• ETRI Journal
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• 제37권6호
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• pp.1065-1076
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• 2015

Network densification is regarded as the dominant driver for wireless evolution into the era of 5G. However, in this context, interference-limited dense small cell deployments are facing technical challenges in mobility management. The recently announced results from an LTE field test conducted in a dense urban area show a handover failure (HOF) rate of over 21%. A major cause of HOFs is the transmission failure of handover command (HO CMD) messages. In this paper, we propose two enhancements to HO performance in LTE networks - radio link failure-proactive HO, which helps with the reliable transmission of HO CMD messages while the user equipment is under a poor radio link condition, and Early Handover Preparation with Ping-Pong Avoidance (EHOPPPA) HO, which assures reliable transmission of HO CMD under a good radio link condition. We analyze the HO performance of EHOPPPA HO theoretically, and perform simulations to compare the performance of the proposed schemes with that of standard LTE HO. We show that they can decrease the HOF rate to nearly zero through an analysis, and based on the simulation results, by over 70%, without increasing the ping-pong probability.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 ICEIC The International Conference on Electronics Informations and Communications
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• pp.313-316
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• 2004

This paper presents a new dynamically adaptable polling scheme for efficient support of real-time traffic over an IEEE 802.11 wireless LAN network. The poll scheduling plays an important role in IEEE 802.11 PCF. However, the current version of the polling list management scheme proposed in the IEEE802.11 standard is inefficient when a variable number of mobile stations have variable packets to transmit. If Point Coordinator(PC) has an exact information on the station status, it is possible to efficiently perform polling. In this thesis. we suggest an adaptable polling scheme to meet requirements of the stations. In our scheme, each station transmits packets including a piggyback information to inform that it wants to receive a poll in the next polling duration. Simulation results indicate that our scheme may reduces the packet discard ratio and real-time packet transfer delay.

• International Journal of Internet, Broadcasting and Communication
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• 제10권2호
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• pp.7-12
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• 2018

The spread of IoT (Internet of Things) technology that connects objects based on wired / wireless networks is accelerating, and IoT-based smart home technology that constitutes a super connected network connecting sensors and home appliances existing inside and outside the home is getting popular. In addition, demand for alternative energy technologies such as photovoltaic power generation is rapidly increasing due to rapid increase of consumption of energy resources. Recently, small solar power systems for general households as well as large solar power systems for installation in large buildings are being introduced, but they are effectively implemented due to limitations of small solar panels and lack of power management technology. In this paper, we have studied smart home structure and IoT / IoL device discovery algorithm for energy harvesting system based on photovoltaic power generation, It is possible to construct an efficient smart home system for device control.

• Journal of Communications and Networks
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• 제17권6호
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• pp.568-581
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• 2015

Predicting locations of users with portable devices such as IP phones, smart-phones, iPads and iPods in public wireless local area networks (WLANs) plays a crucial role in location management and network resource allocation. Many techniques in machine learning and data mining, such as sequential pattern mining and clustering, have been widely used. However, these approaches have two deficiencies. First, because they are based on profiles of individual mobility behaviors, a sequential pattern technique may fail to predict new users or users with movement on novel paths. Second, using similar mobility behaviors in a cluster for predicting the movement of users may cause significant degradation in accuracy owing to indistinguishable regular movement and random movement. In this paper, we propose a novel fusion technique that utilizes mobility rules discovered from multiple similar users by combining clustering and sequential pattern mining. The proposed technique with two algorithms, named the clustering-based-sequential-pattern-mining (CSPM) and sequential-pattern-mining-based-clustering (SPMC), can deal with the lack of information in a personal profile and avoid some noise due to random movements by users. Experimental results show that our approach outperforms existing approaches in terms of efficiency and prediction accuracy.

• ETRI Journal
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• 제34권3호
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• pp.341-351
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• 2012

We deal with a resource allocation problem for multimedia service discrimination in wireless networks. We assume that a service provider allocates network resources to users who can choose and access one of the discriminated services. To express the rational service selection of users, the utility function of users is devised to reflect both service quality and cost. Regarding the utility function of a service provider, total profit and efficiency of resource usage have been considered. The proposed service discrimination framework is composed of two game models. An outer model is a repeated Stackelberg game between a service provider and a user group, while an inner model is a service selection game among users, which is solved by adopting the Kalai-Smorodinsky bargaining solution. Through simulation experiments, we compare the proposed framework with existing resource allocation methods according to user cost sensitivity. The proposed framework performed better than existing frameworks in terms of total profit and fairness.

