• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.11
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• pp.4224-4243
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• 2021

Cognitive radio (CR) is a feasible intelligent technology and can be used as an effective solution to spectrum scarcity and underutilization. As the key function of CR, cooperative spectrum sensing (CSS) is able to effectively prevent the harmful interference with primary users (PUs) and identify the available spectrum resources by exploiting the spatial diversity of multiple secondary users (SUs). However, the open nature of the cognitive radio networks (CRNs) framework makes CSS face many security threats, such as, the malicious user (MU) launches Byzantine attack to undermine CRNs. For this aim, we make an in-depth analysis of the motive and purpose from the MU's perspective in the interweave CR system, aiming to provide the future guideline for defense strategies. First, we formulate a dynamic Byzantine attack model by analyzing Byzantine behaviors in the process of CSS. On the basis of this, we further make an investigation on the condition of making the fusion center (FC) blind when the fusion rule is unknown for the MU. Moreover, the throughput and interference to the primary network are taken into consideration to evaluate the impact of Byzantine attack on the interweave CR system, and then analyze the optimal strategy of Byzantine attack when the fusion rule is known. Finally, theoretical proofs and simulation results verify the correctness and effectiveness of analyses about the impact of Byzantine attack strategy on the throughput and interference.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.7
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• pp.22-31
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• 2008

Cognitive radio should imply a proper sensing technique for detecting the presence of licensed users to identify the unused spectrum holes. Besides this, this information should also be used to opportunistically provide communication among secondary users. At the same time the performance of the primary user should not be declined by the secondary users. The detection of licensed users may be significantly difficult for shadowing effect. To prevail over this problem cooperative spectrum sensing, In which the combined observation information gained by multiple secondary users is employed to achieve higher performance of detection, has been inspected. However, the primary challenge of cooperative sensing lays in its ability to detect the presence of licensed user quickly and accurately. In this paper, we have used UltraWideBand (UWB) to detect the presence of licensed users and transmit the sensing information among the nodes of the network. UWB has the capability of transmitting data at a very high rate. It is unique in co-existence capability with narrow band systems. Here, we have shown that the detection probability of licensed user is improved by means of transmitting the spectrum sensing information via UWB. We also have analyzed the throughput of the proposed technique and compared the result with existing sensing method.

• Journal of Korean Society of Rural Planning
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• v.13 no.2
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• pp.93-105
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• 2007

Allotment gardens with log house in rural area as a rural growth tool are able to adapt to current market mechanisms by communication and promotion techniques. It is important to know what and how allotment garden's users seek their benefits to market segmentations. The primary purpose of this study was to segment and profile the benefits of allotment garden's potential users so as to provide a better understanding of allotment garden in Korea. A self-administered survey was obtained from 298 allotment gardens users in the study area. Four distinct segments were identified based on the benefits; relaxer(23.7%), educator(21.9%), want-it-all gardener(42.3%), and grower(12.2%), and these were profiled with respect to socio-demographics and civic garden-related features. We suggest that the relaxers are target market of allotment gardens with log house because they have willingly intented to pay a higher rent.

• Journal of Korean Library and Information Science Society
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• v.30 no.1
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• pp.171-192
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• 1999

Unlike the past, university libraries are able to provide specialized and differentiated information services due to the advent of information technology and telecommunication. Such services are essential not only to the primary users, such as professors and students in the universities, but also to the external users including corporations, researchers, and the general public. Now, university libraries as a means of resource sharing with communities should develop the services to play a role as a research and information center and expand such services to outside users who need the information services. Accordingly financial support is a necessity to provide the services, thereby fee-based information services are one of the devices for solving the financial burden and controlling outside users. This paper tries to present a program for fee-based information services which are able to be implemented by university libraries. Also the papers deals with the present conditions of fee-based information services provided by university libraries briefly and the goals of the program; coverage of subjects and types of materials for the program; organizations and staff; types of fee-based information services; management methods of program.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1336-1356
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• 2017

The spectrum scarcity crisis has resulted in a shortage of resources for many emerging wireless services, and research on dynamic spectrum management has been used to solve this problem. Game theory can allocate resources to users in an economic way through market competition. In this paper, we propose a bidding game-based spectrum allocation mechanism in cognitive radio network. In our framework, primary networks provide heterogeneous wireless service and different numbers of channels, while secondary users have diverse bandwidth demands for transmission. Considering the features of traffic and QoS demands, we design a weighted interference graph-based grouping algorithm to divide users into several groups and construct the non-interference user-set in the first step. In the second step, we propose the dynamic bidding game-based spectrum allocation strategy; we analyze both buyer's and seller's revenue and determine the best allocation strategy. We also prove that our mechanism can achieve balanced pricing schema in competition. Theoretical and simulation results show that our strategy provides a feasible solution to improve spectrum utilization, can maximize overall utility and guarantee users' individual rationality.

