• Journal of the Korea Institute of Information Security & Cryptology
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• v.21 no.1
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• pp.3-14
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• 2011

In recent days, people used to store and share the data with other users through the web storage services. It is more convenient for using the data, but it raise problems such as access control of stored data and privacy exposure to untrusted server. Searchable encryption is used to share the data securely in multi-user setting. Especially in the multi-user setting, the revoked users should not be able to search the data and access the stored data. That is, it should be considered the security from revoked users. However in the existing schemes, the revoked users can decrypt the shared data by passive attack. Proposed scheme is the secure searchable encryption that resolves the problem and guarantees the security for revoked users.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.06a
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• pp.383-386
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• 2007

Under the circumstance of Ubiquitous Society, service should be provided according to the users' location and environment. When specific service is demanded by user, the technology, which can help to detect whether there are devices performing the requested service in the ubiquitous network, is mandatory. This technology also should guarantee that users have the appropriate service through the most suitable device which is selected by this technology. The priority is an essential factor when multi service are asked by multi users simultaneouslyin the ubiquitous network, The paper focuses on realization of Smart Classroom which provides multi users, such as the professor and the students, with active services based on the Zigbee network and the Mobile platform.

• Journal of Korean Society for Geospatial Information Science
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• v.19 no.1
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• pp.13-20
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• 2011

LBS services is a user-centric location based information service, where its importance has been discussed as an essential engine in an Ubiquitous Age. We aimed to develop an ontology reasoning system that enables users to derive recommended results suitable through selection standard reasoning according to various users' preferences. In order to achieve this goal, we designed the Geo-ontology system which enabled the construction of personal characteristics of users, knowledge on personal preference and knowledge on spatial and geographical preference. We also integrated a function of reasoning relevant information through the construction of Cost Value ontology using multi-criteria decision making by giving weight according to users' preference.

• The Journal of the Korea Contents Association
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• v.6 no.4
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• pp.55-62
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• 2006

Important issues emerging with the opening of the ubiquitous age are how to present ubiquitous environment and how services and access methods can be provided to users. The present research proposes a system that can provide users with useful information dynamically through intelligent multi agents in mobile environment. The system is composed of profile module, rule generation module, filtering module and service module. It was designed to find users' demands in an intelligent way based on information on users registered through the recommendation agent. We implemented an applied system and proved its performance through an experiment.

• Journal of information and communication convergence engineering
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• v.12 no.2
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• pp.67-74
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• 2014

In multi-hop communication systems, two-way relaying is one of the solutions to mitigate the spectral efficiency loss caused by a half-duplex transmission. In this paper, a simple two-way relaying scheme is proposed for two-hop two-user multiple input multiple output (MIMO) systems. In the proposed system, a base station and a relay station (RS), both equipped with two antennas, form a point-to-point MIMO channel, while the RS and two single-antenna mobile users form a point-to-multipoint multiuser (MU)-MIMO channel. Numerical examples show that the proposed system achieves a significant sum rate gain as compared to a one-way relaying system as the distance between a relay and the two users decreases. We also show that although we can expand the proposed scheme to more than two users, its performance gain as compared to that of one-way relaying decreases with an increase in the number of users.

• Journal of Communications and Networks
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• v.17 no.3
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• pp.267-274
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• 2015

Due to the difficulty of coordination in the cellular uplink, it is a practical challenge how to achieve the optimal throughput scaling with distributed scheduling. In this paper, we propose a distributed and opportunistic user scheduling (DOUS) that achieves the optimal throughput scaling in a single-input multiple-output interfering multiple-access channel, i.e., a multi-cell uplink network, with M antennas at each base station (BS) and N users in a cell. In a distributed fashion, each BS adopts M random receive beamforming vectors and then selects M users such that both sufficiently large desired signal power and sufficiently small generating interference are guaranteed. As a main result, it is proved that full multiuser diversity gain can be achieved in each cell when a sufficiently large number of users exist. Numerical evaluation confirms that in a practical setting of the multi-cell network, the proposed DOUS outperforms the existing distributed user scheduling algorithms in terms of sum-rate.

