• Journal of KIISE:Computing Practices and Letters
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• v.13 no.6
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• pp.422-426
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• 2007

Personal mobile devices equipped with non-volatile storage such as MP3 player, PMP, cellular phone, and USB memory require safety for the stored data on the devices. One of the safety requirements is secure deletion, which is removing stored data completely so that the data can not be restored illegally. In this paper, we study how to design the secure deletion on Flash memory, commonly used as storage media for mobile devices. We consider two possible secure deletion policy, named zero-overwrite and garbage-collection respectively, and analyze how each policy affects the performance of Flash memory file systems. Then, we propose an adaptive file deletion scheme that exploits the merits of the two possible policies. Specifically, the proposed scheme applies the zero-overwrite policy for small files, whereas it employs the garbage-collection policy for large files. Real implementation experiments show that the scheme is not only secure but also efficient.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.81-81
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• 2009

최근 휴대폰, 노트북 등과 같은 소형 멀티미디어 기기의 사용이 증가함에 따라 전자 패키징 산업은 경박단소화를 요구하고 있습니다. 더불어 전기적 신호의 손실을 줄이기 위해 전기, 전자산업체에서는 가볍고 굴곡성이 우수한 연성인쇄회로기판(Flexible Printed Circuit Board, FPCB)과 가격이 싸고 신뢰성이 입증된 경성인쇄회로기판(Rigid Printed Circuit Board, RPCB)의 전극간 접합에 많은 관심을 보이고 있습니다. 기존에 연성인쇄회로기판과 경성인쇄회로기판을 접합하는 방식으로는 connector를 이용한 체결법이 사용되고 있지만 완성품의 부피가 커지고 자동화 공정이 힘들며 I/O 개수가 제한적이어서 신호전달에 취약한 단점이 있습니다. 또한, 최근 FPCB를 RPCB에 접합하는데 interconnection으로 이방성 도전 필름(Anisotropic conductive film, ACF) 또는 비전도성 필름(Non-conductive film)이 널리 사용되고 있습니다. 하지만 필름의 가격이 비싸고, 낮은 전기 전도도를 보이며, 신뢰성 특성이 낮다는 단점을 가지고 있습니다. 본 실험에서는 기존의 connector 방식과 접착 필름을 이용한 방식을 대체하기 위하여 솔더를 interlayer로 이용하여 열과 압력으로 접합하는 방법에 대하여 연구하였습니다. 실험에 사용된 솔더의 조성은 Sn-3.0Ag-0.5Cu (in wt%)이고, RPCB와 FPCB의 표면처리는 ENIG로 하였습니다. 접합 온도와 접합 시간에 따라 최적의 접합 조건을 도출하고자 하였고, 접합된 시편을 가지고 신뢰성 테스트를 진행하였습니다. $85^{\circ}C$/85% 고온고습 시험과 고온 방치 시험을 통하여 접합부의 신뢰성을 테스트 하였고, 90도 Peel test로 기계적 접합 강도를 측정하였고, 파괴 단면을 Scanning Electron Microscopy (SEM), Energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS)로 분석하였습니다.

• Korean journal of communication and information
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• v.66
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• pp.159-183
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• 2014

This study analyzed the competition among three game platforms, PC, Console and Mobile in aspect of user's gratifications using niche analysis. To do this, four gratification factors, 'transportability and accessibility', 'liveliness and variety', 'availability and economic feasibility', 'relationship', were assessed. To investigate competition level among three game platforms, niche breadth, niche overlap, competitive superiority of four gratification factors were analyzed. The results of niche analysis show that mobile platform appeared as a most competitive platform because it utilized diverse resources for game user gratification and had competitive superiority in 'transportability and accessibility' which appeared as most important factor determining user's gratification. However there was no game platform which had competitive superiority in all four gratification factors.

• Journal of Digital Contents Society
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• v.17 no.5
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• pp.417-423
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• 2016

Recently smartphone has propagated all age groups rapidly due to the fact that the advance of media and the increase of smartphone penetration. In South Korea, high-school students' smartphone retention rate is 90.2%. This study proceed an analysis of high school students' smartphone usage by a feasibility study, and also by recording the log data of actual usage patterns of smartphone applications. The feasibility study investigates subject's smartphone usage, and the log data analysis measures the accurate usage recorded for about three months. We compared the feasibility study and the log data for the daily smartphone usage, and investigated the change of usage pattern during the weekdays, weekends, and the before, during and after exams. High-school students are unique group in capital area. As a result, we found that high-school students' smartphone usage pattern in capital area has not affected by weekday or weekend but has affected by the before, during and after exams.