• Journal of the Korean housing association
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• v.17 no.1
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• pp.97-105
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• 2006

The purposes of this study are to find out the current status and features of earth housing, and to explore users' level of satisfaction and needs of improvement about earth housing. Primary findings are as follows: (1) The area of earth housing is generally 25-34 pyong and the construction cost of earth housing is usually 3,000,000-3,400,000 won per pyong. (2) The age of earth house users is generally forties, fifties, and sixties. And their occupation is usually retiree and farmer. The age of earth based pension users is generally twenties and thirties. (3) The construction method of earth housing is usually earth brick structure reinforced with wood structure and earth brick structure(adobe). (4) The finish of outer wall is generally earth brick laying and earth plaster. And the finish of inner wall is usually wall paper and earth plaster. Roof tile and asphalt shingle is frequently observed as roof finish. (5) Users' satisfaction about earth housing is investigated high level. Especially, the satisfaction degrees about faculty of humidity control, stink elimination, prevention from sick house syndrome, support for psychological stabilization and deep sleep are observed very highly. (6) Reduction of construction cost and prevention of crack is investigated as needs of improvement about earth housing.

• The Journal of Korean Association of Computer Education
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• v.14 no.1
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• pp.123-135
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• 2011

In this paper, we propose a system that starts with the searching result of user's query and continuously offers new keywords related to the query. The primary purpose of the proposed system is to help users find information that the users cannot explain clearly. The proposed system obtains useful information by connecting different information sources, represents the information under an integrated schema, and offers a cross searching environment. In addition, it presents a visualized diagram that shows relations between keywords so that users can easily find the desired information. Therefore users can find information easily in an envirionment that is not limited to a certain site.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.7
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• pp.2231-2245
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• 2014

Cognitive Radio (CR) has very promising potential to improve spectrum utilization by allowing unlicensed Secondary Users (SUs) to access the spectrum dynamically without disturbing licensed Primary Users (PUs). Mitigating interference is a fundamental problem in CR scenarios. This is particularly problematic for deploying CR in cellular networks, when users are located at the cell edge, as the inter-cell interference mitigation and frequency reuse are critical requirements for both PUs and SUs. Further cellular networks require higher cell edge performance, then SUs will meet more challenges than PUs. To solve the performance decrease for SUs at the cell edge, a novel Dynamic Spectrum Allocation (DSA) scheme based on Game Theory is proposed in this paper. Full frequency reuse can be realized as well as inter-cell interference mitigated according to SUs' sensing, measurement and interaction in this scheme. A joint power/channel allocation algorithm is proposed to improve both cell-edge user experience and network performance through distributed pricing calculation and exchange based on game theory. Analytical proof is presented and simulation results show that the proposed scheme achieves high efficiency of spectrum usage and improvement of cell edge SUs' performance.

• Journal of Communications and Networks
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• v.17 no.4
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• pp.440-448
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• 2015

In this paper, we study the problem of selfish behavior of secondary users (SUs) based on cognitive radio (CR) with the presence of primary users (PUs). SUs are assumed to contend on a channel using the carrier sense multiple access with collision avoidance (CSMA/CA) and PUs do not consider transmission of SUs, where CSMA/CA protocols rely on the random deference of packets. SUs are vulnerable to selfish attacks by which selfish users could pick short random deference to obtain a larger share of the available bandwidth at the expense of other SUs. In this paper, game theory is used to study the systematic cheating of SUs in the presence of PUs in multichannel CR networks. We study two cases: A single cheater and multiple cheaters acting without any restraint. We identify the Pareto-optimal point of operation of a network with multiple cheaters and also derive the Nash equilibrium of the network. We use cooperative game theory to drive the Pareto optimality of selfish SUs without interfering with the activity of PUs. We show the influence of the activity of PUs in the equilibrium of the whole network.

• The Mathematical Education
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• v.45 no.2 s.113
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• pp.205-215
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• 2006

One of the most important concepts in the 7th curriculum of Korea is the student-centered education. Since educational evaluation has significant influence on the whole curriculum, if we realize the importance of the student-center education on the curriculum we should establish the student-centered educational evaluation system. Educational evaluation is defined by the theory of information to permit information users to identify, to measure, to manipulate and to communicate useful educational information concerning an educational curriculum for making decisions. If we accept the above definitions, the demands of information users are significant in the light of conceptual framework of educational evaluation. The purpose of this study is to analyze the conceptual framework of educational evaluation from information users' perspectives and to investigate the qualitative characteristics which satisfy information users' need for making decisions. We also show that students aren't provided sufficient evaluation results information to decide for their study plans by analyzing an evaluation study of the 7th primary curriculum. Finally, this study suggests how to improve an evaluation system for students in mathematics.