• Journal of the Ergonomics Society of Korea
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• v.31 no.4
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• pp.499-505
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• 2012

Objective: Research on the transformation of interaction between mobile machines and users through analysis on current gesture interface technology development trend. Background: For smooth interaction between machines and users, interface technology has evolved from "command line" to "mouse", and now "touch" and "gesture recognition" have been researched and being used. In the future, the technology is destined to evolve into "multi-modal", the fusion of the visual and auditory senses and "3D multi-modal", where three dimensional virtual world and brain waves are being used. Method: Within the development of computer interface, which follows the evolution of mobile machines, actively researching gesture interface and related technologies' trend and development will be studied comprehensively. Through investigation based on gesture based information gathering techniques, they will be separated in four categories: sensor, touch, visual, and multi-modal gesture interfaces. Each category will be researched through technology trend and existing actual examples. Through this methods, the transformation of mobile machine and human interaction will be studied. Conclusion: Gesture based interface technology realizes intelligent communication skill on interaction relation ship between existing static machines and users. Thus, this technology is important element technology that will transform the interaction between a man and a machine more dynamic. Application: The result of this study may help to develop gesture interface design currently in use.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.5
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• pp.1973-1991
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• 2018

Multimedia applications over wireless networks have been evolving to augmented reality or virtual reality services. However, a rich data size compared to conventional multimedia services causes bandwidth bottlenecks over wireless networks, which is one of the main reasons why those applications are not used widely. To overcome this limitation, bandwidth aggregation techniques, which exploit a multi-path transmission, have been considered to maximize link utilization. Currently, most of the conventional researches have been focusing on the user end problems to improve the quality of service (QoS) through optimal load distribution. In this paper, we address the joint pricing and load distribution problem for multi-homing in heterogeneous wireless access networks (ANs), considering the interests of both the users and the service providers. Specifically, we consider profit from resource allocation and cost of power consumption expenditure for operation as an utility of each service provider. Here, users decide how much to request the resource and how to split the resource over heterogeneous wireless ANs to minimize their cost while supporting the required QoS. Then, service providers compete with each other by setting the price to maximize their utilities over user reactions. We study the behaviors of users and service providers by analyzing their hierarchical decision-making process as a multileader-, multifollower Stackelberg game. We show that both the user and service provider strategies are closed form solutions. Finally, we discuss how the proposed scheme is well converged to equilibrium points.

• Journal of Electrical Engineering and Technology
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• v.10 no.6
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• pp.2406-2412
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• 2015

Multi-user multi-input multi-output (MU-MIMO) system has attracted the 4^th generation wireless network as one of core technique for performance enrichment. In this system rate control is a challenging problem and another problem is optimization. Proper scheduling can resolve these problems by deciding which set of user and at which rate the users send their data. This paper proposes a new multi-parameter based scheduling (MPS) for downlink multi-user multiple-input multiple-output (MU-MIMO) system under space-time block coding (STBC) transmissions. Goal of this MPS scheme is to offer improved link level performance in terms of a low average bit error rate (BER), high packet delivery ratio (PDR) with improved resource utilization and service fairness among the user. This scheme allows the set of users to send data based on their channel quality and their demand rates. Simulation compares the MPS performance with other scheduling scheme such as fair scheduling (FS), normalized priority scheduling (NPS) and threshold based fair scheduling (TFS). The results obtained prove that MPS has significant improvement in average BER performance with improved resource utilization and fairness as compared to the other scheduling scheme.

• Journal of the Ergonomics Society of Korea
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• v.19 no.3
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• pp.77-92
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• 2000

This study is about the satisfaction and the usage of users' manual for mobile phones with multi-functions. The users' manual is redesigned by including ergonomic factors verified through survey. This paper is to propose a redesigned users' manual which is more readable and understandable than original users' manuals. The degree of improvement is measured by the usability evaluation. There are significant differences(p<0.05) in the number of functional description original users' manuals. And the degree of users' satisfaction with the description of Crystal Display) are significant diffenences among the original users' manuals. In the as of description, the significant differences are partially found. The users' manual is re arranging the explanations of functions compactly in a table form, and reducing the cl has also $3cm^*2cm$ LCD figures to facilitate the understanding. The usability evaluation users' satisfaction and understanding for the redesigned users' manual are higher than original users' manuals.