• The Journal of the Korea Contents Association
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• v.8 no.9
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• pp.42-54
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• 2008

In recent years, embedded systems have been expanding their application domains from traditional embedded systems such as military weapons, robots, satellites and digital convergence systems such as celluar phones, PMP(Portable Multimedia Player), PDAs(Personal Digital Assistants) to Next Generation Personal Computers(NGPCs) such as eating PCs, wearable computers. The NGPCs are network-based, human-centric digital information devices diverged from the traditional PCs used mainly for document writing, internet searching and database management. Wearable computers with battery capacity and memory size limitations have to use real-time operating systems with small footprints and low power management techniques to provide user's QoS in spite of hardware constraints. In this paper, we have designed and implemented a low-power RTOS (called eRTOS) for wearable computers. The implemented eRTOS has 18KB footprints and the dynamic power management and the device power management schemes are adapted in it. Experimental results with wearable computer applications show that the low power techniques could save energy up to 47 %.

• Journal of IKEEE
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• v.15 no.4
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• pp.324-329
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• 2011

In recent years, the performance and functions of portable devices has increased. so it requires more power efficiency and energy density while using the battery for a long time. therefore Battery pack which are made up from several battery cells in series in order to achieve higher operating voltage is being used. when using a Li-ion battery, we need a protection circuit to protect from overcharge, over discharge, high temperature and over current. Also, when using battery pack, we need to Cell voltage balancing circuit that each cell in tune with the balancing. In this paper, the proposed IC is applicable by mobile devices as well as E-bike, hybrid vehicles, electric vehicles, and is expected to contribute to the development of domestic PMIC.

• Journal of IKEEE
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• v.15 no.4
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• pp.345-353
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• 2011

Recently portable mobile devices such as smart-phones and notebooks have rapidly increasing demands. Those devices consume more power because they are expected to offer more complex functionality including multimedia features. For these reasons engineering efforts are changing to focus on maximizing energy efficiency within a limited battery capacity instead of increasing computational performance. In this paper, we propose a battery management system using event driven programming technique on a embedded processor. We also show that the proposed system satisfies SBS (Smart Battery Specification) v1.1. The proposed system maintains minimum code size and memory size comparing to those of RTOSs. The proposed system can be also easily incorporated in the conventional RTOSs as a form of firmware.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.363-367
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• 1999

As the subscription rate to both Internet services and wireless communications services increases rapidly, traffic in the future wireless communications will be dominated by Internet applications. Current research for wireless technology is focused to the multimedia data transmission mainly for the personal computer or notebook whose display which has large display and abundant memory. But in the near future, Internet access request from the handphone or PDA device which is already spreaded in the world will be large. Special handset terminals which has small display monitor, low capacity memory and poor processing power has to be managed differently from torrent wireless communications protocols. So, WAP Forum is organized with wireless handset manufacturers in the world and the standardization process for wireless application is being actively developed. In this paper, basic model and architecture of WAP is introduced and adaptation requirements for change from HTML documents to WML formats are proposed. Also, compression ratio gained in the transform from the existing web documents to WML is shown.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3A
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• pp.258-264
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• 2009

In this paper, we propose an efficient cooperative diversity scheme for mobile satellite multimedia broadcasting services. The proposed scheme is a transmit diversity technique to adapt time varying channel conditions, and we do not need any channel quality information from the return link. In the proposed scheme, we utilize space-time block coding (STBC) and rate compatible turbo codes in order to realize the transmit diversity for the mobile satellite system with several repeaters. The satellite and several repeaters operate in unison to send the encoded signals, so that the receiver may realize diversity gain. The simulation results demonstrate that the proposed scheme can provide highly improved performance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.05a
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• pp.80-83
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• 2009

The most popular communication protocol is those defined by the IEEE 802.11 WLAN to support broadband internet connection. The demand for real-time multimedia service is increasing through WLAN on the road. The Hand-off function of mobile terminal is essential to support mobility. But, the hand-off function of IEEE 802.11 WLANs has the latency up to 300ms, and recent research has focusing on channel scanning and reconnection to AP and certification process of AP. It is also the lack of consideration in related works that hand-off happens frequently when the mobile node is moving. This paper proposed the hand-off algorithm that guarantees high throughput and estimates the point which may occur hand-off using GPS information and RSSI. We implement the proposed hand-off function that achieves the best performance.