• Journal of Communications and Networks
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• 제14권4호
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• pp.364-373
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• 2012

In this paper, we propose combined relay selection and cooperative beamforming schemes for physical layer security. Generally, high operational complexity is required for cooperative beamforming withmultiple relays because of the required information exchange and synchronization among the relays. On the other hand, while it is desirable to reduce the number of relays participating in cooperative beamforming because of the associated complexity problem, doing so may degrade the coding gain of cooperative beamforming. Hence, we propose combined relay selection and cooperative beamforming schemes, where only two of the available relays are selected for beamforming and data transmission. The proposed schemes introduce a selection gain which partially compensates for the decrease in coding gain due to limiting the number of participating relays to two. Both the cases where full and only partial channel state information are available for relay selection and cooperative beamforming are considered. Analytical and simulation results for the proposed schemes show improved secrecy capacities compared to existing physical layer security schemes employing cooperative relays.

• 해양환경안전학회지
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• 제25권3호
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• pp.259-268
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• 2019

Even if only two ships are encountered, a collision may occur due to the mistaken judgment of the positional relationship. In other words, if an officer does not know a target ship's intention, there is always a risk of collision. In this paper, the experiments are conducted to investigate how the intention affects the action of collision avoidance in cooperative and non-cooperative situations. In non-cooperative situation, each ship chooses a course that minimizes costs based on the current situation. That is, it always performs a selfish selection. In a cooperative situation, the information is exchanged with a target ship and a course is selected based on this information. Each ship uses the Distributed Stochastic Search Algorithm so that a next-intended course can be selected by a certain probability and determines the course. In the experimental method, four virtual ships are set up to analyze the action of collision avoidance. Then, using the actual AIS data of eight ships in the strait of Dover, I compared and analyzed the action of collision avoidance in cooperative and non-cooperative situations. As a result of the experiment, the ships showed smooth trajectories in the cooperative situation, but the ship in the non-cooperative situation made frequent big changes to avoid a collision. In the case of the experiment using four ships, there was no collision in the cooperative situation regardless of the size of the safety domain, but a collision occurred between the ships when the size of the safety domain increased in cases of non-cooperation. In the case of experiments using eight ships, it was found that there are optimal parameters for collision avoidance. Also, it was possible to grasp the variation of the sailing distance and the costs according to the combination of the parameters, and it was confirmed that the setting of the parameters can have a great influence on collision avoidance among ships.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권6호
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• pp.1042-1062
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• 2010

Cooperative spectrum sensing (CSS) is an effective technology for alleviating the unreliability of local spectrum sensing due to fading/shadowing effects. Unlike most existing solutions, this paper considers the use of CSS technology in decentralized networks where a fusion center is not available. In such a decentralized network, some attackers may sneak into the ranks of cooperative users. On the basis of recent advances in bio-inspired consensus algorithms, an attack-proof, decentralized CSS scheme is proposed in which all secondary users can maintain cooperative sensing by exchanging information locally instead of requiring centralized control or data fusion. Users no longer need any prior knowledge of the network. To counter three potential categories of spectrum sensing data falsification (SSDF) attacks, some anti-attack strategies are applied to the iterative process of information exchange. This enables most authentic users to exclude potentially malicious users from their neighborhood. As represented by simulation results, the proposed scheme can generally ensure that most authentic users reach a consensus within the given number of iterations, and it also demonstrates much better robustness against different SSDF attacks than several existing schemes.

• 한국도서관정보학회지
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• 제25권
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• pp.257-293
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• 1996

This paper reviews various aspects of authouity control system and presents prerequistes for an effective authority control in our future cooperative cataloging. It can be summarized as follows. First, numerous factors affecting authority control must be analyzed and consistent procedures and policies on the authority control have to be established. Second, to make an effective bibiographic data base there must be a standard for the information processing and a systematic organization for information sharing and communicating. Third, for this objective we have to build a MARC format, establish a network for the exchange of automatic authority records among systems, standardize the transcription of multscripts, and establish a centralized automatic authority system for a consistent maintenance of authorityrecords of the union data base. Fourth, it would be one of the best way of achieving cooperative cataloging to set up such a nation-wide authority control system as the NACO in Japan.

• Journal of Communications and Networks
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• 제17권2호
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• pp.133-144
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• 2015

In this paper, we introduce a system and a set of algorithms for disseminating popular content to a large group of wireless clients spread over a wide area. This area is partitioned into multiple cells and there is a base station in each cell which is able to broadcast to the clients within its radio coverage. Dissemination of information in the proposed system is hybrid in nature: Each base station broadcasts a fraction of information in the form of random linear combinations of data blocks. Then the clients cooperate by exchanging packets to obtain their desired messages while they are moving arbitrarily over the area. In this paper, fundamental trade-offs between the average information delivery completion time at the clients and different parameters of the system such as bandwidth usage by the base stations, average energy consumption by the clients and the popularity of the spread information are studied. Moreover different heuristic algorithms are proposed to control and maintain a balance over these trade-offs. Also, the more complicated case of multiple sessions where each client is interested in an arbitrary subset of sessions is considered and two variants of the basic dissemination algorithm are proposed. The performance of all the proposed algorithms is evaluated via extensive numerical experiments.

