• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.12
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• pp.1135-1144
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• 2013

Deploying small cells is a reliable and influential solution to handle the skyrocketing traffic increase in the cellular network, and the small cell technology is evolving to ultra-dense network (UDN). In this paper we propose a small cell on/off algorithm with a simple but essential framework composed of access point (AP), user equipment (UE), and small cell controller (SCC). We propose Device-Assisted Networking for Cellular grEening (DANCE) algorithms that save the energy consumption by tying to minimize the number of turned-on APs while maintaining the network throughput. In doing so, SCC firstly gathers the feedback messages from UEs and then makes a decision including a set of turned-on APs and user association. DANCE algorithm has several variations depending on the number of bits of the UE's feedback message (1 bit vs. N bit), and is divided into AP-first, UE-first, or Proximity ON according to the criteria of selecting the turned-on APs. We perform extensive simulations under the realistic UDN environment, and the results confirm that the proposed algorithms, compared to the baseline, can significantly enhance the energy efficiency, e.g., more than a factor of 10.

• The KIPS Transactions:PartC
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• v.14C no.2
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• pp.163-170
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• 2007

The next generation communication environment consists of various wireless access networks with distinct features that are configured as an overlay topology. In the network environments, the frequency of hand overs should be minimized and the error propagation should be solved in order to provide high-quality multimedia services to mobile users. Therefore, we propose an performance enhancement approach, based on mSCTP, that provides high quality multimedia services to mobile users by ameliorating the error propagation problem. We utilizes the following four functions: 1) the separation of transmission paths according to the types of frames. 2) retransmission strategy to minimize the loss rate of frames, 3) Foced vertical handover execution by utilizing bicasting, 4) using the stability period in order to reduce the effect of the ping pong phenomenon. The simulation results show that the proposed approach provides seamless multimedia service to mobile users by achieving error resilience.

• Journal of KIISE:Computing Practices and Letters
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• v.10 no.1
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• pp.75-88
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• 2004

Condor is a distributed batch system for sharing the workload among the computers connected by a network. Condor distributed system was developed on the basis that every machine in a Condor pool is always connected by a network to run a Condor Job. Due to advances in wireless communication and mobile computing technology, conventional distributed computer systems can now include “mobile” clients as well as “fixed” clients. Moreover, mobile users want to lower their power consumption by off-loading potentially power and resource consuming jobs. In this paper, we describe the design and implementation of mobile interface for mobile clients in Condor distributed batch system. The main purpose of this work is to enable users on mobile computers to interact with Condor environment any time anywhere regardless of their connection to a Condor pool. The mobile Condor distributed system also aims to provide mobile users the same Condor services without making any significant changes to the existing Condor system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3675-3681
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• 2009

One of the most important factors in the lifetime of WSN(Wireless Sensor Network) is the limited resources and static control problem of the sensor nodes. In order to achieve energy efficiency and network utilities, sensor nodes can be well organized into one cluster and selected head node and normal node by dynamic conditions. Various clustering algorithms have been proposed as an efficient way to organize method based on LEACH algorithm. In this paper, we propose an efficient clustering algorithm using information entropy theory based on LEACH algorithm, which is able to recognize environmental differences according to changes from data of sensor nodes. To measure and analyze the changes of clusters, we simply compute the entropy of sensor data and applied it to probability based clustering algorithm. In experiments, we simulate the proposed method and LEACH algorithm. We have shown that our data balanced and energy efficient scheme, has high energy efficiency and network lifetime in two conditions.

• The Journal of the Korea Contents Association
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• v.11 no.12
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• pp.639-648
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• 2011

Since the emergence of the smartphone and tablet PC whose wireless internet accessibility has improved, personal computing environment has shifted from PCs to mobile web based mobile devices, and therefore the use of information and the communication method have been changing rapidly. Under the circumstance, domestic universities have actively been establishing mobile websites for smartphone users. Such mobile websites, however, focused on diverse functions and a showy design rather than on usability or accessibility, and were developed simply for the purpose of public relations. For this reason, students are now faced with difficulties in using the websites. Therefore, this paper proposes a novel web interface with the consideration of usability and accessibility in order for users to easily use and assess proper information. The matters to be taken into account in developing a mobile website are an intuitive interface design, user experiences, a user customized interface and compliance with web standards.

