• 한국통신학회논문지
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• 제35권11C호
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• pp.889-895
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• 2010

통신시스템에서 다수의 안테나를 이용하는 MIMO 기술이 활발히 연구 중에 있다. 그러나 많은 무선 통신기기들은 사이즈, 비용, 하드웨어의 복잡성으로 인하여 적용 가능한 안테나의 수에 제약을 가진다. 따라서 본 논문에서는 MIMO 기술의 장점을 가지면서 새로운 기술로 각광받고 있는 협력통신 시스템을 이용하여 cross-layer 부호기법을 이용한 H-ARQ 기반의 협력통신 시스템을 제안하였다. 본 논문에서 제안하는 협력통신 시스템은 수신 신호의 복호가 완벽할 시에는 ACK 신호를 소스 노드와 릴레이 노드로 전송하여 다음 신호를 요청한다. 만약 복호 후 오류가 있을 시에는 NACK 신호를 전송하여 릴레이 노드에서 생성되어진 새로운 패킷을 요청하여 복호를 하게된다. 제안하는 협력통신 시스템은 일반적인 1:1 통신 시스템보다 신뢰도와 전송효율이 더 좋음을 시뮬레이션을 통하여 확인하였다.

• 인지과학
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• 제11권1호
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• pp.67-80
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• 2000

분산 협동 정보시스템은 분산. 이질적인 정보환경에서 다양한 지식원과 문제 해결 능력 등을 가지면서 이들이 서로 통합되어 사용되는 시스템을 말한다. 이러한 시스템에서는 구성 정보를 서로 활용하고 제어할 수 있는 조정기능이 필요하고 이러한 조정기능의 역할에 따라 전체 시스템의 양태가 다양하게 결정된다. 본 논문에서는 다중에이전트 패러다임을 적용하여 분산 협동 정보시스템의 한 가지 모델을 제시하고 테스트 시스템을 구현해보았다. 제안 시스템은 분산된 구성원을 에이전트화하고 이들 간의 협동을 원활하게 할 수 있도록 조정 에이전트를 사용하고 조정 에이전트를 사용하고 있다. 본 시스템에서 제안된 조정 에이전트는 지식의 세밀도(granularity) 레벨을 이용하여 에이전트 활성화 순서를 조정한다. 즉, 처음에는 단수하면서도 빠른 속도의 지식 형태를 활용하고 그 결과에 따라 좀 더 복잡한 지식 베이스를 활용하도록 하는 것이다. 제안구조는 동일한 주제에 대하여 여러 레벨의 지식원이 존재할 때 이들을 적절히 순서화함으로써 마치 인지과정에서 의식의 초점(focusing)이 자연스럽게 바뀌는 것과 같은 효과를 얻을 수 있을 것이다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권9호
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• pp.2081-2100
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• 2013

In this paper, we propose a cooperative hybrid spectrum sharing protocol by jointly considering interweave (opportunistic) and underlay schemes. In the proposed protocol, secondary users can access the licensed spectrum along with the primary system. Our network scenario comprises a single primary transmitter-receiver (PTx-PRx) pair and a group of M secondary transmitter-receiver (STx-SRx) pairs within the transmission range of the primary system. Secondary transmitters are divided into two groups: active and inactive. A secondary transmitter that gets an opportunity to access the secondary spectrum is called "active". One of the idle or inactive secondary transmitters that achieves the primary request target rate $R_{PT}$ will be selected as a best decode-and-forward (DF) relay (Re) to forward the primary information when the data rate of the direct link between PTx and PRx falls below $R_{PT}$. We investigate the ergodic capacity and outage probability of the primary system with cooperative relaying and outage probability of the secondary system. Our theoretical and simulation results show that both the primary and secondary systems are able to achieve performance improvement in terms of outage probability. It is also shown that ergodic capacity and outage probability improve when the active secondary transmitter is located farther away from the PRx.

• Journal of Communications and Networks
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• 제15권5호
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• pp.457-463
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• 2013

In recent days, cooperative diversity and communication security become important research issues for wireless communications. In this paper, to achieve low probability of interception (LPI) and high throughput in the cooperative single-carrier frequency division multiple access (SC-FDMA) system, a new physical layer transmission scheme is proposed, where a new encryption algorithm is applied and adaptive modulation is further considered based on channel state information (CSI). By doing so, neither relay node nor eavesdropper can intercept the information signals transmitted from user terminal (UT). Simulation results show above new physical layer transmission scheme brings in high transmission safety and secrecy rate. Furthermore, by applying adaptive modulation and coding (AMC) technique according to CSI, transmission throughput can be increased significantly. Additionally, low peak-to-average power ratio (PAPR) characteristic can still be remained due to the uniform distribution of random coefficients used for encryption algorithm.

