• Journal of Industrial Technology
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• v.27 no.A
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• pp.141-147
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• 2007

In this paper, we define the multi-states exponential cell resident time mobility model for describing the mobility characteristics of mobile user and analyzed the total cost of the hybrid method using multi-states cell resident time. Generally, the mobile user has three states for its movement, such as staying, walking and driving. This multi-states cell resident time based hybrid method reflects the movement characteristics of mobile user and adapts the location update period according to the states of mobility speed. As a results of the performance analysis, we can get the optimum parameters of the hybrid method for multi-states based mobile users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.4
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• pp.646-652
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• 2015

In this paper, the system-level performance is evaluated for the feedback scheme on the pre-coding matrix index (PMI) and channel quality indication (CQI), which are required for user selection in the multi-user MIMO system. Our analysis demonstrates that the number of users, the number of selected users, and codebook size are the key factors that govern the performance of the best companion grouping (BCG)-based user scheduling. Accordingly, we have confirmed that the probability of forming the co-scheduled user group is determined by these factors, which implies that the number of PMI's and codebook size can be dynamically determined so as to maximize the average system throughput as the number of users varies in the cell.

• Journal of Korea Multimedia Society
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• v.24 no.3
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• pp.355-372
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• 2021

Recently, high-performance HMDs (Head-Mounted Display) are becoming wireless due to the growth of virtual reality technology. Accordingly, environmental constraints on the hardware usage are reduced, enabling multiple users to experience virtual reality within a single space simultaneously. Existing multi-user virtual reality platforms use the user's location tracking and motion sensing technology based on vision sensors and active markers. However, there is a decrease in immersion due to the problem of overlapping markers or frequent matching errors due to the reflected light. Goal of this study is to develop a multi-user virtual reality moving platform in a single space that can resolve sensing errors and user immersion decrease. In order to achieve this goal hybrid sensing technology was developed, which is the convergence of vision sensor technology for position tracking, IMU (Inertial Measurement Unit) sensor motion capture technology and gesture recognition technology based on smart gloves. In addition, integrated safety operation system was developed which does not decrease the immersion but ensures the safety of the users and supports multimodal feedback. A 6 m×6 m×2.4 m test bed was configured to verify the effectiveness of the multi-user virtual reality moving platform for four users.

• The Journal of the Korea Contents Association
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• v.10 no.5
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• pp.52-61
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• 2010

In recent, the interests of multi-user systems have been increased. Multi-user systems allow a number of users to access the system simultaneously. Security is one of the key issues to be addressed in a multi-user environment. We propose a solution based on the NTFS file system that provides the personal data security and considers the convenience of users. The system increases the convenience of users by simplifying the complexity of the security setting on NTFS. We also propose a variety of policies that prevent from the conflicts incurring when different users set up the personal folders simultaneously and do not set up the important folders such as the window system folders as personal folders. In addition, our system supports the function of setting up the prohibition folder lists so that no one can not set the folder to their personal folders.

• Proceedings of the KSPS conference
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• 2003.10a
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• pp.133-137
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• 2003

The purpose of this study was to provide acoustic data on the voice of the laryngectomized patients for more scientific and efficient voice rehabilitation. The phonation of prolonged /a/ of 9 electronic artificial larynx(AL) users, 5 esophageal(EP) speech users, and 2 tracheo-esophageal(TEP) voice users were recorded and analyzed using Multi-Speech. Habitual f0, mean f0, sd f0, max f0, min f0, jitter, shimmer, and NHR were compared among groups of subjects using t-test. The EP and TEP groups exhibited higher f0 compared to the AL group. The AL and TEP groups showed more stable f0 than the EP group. In addition, the quality of TEP and EP voices were comparatively better in terms of jitter, shimmer, and NHR.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.5 s.98
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• pp.112-123
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• 1999

Virtual reality is becoming a powerful tool for various applications such as training, entertainment, surgery, tele-robotics etc. One potential use for virtual reality is to allow several users to interact in a single virtual environment, for example several students sitting in front of different computers connected over a network. In this paper, we present a loosely coupled architecture of haptic display in the multi-user virtual world. The method of controlling haptic devices as well as the way of configuring individual haptic display system are addressed. We will develop an experimental virtual reality system for two remote users and conclude with an experimental work for the task of a multi-player ping-pong and grasping of a common object.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.4
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• pp.830-837
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• 2009

In this thesis, Multi-code/Multi-carrier CDMA(MC/MC CDMA) system which is combination of Multi-code CDMA and Multi-carrier CDMA is analyzed. This system is suitable fur multi-rate services that use multi-codes and high data rate transmission that employ multi-carriers. In addition, the MC/MC CDMA system is robust against frequency selective fading, is good for narrowband interference rejection, and has higher spectral efficiency. In this paper, The users are assigned OVSF codes as a spreading code according to their data rates and divides the active users having different representative code split into a number of groups for effective cancellation. At the receiver, The code grouping interference canceller performs cancellation between the groups. The proposed receiver does not require any information about interference users, such as code, data and amplitude, and has relatively low complexity. The results show the large improvement in performance that can be attained by cancellation scheme.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.2
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• pp.190-195
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• 2013

Vacuum circuit breaker(VCB) has been widely used for interruption of load current and fault current for high voltage motor in the industrial field. Its arc extinguishing capability is excellent compared to other breakers. But it has the potential to cause multi reignition surge by high extinguishing capability. Surge voltage is generated by the opening and closing of VCB. Multi reignition surge of VCB is steep-fronted waveform. It may have a detrimental effect on the motor winding insulation. So, most of users install a protection device to limit steep-front waveform at the motor terminal or breaker side. So, most of users install a protection device at the motor terminal or breaker side. This protective device is surge absorber(SA) such as ZnO and RC type. In this study, we analyzed whether there is any effect when two type SA is applied to the VCB multi reignition surge. We confirmed that ZnO SA is slightly more effective than RC SA for reduction of multi reignition surge.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1938-1943
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• 2005

Network human-robot interface is an important research topic. In home application, users access the robotic system directly via voice, gestures or through the network. Users explore a system by using the services provided by this system and to some extend users are enable to participate in a service as partners. A service may be provided by a robot, a group of robots or robots and other network connected systems (distributed sensors, information systems, etc). All these services are done in the network environment, where uncertainty such as the unstable network connection, the availability of the partners in a service, exists. Moreover, these services are controlled by several users, accessing at different time by different methods. Our research aimed at solving this problem to provide a high available level, flexible coordination system. In this paper, a multi-agent framework is proposed. This framework is validated by using our new concept of slave agents, a responsive multi-agent environment, a virtual directory facilitator (VDF), and a task allocation system using contract net protocol. Our system uses a mixed model between distributed and centralized model. It uses a centralized agent management system (AMS) to control the overall system. However, the partners and users may be distributed agents connected to the center through agent communication or centralized at the AMS container using the slave agents to represent the physical agents. The system is able to determine the task allocation for a group of robot working as a team to provide a service. A number of experiments have been conducted successfully in our lab environment using Issac robot, a PDA for user agent and a wireless network system, operated under our multi agent framework control. The experiments show that this framework works well and provides some advantages to existing systems.

• 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.