• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권2호
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• pp.629-648
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• 2012

Given a video stream delivering system deployed on a multicast tree, which is embedded in a multi-channel multi-radio wireless mesh network, our problem is concerned about how to allocate interference-free channels to tree links and maximize the number of serviced mesh clients at the same time. In this paper, we propose a channel allocation heuristic algorithm based on best-first search and backtracking techniques. The experimental results show that our BFB based CA algorithm outperforms previous methods such as DFS and BFS based CA methods. This superiority is due to the backtracking technique used in BFB approach. It allows previous channel-allocated links to have feasibility to select the other eligible channels when no conflict-free channel can be found for the current link during the CA process. In addition to that, we also propose a tree refinement method to enhance the quality of channel-allocated trees by adding uncovered destinations at the cost of deletion of some covered destinations. Our aim of this refinement is to increase the number of serviced mesh clients. According to our simulation results, it is proved to be an effective method for improving multicast trees produced by BFB, BFS and DFS CA algorithms.

• 한국공간정보시스템학회 논문지
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• 제2권2호
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• pp.39-48
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• 2000

본 연구는 FM DARC(DAta Radio Channel) 부가방송을 이용하여 실시간 교통정보를 제공하기 위한 교통정보 변환알고리즘 개발을 목표로 한다. FM DARC 교통정보 제공시스템을 효과적으로 구축하기 위해서는 각종 검지기로부터 수집된 데이터가 하나의 표준화된 교통정보, 즉 정보의 양과 질 그리고 포맷이 같은 정보로 가공되어 전송되어야 한다. 본 연구에서는 GIS 노드-링크 체계에 기반을 둔 교통정보 변환알고리즘을 개발하여 클라이언트/서버 환경의 FM DARC 교통정보시스템을 구현하여 보았다. 본 논문은 FM DARC에 관하여 간략하게 서술한 후 GIS DB와 교통정보 변환알고리즘 그리고 구현된 시스템에 내한 내용으로 구성되었다.

• 한국산학기술학회논문지
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• 제9권2호
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• pp.544-549
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• 2008

교육행정정보시스템(NEIS)은 인터넷을 통하여 학교와 그 상위기관간의 행정 업무를 연계하기 위하여 정부에 의해 주도된 교육 분야의 혁신적 프로젝트이다. NEIS는 교육행정업무에 대한 재설계와 정보화 전략에 따라 행정서식을 표준화하여 교원의 업무를 경감시켜 보다 나은 품질의 교육을 제공하고 온라인을 통해 관련된 교육 문제를 해결하기 위해 도입되었다. 본 논문은 NEIS의 효과적인 활용에 영향을 미치는 요인들을 도출하여 이를 계층화하고, 다중 의사결정기법을 이용하여 핵심요인간의 상대적인 중요도 평가를 통해 NEIS의 효과적인 활용방안을 모색하고자 한다. 분석결과는 NEIS의 사용자들의 만족도 제고와 향후 NEIS의 개선 전략을 개발하는데 유용하게 사용될 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권5호
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• pp.2144-2165
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• 2016

In a vehicular ad hoc network, the communication links are unsteady due to the rapidly changing topology, high mobility and traffic density in the urban environment. Most of the existing geographical routing protocols rely on the continuous transmission of beacon messages to update the neighbors' presence, leading to network congestion. Source-based approaches have been proven to be inefficient in the inherently unstable network. To this end, we propose an opportunistic beaconless packet forwarding approach based on a modified handshake mechanism for the urban vehicular environment. The protocol acts differently between intersections and at the intersection to find the next forwarder node toward the destination. The modified handshake mechanism contains link quality, forward progress and directional greedy metrics to determine the best relay node in the network. After designing the protocol, we compared its performance with existing routing protocols. The simulation results show the superior performance of the proposed protocol in terms of packet delay and data delivery ratio in realistic wireless channel conditions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권12호
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• pp.5191-5211
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• 2016

It is essential to satisfy class-specific QoS constraints to provide broadband services for new generation networks. The present study proposes a QoS-driven multicast scheme for wireless networks in which the transmission rate and end-to-end delay are assumed to be bounded during a multiple multicast session. A distributed algorithm was used to identify a cost-efficient sub-graph between the source and destination which can satisfy QoS constraints of a multicast session. The model was then modified as to be applied for wireless networks in which satisfying interference constraints is the main challenge. A discrete power control scheme was also applied for the QoS-aware multicast model to accommodate the effect of transmission power level based on link capacity requirements. We also proposed random power allocation (RPA) and gradient power allocation (GPA) algorithms to efficient resource distribution each of which has different time complexity and optimality levels. Experimental results confirm that the proposed power allocation techniques decrease the number of unavailable links between intermediate nodes in the sub-graph and considerably increase the chance of finding an optimal solution.

