless cellular networks, previous researches on admission control policies and resource allocation algorithm considered the QoS (Quality of Service) in terms of CDP (Call Dropping Probability) and CBP (Call Blocking Probability). However, since the QoS was considered only within a predetermined cell capacity, the results indicated a serious overload problem of systems not guaranteeing both CDP and CBP constraints, especially in the hotspot cell. That is why a close interrelationship between CDP, CBP and cell capacity exists. Thus, it is indispensable to consider optimal cell capacity guaranteeing multiple QoS (CDP and CBP) at the time of initial cell planning for networks deployment. In this paper, we will suggest a distributed determination scheme of optimal cell capacity guaranteeing both CDP and CBP from a long-term perspective for initial cell planning. The cell-provisioning scheme is performed by using both the two-dimensional continuous-time Markov chain and an iterative method called the Gauss-Seidel method. Finally, numerical and simulation results will demonstrate that our scheme successfully determines an optimal cell capacity guaranteeing both CDP and CBP constraints for initial cell planning.

• 한국정보통신학회논문지
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• 제7권3호
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• pp.395-402
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• 2003

CDMA 셀룰라 시스템의 용량은 간섭의 양에 따라 좌우되는 특성을 갖고 있으므로 이 간섭량을 정확히 계산해야 시스템 성능 평가를 정확히 할 수 있다. 본 논문은 CDMA 셀룰라 시스템의 역방향 타셀 간섭량을 계산하기 위한 근사식을 제시하였다. 이 근사식은 Riemann-Zeta 함수를 이용하여 임의의 전파 감쇄 지수에도 적용할 수 있는 특징이 있다. 그 효용을 살펴보기 위해 계산 결과와 시뮬레이션 결과와 비교하였다. 제안된 근사식을 이용해 계산한 시스템 용량은 시뮬레이션을 통해 얻은 용량과 근사한 결과를 얻을 수 있었다. 제안된 타셀 간섭 근사식은 복합적인 전파 환경이 고려되어야 할 계층셀 시스템에서의 간섭 및 용량 계산과 알고리즘 검증에 유용하게 사용될 수 있을 것으로 생각된다.

• Food Science and Biotechnology
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• 제18권6호
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• pp.1505-1510
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• 2009

Arginyl-fructose (AF) and arginyl-fructosyl-glucose (AFG) were chemically synthesized and purified. Their in vitro and cellular antioxidant activity was investigated using oxygen radical absorbance capacity (ORAC) and cellular antioxidant activity assay, respectively. The peroxyl radical scavenging activity of AF was much higher than that of AFG, which was in good agreement with their reduction capacity to donate electrons or hydrogen atoms. On the other hand, the hydroxyl radical scavenging activity of AF was weaker than that of AFG, which was consistent with their metal chelating activity, suggesting that AFG-$Cu^{2+}$ complex may be less redox-active than AF-$Cu^{2+}$ complex due to 1 glucose molecule attached. The cellular antioxidant activity of AF and AFG appeared to depend on both their permeability into cell membrane and the scavenging activity on peroxyl or hydroxyl radicals. These results indicate that AF and AFG, Maillard reaction products, may have a high potential as a material for the development of nutraceutical food with antioxidant activity.

• Journal of Communications and Networks
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• 제10권2호
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• pp.175-185
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• 2008

In this paper, we investigate the effect of cooperative and selection relaying schemes on multiuser diversity in downlink cellular systems with fixed relay stations (RSs). Each mobile station (MS) is either directly connected to a base station (BS) and/or connected to a relay station. We first derive closed-form solutions or upper-bound of the ergodic and outage capacities of four different downlink data relaying schemes: A direct scheme, a relay scheme, a selection scheme, and a cooperative scheme. The selection scheme selects the best access link between the BS and an MS. For all schemes, the capacity of the BS-RS link is assumed to be always larger than that of RS-MS link. Half-duplex channel use and repetition based relaying schemes are assumed for relaying operations. We also analyze the system capacity in a multiuser diversity environment in which a maximum signal-to-noise ratio (SNR) scheduler is used at a base station. The result shows that the selection scheme outperforms the other three schemes in terms of link ergodic capacity, link outage capacity, and system ergodic capacity. Furthermore, our results show that cooperative and selection diversity techniques limit the performance gain that could have been achieved by the multiuser diversity technique.