• Journal of information and communication convergence engineering
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• 제17권2호
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• pp.105-116
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• 2019

Recently, there has been an increase in research on wireless sensor networks (WSNs) because they are easy to deploy in applications such as internet-of-things (IoT) and body area networks. However, WSNs have constraints in terms of power, quality-of-service (QoS), computation, and others. To overcome the power constraint issues, wireless energy harvesting has been introduced into WSNs, the application of which has been the focus of many studies. Additionally, to improve system performance in terms of achievable rate, cooperative networks are also being explored in WSNs. We present a review on current research in the area of energy harvesting in WSNs, specifically on the application of simultaneous wireless information and power transfer (SWIPT) in a cooperative sensor network. In addition, we discuss possible future extensions of SWIPT and cooperative networks in WSNs.

• 한국정보통신학회논문지
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• 제17권8호
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• pp.1811-1819
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• 2013

본 논문에서는 무선통신에서의 시스템 성능을 향상시키기 위해 협력통신에서 매우 중요한 도움노드를 선정하는 방법에 대하여 연구를 수행하였다. 본 논문에서 제안한 BT-COMAC (busy tone cooperative MAC) 프로토콜은 사후(reactive) 도움노드 선정기법을 채용하였으며, 기존 기법의 장점을 극대화하면서 단점을 보완한 새로운 협력통신용 MAC 프로토콜이다. 컴퓨터 모의실험을 통해 성능평가를 수행하였으며, 시스템 처리량과 채널 액세스 지연시간을 성능평가 척도로 사용하였다. 모든 통신노드들이 통신영역 내에서 독자적으로 움직이는 이동성 모델을 사용하였으며, 슬로우 페이딩 채널 환경에서 수신 전력을 기반으로 전송속도를 결정하는 방법을 사용하였다. 성능평가 결과 본 논문에서 제안한 기법이 기존 방식에 비해 시스템 처리량 측면에서 최대 15% 정도 성능개선을 달성한 것을 확인할 수 있었다.

• 한국지능정보시스템학회:학술대회논문집
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• 한국지능정보시스템학회 2007년도 한국지능정보시스템학회
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• pp.189-196
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• 2007

본 논문에서는 다인수 학급에서 한계를 나타내고 있는 교육현장에서의 협력작업을 학급 및 학생 개인별 블로그 운영을 통해 해결하는 방안을 제시한다. 이를 위해 우선 학급 홈페이지 등 기존 협력작업 웹사이트의 문제점을 분석하고, 도출된 문제점을 해결하기 위 한 블로 그의 기능과 특징 등 을 도입하여 보다 효율 적인 협력 작업 시스템을 설 계 및 구현하고자 한 다.

• 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.

• 디지털산업정보학회논문지
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• 제11권1호
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• pp.135-144
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• 2015

This study aims to propose an evaluation model that enables cooperative learning using e-Learning system. Even if the teacher and the student are not in the same place at the same time, the team project deliverable submitted by the student to the online system can be viewed by the teacher, enabling the teacher to assess the student not only based on the project but also in many other aspects. The proposed e-learning cooperative learning model allows the development of assessment factors, using such factors in assessment of the student's activities which are performed through the e-learning system, and the feedback of the results to the student so that the student is further motivated for learning. The teacher performs a comprehensive assessment of such factors, which is considered in conjunction with the student's assessment. Implementing the cooperative learning model proposed in this study in various e-learning systems such as Moodle is expected to motivate the student for learning, produces better cooperative learning results, provides greater convenience of assessment to the teacher, and improves fairness of assessment by showing the student's activities in real time.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권12호
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• pp.5149-5173
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• 2016

Cooperative forwarding has shown a substantial network performance improvement compared to traditional routing in multi-hop wireless network. To further enhance the system throughput, especially in the presence of highly congested multiple cross traffic flows, a promising way is to incorporate the multi-radio multi-channel (MRMC) capability into cooperative forwarding. However, it requires to jointly address multiple issues. These include radio-channel assignment, routing metric computation, candidate relay set selection, candidate relay prioritization, data broadcasting over multi-radio multi-channel, and best relay selection using a coordination scheme. In this paper, we propose a simple and efficient cluster-based cooperative data forwarding (CCDF) which jointly addresses all these issues. We study the performance impact when the same candidate relay set is being used for multiple cross traffic flows in the network. The network simulation shows that the CCDF with MRMC not only retains the advantage of receiver diversity in cooperative forwarding but also minimizes the interference, which therefore further enhances the system throughput for the network with multiple cross traffic flows.