• Industrial Engineering and Management Systems
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• v.15 no.2
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• pp.131-142
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• 2016

We consider a multi-server queueing system without buffer and with two types of customers as a model of operation of a mobile network cell. Customers arrive at the system in the marked Markovian arrival flow. The service times of customers are exponentially distributed with parameters depending on the type of customer. A part of the available servers is reserved exclusively for service of first type customers. Customers who do not receive service upon arrival, can make repeated attempts. The system operation is influenced by random factors, leading to a change of the system parameters, including the total number of servers and the number of reserved servers. The behavior of the system is described by the multi-dimensional Markov chain. The generator of this Markov chain is constructed and the ergodicity condition is derived. Formulas for computation of the main performance measures of the system based on the stationary distribution of the Markov chain are derived. Numerical examples are presented.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.31-36
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• 2005

Intelligent Space (iSpace) is the space where many intelligent devices, such as computers and sensors, are distributed. According to the cooperation of many intelligent devices, the environment comes to have intelligence. In iSpace, the locations of multiple humans and other objects are obtained and tracked by using multiple camera and color-based method. In addition, we describe a context-aware information system which is based on Spatial-Knowledge-Tags (SKT). SKT system enables humans to access information and data by using spatial location of human and stored information in storage. The proposed tracking method is applied to the intelligent environment and its performance is verified by the experiments.

• Journal of Computing Science and Engineering
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• v.5 no.2
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• pp.141-149
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• 2011

Many distributed and heterogeneous services and devices are accessible in ubiquitous computing environment, so interoperating those services and devices is one of the key tasks in implementing ubiquitous applications. We used to use script languages in integrating such interoperating components and services. However currently available most script languages are not suitable for ubiquitous environment because there are so diverse forms of interoperation targets such as service objects, web, legacy objects and programmable devices. So it is worthwhile designing a new script language well-suited to ubiquitous environment. In this paper, we propose a new script language, called Ubiscript, for the ubiquitous environment. We develop and adopt several unique language features such as remote scope, multiple contexts, web and legacy objects, remote exception handling, etc. in Ubiscript to overcome the limitations of conventional script languages. In this paper, we also describe the implementation of Ubiscript and its runtime system. A couple of ubiquitous applications were developed in Ubiscript, and the applications are tested on the runtime system. According to our experiences and evaluation, Ubiscript turned out to have a high potential in its expression power and contribution to improving ubiquitous application developers' productivity.

• Journal of Digital Contents Society
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• v.14 no.4
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• pp.513-519
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• 2013

In this paper, we provide interfaces according to user application environments and provide tools through web-site that users can create interface to apply a wide range of application environment. HTML5 is used in the creation processing, so users can create various interfaces by dragging mouse and apply it to multimedia, game applications as well as documents by using the ASCII code and key events that are provided in the Android OS. Database of interfaces is stored in HDFS (Hadoop Distributed File System) based on Hadoop for management and users can have their own designed interface or select interfaces through simple login any time. In order to provide interface quickly, HIVE based on Hadoop is used for search and the data is provided in XML file which smart mobile can process quickly.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.4
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• pp.105-112
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• 2011

We propose an adaptive load balancing scheme to transport real-time video streams efficiently in this paper. The playback buffer level of a video requesting client is high or low temporarily in mobile environment. This scheme attempts to allocate more network bandwidth to serve a video request with the lower buffer level preferentially. In this scheme, the amount of network bandwidth is dynamically allocated to the requesting clients according to their playback buffer levels in a distributed mobile system. In order to improve the quality of service and real-time performance of individual video playback, the proposed load balancing scheme tries to maximize the number of frames that are transported successfully to the client prior to their playback times. Fair services can also be provided to all the concurrent clients by making their playback situation more adaptive. The performance of this load balancing scheme is compared with that of other static load balancing scheme through extensive simulation experiments, resulting in the higher ratio of frames transmitted successfully within given deadlines.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.3
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• pp.525-532
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• 2013

Recently. smartphones have been popularized rapidly and now located deep in our daily life, providing a variety of services from banking, SNS (Social Network Service), and entertainment to smart-work mobile office through apps. Such smartphone apps can be easily downloaded from what is known as app store which, however, bears many security issues as software developers can just as easily upload to it. Military apps will be exposed to a myriad of security threats if distributed through internet-basis commercial app store. In order to mitigate such security concerns, this paper suggests a security guidelines for establishing a military-excusive app store and security verification system which prevent the security hazards that can occur during the process of development and distribution of military-use mobile apps.