• Journal of Korea Multimedia Society
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• v.10 no.4
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• pp.421-431
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• 2007

Due to the rapid development of wireless communication technology, demands on data services in mobile computing environment are gradually increasing. In mobile computing environments, a mobile host began to use cache to overcome the weak point. Caching at mobile host could reduce the bandwidth consumption and query response time, but mobile host must maintain cache consistency. In this paper, we propose a cache consistency strategy to consider the period of data usage. The server allows an effective broadcasting by classifying data into two groups of periodic and non-periodic. By classifying the data, it prevent from elimination of cache after disconnection of periodic data by using expired time. By storing IR(Invalidation Report) messages, this scheme divides cached data by selection after disconnection. Consequently, we have shown much improvement in total consumption of bandwidth than the conventional scheme.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.1
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• pp.364-370
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• 2011

The Hilbert transform performs a role to transform band pass signals into low pass signals in wireless communication systems. The operation of Hilbert transform is based on a convolution process which is required adding and multiplying calculations. When the Hilbert transform is designed and hardware-implemented at gate level, the adding and multiplying operation requires a high power consumption and a occupation of wide area on a chip. So the results of adding and multiplying operation cause to degrade the performance of implemented system. In this paper, the new Hilbert transformer is proposed, which has a low hardware complexity by application of MAG(Minimum Adder Graph) algorithm. The proposed Hilbert transformer was simulated in ISE environment of Xilinx and showed the reduction of hardware complexity comparing with the number of gate in the conventional Hilbert transformer.

• Journal of KIISE:Information Networking
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• v.37 no.2
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• pp.99-108
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• 2010

The Wireless Ad Hoc network is discussed as a core technology for ubiquitous computing, and the smart tag technology is currently being actively discussed as a part of the sensor network. Thus, considering its security may advance the realization of ubiquitous computing. RFID (Radio Frequency Identification) technology using the smart tag technology as a part of the sensor network is currently in the limelight. In particular, when RFID is applied to a knowledge management system managing various data, data mobility and management convenience are ensured and automated knowledge service can be provided to users. Accordingly, this paper to proposed a secure scheme for mobility knowledge management systems using multi-agents differentiated from the existing knowledge management systems. Specifically, the proposed scheme designates user's authentication and privilege information in multi-agents and provides effective knowledge service through grouping based on user information. Moreover, even user's movement, the proposed scheme ensures service availability and provides continuous information through communication with multi-agent systems.

• Journal of Korea Multimedia Society
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• v.13 no.8
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• pp.1163-1170
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• 2010

In this paper, in order to develop a remote progress management system through the Internet, we show a design method to make easy maintenance by developing the system with both the JAVA language and GoF Design Patterns. For the system implementation, we added the RS232C and RS422/RS485 communication modules to PLC(Programmable Logic Controller) in the control box which provide the real time status data of machines. Also we set up the RS232C to Ethernet converter based on wireless environment to communicate the PLC control data. We use JAVA Swing components to implement the multi-tier architecture system supported the GUI of the Applet and Frame at the same time so that the manager grasps the progress of work easily at the remote machines through the Internet. The key objective of the multi-tier architecture is to share resources among clients, this proposed system can help to develop the software to control the remote machine, and also it has the advantage that developer who wants to make a similar software can make easy to add new function reusing the existing codes.

• Journal of Navigation and Port Research
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• v.30 no.3 s.109
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• pp.189-195
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• 2006

Sea operation monitoring system is a system for the automatic ship operation that is used on the variety sea operations such as laying optical cables on the sea between the countries, laying cables on the seabed for a remote island, laying pipelines for the natural gas, and so forth. This system processes data which obtained through setting up environment and input from several sensors, and display GPS information with ENC data. And this system processes not only data of route file about sea operation, but also realtime information from PDA of client wirelessly connected with AP on wireless LAN. In addition, this system can improve efficiency of the operation as a result of enabling free movement within valid range. This paper design and implementation monitoring system from above appropriate to the embedded system, and improve competitive power of ship through prevention of a ship accident, to keep minimizing operation loads and support both the automatic ship operation and the safety voyage.