• Journal of Communications and Networks
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• 제16권2호
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• pp.183-192
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• 2014

This paper proposes a payment-based power control scheme using non-cooperative game with a novel pricing function in cognitive radio networks (CRNs). The proposed algorithm considers the fairness of power control among second users (SUs) where the value of per SU' signal to noise ratio (SINR) or distance between SU and SU station is used as reference for punishment price setting. Due to the effect of uncertainty fading environment, the system is unable to get the link gain coefficient to control SUs' transmission power accurately, so the quality of service (QoS) requirements of SUs may not be guaranteed, and the existence of Nash equilibrium (NE) is not ensured. Therefore, an alternative iterative scheme with sliding model is presented for the non-cooperative power control game algorithm. Simulation results show that the pricing policy using SUs' SINR as price punishment reference can improve total throughput, ensure fairness and reduce total transmission power in CRNs.

• Journal of Electrical Engineering and information Science
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• 제2권3호
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• pp.29-40
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• 1997

Two asymptotic analyses of the queue length distribution at a statistical multiplexor supporting heterogeneous exponential on-off sources are considered. The first analysis is performed by approximating the cell generation rates as a multi-dimensional Ornstein-Uhlenbeck process and then applying the Benes queueing formula. In the second analysis, w state with a system of linear equations derived from the exact expressions of the dominant eigenvalue of the matrix governing the queue length distribution. Assuming that there are a large number of sources, we obtain asymptotic approximations to the dominant eigenvalue. Based on the analyses, we define a traffic descriptor to include the mean and the variance of the cell generation rate and a burstiness measure. A simple expression for the quality of service (QoS) in cell loss rate is derived in terms of the traffic descriptor parameters and the multiplexor parameters (output link capacity and buffer size). The result is then used to quantify the factors determining the required capacity of a call taking the statistical multiplexing gain into consideration. As an application of the analyses, we can use the required capacity calculation for simple yet effective connection admission control(CAC) algorithms.

• 대한전기학회논문지:전력기술부문A
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• 제55권12호
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• pp.561-569
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• 2006

Because of the trend of deregulation, power industry is going through an unprecedented transformation in North America and Europe, and there are a host of acquisitions and mergers by the private sector to position themselves to take advantage of new business opportunities. Deregulation has accelerated the development of smaller generators and fuel cells will gradually become more attractive to mainstream electricity users as they improve in capability and decrease in cost. Fuel Cell technology is surveyed and the potential of using fuel cell as a distributed generation source is presented. This paper recommends the fuel cell power plants as alternative energy sources for distributed generation in Jeju Island, Korea. This will help in increasing fuel efficiency, at least double the current thermal plants', increasing the reliability of power supply, reducing the dependency on the HVDC link, providing quality power to the growing infrastructure, and maintaining clean air in meeting the free-trade international island.

• Safety and Health at Work
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• 제5권3호
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• pp.152-157
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• 2014

Background: As health care workers face a wide range of psychosocial stressors, they are at a high risk of developing burnout syndrome, which in turn may affect hospital outcomes such as the quality and safety of provided care. The purpose of the present study was to investigate the moderating effect of job control on the relationship between workload and burnout. Methods: A total of 352 hospital workers from five Italian public hospitals completed a self-administered questionnaire that was used to measure exhaustion, cynicism, job control, and workload. Data were collected in 2013. Results: In contrast to previous studies, the results of this study supported the moderation effect of job control on the relationship between workload and exhaustion. Furthermore, the results found support for the sequential link from exhaustion to cynicism. Conclusion: This study showed the importance for hospital managers to carry out management practices that promote job control and provide employees with job resources, in order to reduce the burnout risk.

• 전력전자학회논문지
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• 제15권3호
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• pp.199-206
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• 2010

매트릭스 컨버터는 3상의 입력 전원이 전력용 반도체 스위치의 제어를 통해 3상의 부하에 직접 연결되는 에너지 변환 장치이다. 에너지 저장을 위한 직류단이 없어 매트릭스 컨버터의 입력 전류는 부하 전류와 스위치 상태에 직접 의존한다. 그러므로 불평형 또는 왜곡된 입력 전압은 원치 않은 출력 고조파 전류의 원인이 된다. 본 논문에서는 매트릭스 컨버터의 입력 전원 외란 상황에서 출력 전류를 개선하는 신경회로망 기반 전류 보상기를 제안한다. 제안된 기법 타당성과 유효성을 시뮬레이션과 실험을 통해 증명한다.