• 한국통신학회논문지
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• 제36권3A호
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• pp.287-295
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• 2011

Cognitive radio (CR) features opportunistic access to spectrum when licensed users (LU) are not operating. To avoid interference to LU, cognitive users (CU) need to perform spectrum sensing. Because of local shadowing, fading, or limited sensing capability, it is suggested that multiple CUs cooperate to detect LU. In cooperative spectrum sensing, CUs should exchange their sensing data with minimum bandwidth and delay. In this paper, we introduce a novel method to efficiently report sensing data to the central node in an infrastructured OFDM-based CR network. All CUs simultaneously report their sensing data over unique and orthogonal signals on locally available subcarriers. By detecting the signals, the central node can determine subcarrier availability for each CU. Implementation challenges are identified and then their solutions are suggested. The proposed method is evaluated through simulation on a realistic channel model. The results show that the proposed method is feasible and efficient.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2009년도 춘계 종합학술대회 논문집
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• pp.45-50
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• 2009

이러닝의 발전과 더불어 다양한 학습도구의 개발 그리고 이러닝 콘텐츠의 공동활용 등 이러닝을 통한 교류가 활발하게 이루어 지고 있다. 그러나 각각 LMS의 상호 연동을 고려하지 않고 개발되었기 때문에 이러닝 교류시 문제점이 나타나게 되었다. 특히 대학간 이러닝 교류는 학습자 정보교환 중심의 교류, 강의(교수자) 정보교환 중심의 교류 등 여러 가지가 있으나, 이들 모두 직접적인 연계가 이루어지지 않기 때문에 여러 가지로 문제점이 많이 나타났다. 이에 본 논문에서는 이러닝 교류의 사례를 분석하고, 문제점을 도출하여 효율적인 LMS 상호 연동에 대한 모형을 설계하여 제시하였다. 우선 먼저 학습에 가장 필요로 하는 학습요소 즉, 강좌개설정보, 강의정보, 사용자정보, 수강정보, 학습이력정보를 연동 데이터로 정의하였으며, 뷰를 이용한 데이터 연동 테이블을 통해 LMS를 연동하였다. 실험결과 학습자와 교수자의 접근성이 편리하게 나타났으며, 데이터 교환이 없기 때문에 업무 프로세스가 현저히 줄었다. 향후에는 다양한 학습요소에 대한 연동과 세션처리, 보안을 고려한 LMS 연동이 연구과제로 남아있다.

• 한국가스학회지
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• 제8권2호
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• pp.28-34
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• 2004

Enhanced methodologies for process diagnosis and abnormal situation management have been developed for the last two decades. However, there is no single method that always shows better performance over all kinds of diagnostic problems. In this paper, a framework of message-passing, cooperative, intelligent diagnostic agents is presented for improved on-line fault diagnosis through cooperative problem solving of different expertise. A group of diagnostic agents in charge of different process functional perform local diagnoses in parallel; exchange related information with other diagnostic agents; and cooperatively solve the global diagnostic problem of the whole process plant or business units just like human experts would do. For their better understanding, sharing and exchanging of process knowledge and information, we also suggest a way of remodeling processes and protocols, taking into account semantic abstracts of process information and data. The benefits of the suggested multi-agents-based approach are demonstrated by the implementations for solving the diagnostic problems of various chemical processes.

• 한국항행학회논문지
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• 제15권4호
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• pp.640-645
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• 2011

이러닝의 발전과 더불어 다양한 학습도구의 개발 및 이러닝 콘텐츠의 공동 활용 등 이러닝을 통한 교류가 활발하게 이루어지고 있다. 또한 이러닝 교류는 학습자 정보교환 중심의 교류, 교수자 정보교환 중심의 교류 등 여러 가지가 있다. 그러므로 각각 LMS의 상호 연동을 고려하지 않고 개발되었기 때문에 이러닝 교류시 문제점이 나타나게 되었다. 이 문제점을 해결하기 위하여 본 논문에서는 우선 먼저 학습에 가장 필요로 하는 학습요소들 즉, 과목정보, 강의정보, 사용자정보, 수강신청정보, 학습이력정보를 연동데이터로 정의하였으며, 가상의 테이블인 뷰를 이용하여 데이터 연동 테이블을 구성하여 이러닝간 운영관리를 위한 LMS 연동 모델 구현한다. 향후에는 다양한 학습요소에 대한 연동과 세션처리, 보안을 고려한 LMS 연동이 연구과제로 남아있다.

• 한국전자파학회논문지
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• 제23권1호
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• pp.14-20
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• 2012

셀룰러 이동 통신 시스템에서 협력적으로 신호를 전송하는 CoMP(Coordinated Multi-Point transmission and reception) 방식은 기지국 간 간섭을 매우 효과적으로 제어하여 시스템의 전송률을 증가시킨다. 그러나 협력적 전송에 참여하는 기지국의 개수가 증가할수록 기지국 간 공유가 요구되는 채널 상태 정보 및 전송 데이터의 교환으로 인한 오버헤드가 비약적으로 증가하는 문제를 발생시킨다. 본 논문에서는 제한적 궤환량을 고려하여 전송 효율이 높은 기지국들만을 협력적 전송에 참여시키는 부분적 CoMP 전송 방식을 제안한다. 이를 위해 시스템 내 코어 망은 사용자가 선호하는 기지국 정보를 반영하여 협력 기지국 조합을 구성한다. 또한, 사용자들의 채널 환경에 따라 선호하는 협력 기지국 조합이 상이할 수 있으므로 코어 망은 구성된 협력 기지국 조합을 다이나믹하게 변형하여 적용한다. 컴퓨터 시뮬레이션을 이용하여 제한적 궤환량 사용 시 기존의 비협력적 기지국 전송 방식과 협력적 기지국 전송 방식과의 평균 전송률 성능을 비교하고, 이를 통해 제안 방식의 우수성을 입증한다.