• The Journal of Korean Association of Computer Education
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• v.10 no.5
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• pp.81-88
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• 2007

To support the movement of a mobile network consisting of several mobile nodes, the IETF NEMO working group proposed NEMO basic support protocol using bi-directional tunneling between the home agent and the mobile router. Since NEMO basic support protocol is based on bi-directional tunneling, all communications to and from mobile nodes are suffer from inefficient routing all the cases. To solve the routing inefficiency problem, several proposals are proposed. However, those proposals results in new problems, such as binding update storm and changes in existing protocol. Especially, binding update storm problem may cause the delay in binding update, this subsequently causes the difficulty for a real time service and the handoff delay on the movement of mobile network. In this paper, we propose a new binding update scheme which reduces binding update latency and the handoff delay through the distribution of the transmission time of binding update messages. The performance of the proposed scheme is also evaluated to demonstrate its efficiency. Simulation results show that the proposed scheme can efficiently reduce the binding update latency.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.249-254
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• 2001

Abstract In this paper, we propose a method of cooperative control based on artifical intelligent system in distributed autonomous robotic system. In general, multi-agent behavior algorithm is simple and effective for small number of robots. And multi-robot behavior control is a simple reactive navigation strategy by combining repulsion from obstacles with attraction to a goal. However when the number of robot goes on increasing, this becomes difficult to be realized because multi-robot behavior algorithm provide on multiple constraints and goals in mobile robot navigation problems. As the solution of above problem, we propose an architecture of fuzzy system for each multi-robot speed control and fuzzy-neural network for obstacle avoidance. Here, we propose an architecture of fuzzy system for each multi-robot speed control and fuzzy-neural network for their direction to avoid obstacle. Our focus is on system of cooperative autonomous robots in environment with obstacle. For simulation, we divide experiment into two method. One method is motor schema-based formation control in previous and the other method is proposed by this paper. Simulation results are given in an obstacle environment and in an dynamic environment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.11
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• pp.3789-3809
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• 2014

Radio environment maps (REMs) and geolocation database represent an important source of information for the operation of cognitive radio networks, replacing or complementing spectrum sensing information. This paper provides a survey of methods for constructing the radio frequency layer of radio environment map (RF-REM) using distributed measurements of the signal levels at a given frequency in space and time. The signal level measurements can be obtained from fixed or mobile devices capable of sensing radio environment and sending this information to the REM. The signal measurements are complemented with information already stored in different REM content layers. The combined information is applied for estimation of the RF-REM layer. The RF-REM construction methods are compared, and their advantages and disadvantages with respect to the spatial distribution of signal measurements and computational complexity is given. This survey also indicates possible directions of further research in indirect RF-REM construction methods. It emphasizes that accurate RF-REM construction methods should in the best case support operation with random and clustered signal measurements, their operation should not be affected by measurements outliers, and it must estimate signal levels comparably on all RF-REM locations with moderate computational effort.

• The KIPS Transactions:PartC
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• v.14C no.4
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• pp.331-340
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• 2007

Mobile network environments are the environments where mobile devices are distributed invisible in our daily lives so that we can conventionally use mobile services at my time and place. The fact that we can work with mobile devices regardless of time and place, however, means that we are also in security threat of leaking or forging the information. In particular, without solving privacy concern, the mobile network environments which serve convenience to use, harmonized without daily lives, on the contrary, will cause a serious malfunction of establishing mobile network surveillance infrastructure. On the other hand, as the mobile devices with various sizes and figures, public key cryptography techniques requiring heavy computation are difficult to be applied to the computational constrained mobile devices. In this paper, we propose efficient PKI-based user authentication and java-based cryptography module for the privacy-preserving in mobile network environments. Proposed system is support a authentication and digital signature to minimize encrypting and decrypting operation by compounding session key and public key based on Korean standard cryptography algorithm(SEED, KCDSA, HAS160) and certificate in mobile network environment. Also, it has been found that session key distribution and user authentication is safety done on PDA.