• 한국정보통신학회논문지
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• 제14권2호
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• pp.493-500
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• 2010

XML 웹서비스는 인터넷을 이용한 오픈 네트워크를 통해 단일 또는 다수의 비즈니스 업체 간의 기존 컴퓨터 시스템 프로그램을 결합시키는 표준화된 소프트웨어 기술로서 기업의 수익증대와 비용절감의 효과를 얻을 수 있을 것으로 기대된다. 특히 모바일 매쉬업(Mashup)을 위해서는 XML 웹서비스의 처리가 필수적이다. 본 논문에서는 WIPI 환경과 웹서비스 상에서 사용할 수 있는 XML 파서를 구현하였다. 그리고 HTTP 통신이 WIPI상에서 가능하도록 하여 XML 웹서비스의 서비스 개발에 적용함으로써 모바일 환경에서의 XML 웹서비스 인터페이스를 구현하였다. 유무선 환경에서 동시 사용가능하게 적용한 것은 어떠한 환경에서도 적용 가능한 파서임을 나타낸다. 또한 기존의 파서들과의 성능비교를 통해 제안한 파서가 속도면에서 뛰어난 점을 보여준다. 이에 대한 실제 응용으로서 WIPI용 Java언어를 기반으로 인터넷 서점에 적용하였다.

• 한국정보처리학회논문지
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• 제6권5호
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• pp.1143-1152
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• 1999

A Mobile computing environment is a new paradigm which provides users with the access to information irrespective of users' location. A transaction scheduling method for the mobile computing environment must be designed so that database consistency is maintained with considering the limited performance of mobile hosts and the narrow bandwidth of a wireless network. The scheduling method using a lock has some problems: the high message overhead between a server and a mobile host for maintaining a lock and the high abort ratio of the mobile transactions owing to violating the serializability when a mobile host uses a cache. So, in this paper, we propose an efficient transaction management method using timestamp to resolve these problems. The proposed method is used in the environment under which a mobile host uses a cache having two versions for each cached data item and a server maintains several versions for each data item. So, even though a mobile transaction is executed during several broadcasting interval, can be committed. As a result, the proposed method can improve the commit ratio of the mobile transactions by maintaining multiversion for each data item and does not require the additional message exchange to schedule transactions by using timestamp.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2008년도 춘계 종합학술대회 논문집
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• pp.539-542
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• 2008

무선 센서 네트워크는 에너지 효율 향상과 에너지 비용절감에 기여할 수 있다. 빌딩이나 물류창고 등의 온도 조절기에 문제가 발생한 경우 고가의 에너지가 낭비를 줄이기 위해서는 건물 내부에서 24시간 모니터링 해야 한다. 냉동물류창고의 온도조절기에서 문제가 발생한 경우 에너지 낭비와 더불어 보관되는 물품의 안정성에 치명적인 문제를 발생시킬 수 있다. 본 논문에서는 이러한 문제를 해결하기 위한 방안으로 Zigbee 기술 기반의 물류창고관리 시스템을 구축한다.

• 한국IT서비스학회지
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• 제8권1호
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• pp.193-202
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• 2009

Cloud computing emerges as a new computing paradigm which targets reliable and customizable services. The term builds on decades of research in virtual machine, distributed and parallel computing, utility computing, and more recently networking, web service, and software as a service. In this paper, we provide a seamless connection migration of web services. This is useful for cloud computing environment in which many client terminals have mobility. With the wireless internet facility, those mobile users can move place to place during internet communication. Therefore, we provide solutions to the two major problems in current virtualization based migration: communication failure problems and connection re-establishment. Communication channel flushing by zero window notification helps to resolve the communication failure problems and TCP port inheritance prevents connection re-establishment errors during socket reconstruction. Thus, our web service migration facility is now able to preserve open network connections, and even for server sockets. This is a highly transparent approach, in that we did not Introduce additional messages for channel flushing and did not make any modification to the TCP protocol stack. Experimental results show that the overhead due to connection migration of web services is almost negligible when compared with time to take the conventional web service migration.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 추계학술대회
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• pp.447-450
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• 2010

오늘날 상대적으로 미비한 소규모저수지 및 간척담수호 농업용수의 수질정보를 온라인으로 수집 및 분석하고, 분석된 정보를 실시간으로 전달 및 데이터베이스화함으로써 농업용저수지와 담수호의 수질관리를 체계적으로 할 수 있다. 본 논문에서는 원격에서 자동으로 수질을 측정하고 사용자에게 측정된 정보를 제공하기 위해 각 센서로부터 수집된 정보를 통합 처리 이후 무선 네트워크를 통해서 실시간으로 통합관리 함으로써 관측지점에 대한 수질정보를 실시간으로 모니터링 할 수 있으며 이동 통신망의 이용도 가능한 시스템을 제안하고자 한다.