• Journal of Space Technology and Applications
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• v.4 no.1
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• pp.74-85
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• 2024

As the limitations of conventional radio communications between satellites and the ground become apparent, various experiments are being conducted around the world to overcome them with space laser communication. In this study, we address the development of our own optical communications terminal (OCT) and optical ground station (OGS) and the experiments of free-space optical communication (FSOC) using them. Using a 30 mm-diameter OCT and a 250 mm-diameter portable OGS telescope, as well as commercial 10 Gbps SFP+ modules and media converters, we successfully transmitted and received 4K high-definition multimedia interface (HDMI) signals through 1,550 nm optical laser beam. The transmission and reception distances of the experiment were 3, 9, and 20 km, respectively, and the received signal strength at each distance was +6.1, -2.8, and -10.9 dBm, respectively. It was demonstrated that the 4K HDMI video lasted for over 10 minutes.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.1
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• pp.15-20
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• 2010

This paper proposes a multihoming-based vertical handover scheme using Proxy binding update to minimize handover delay and packet loss while a mobile node moves to a heterogeneous access network. When a mobile node moves to a heterogeneous access network, the proposed scheme can provide a mobile node with fast and seamless handover by performing layer-3 handover using its new interface while the other interface is still communicating in the old access network. The proposed Proxy binding update is different from the Mobile IP binding update in that it includes home addres (HoA) of the old interface instead of the new interface. The performance analysis shows that the proposed scheme can efficiently reduce vertical handover delay and packet loss.

• Proceedings of the Korean Society for Quality Management Conference
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• 2007.04a
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• pp.334-339
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• 2007

인터넷은, 전화로 대변되는 과거의 정보통신 서비스와는 달리 사회 전반에 막대한 영향력을 행사하는 서비스로 발전하였다. 인터넷에 대한 의존도는 향후 모든 정보통신서비스가 인터넷을 기반으로 제공되는 All-IP 디지털 컨버전스 시대에 더욱 더 심화될 것이다. 이 경우 오늘날의 인터넷보다도 QoS(Quality of Service)에 관한 이슈가 더욱 중요해질 것은 자명하다. 이러한 배경에서 ITU(International Telecommunication Union)나 IETF(Internet Engineering Task Force)등의 국제표준화 기구에서 차세대 인터넷 (Next Generation Network, NGN)에 대한 QoS 문제를 연구하고 있다. 그러나 이들 국제기구는 주로 기술공학적인 측면에서 QoS 문제에 접근하고 있어서 현실적으로 완전한 대안을 제공하지는 못하고 있다. 즉, 인터넷 산업의 특성상 사업자간 끊김없는 연동(seamless inter-operations)과 협력이 필수적인데, 이는 기술공학적 측면보다도 비즈니스 및 정책적 관점에서 다루어져야 되기 때문이다. 통신 사업자 및 벤더(vendor)의 글로벌 컨소시엄으로 출발한 TMF(TeleManagement Forum)나 QuEST Forum 등의 역할이 중요해지는 이유가 여기에 있다. 이미 이들 단체는 사업자간 합의에 의해 자발적으로 구축한 NGOSS 및 TL9000 인증시스템을 바탕으로, 망사업자를 비롯한 서비스공급자 및 벤더 등과의 원활한 협력관계를 구축하는 글로벌 de facto 표준을 마련한 바 있다. 본 연구에서는 QoS 보장을 목표로 하는 차세대 인터넷(NGN)의 현실적 성공 가능성을 높이기 위한 글로벌 표준화 노력을 소개하고 이들을 비교/검토한다. 특히, ITU 및 IETF 등의 NGN 개발계획을 비즈니스/정책점 관점에서 보완할 수 있는 TMF와 QuEST Forum의 접근법을 고찰하여, All-IP 컨버전스 환경에서의 QoS 이슈에 시사하는 바를 살펴본다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.6
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• pp.1265-1270
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• 2011

Different wireless technologies have been developed for various mobile applications. To offer seamless service in next mobile communication systems, it needs handoff service between heterogeneous mobile access networks. A high data rate handoff call from WLAN to cellular mobile network can increase rapidly the blocking probability of BS of cellular mobile network. To solve this problem, this paper proposes a new handoff scheme based on user service profiles. The performances of the proposed scheme are evaluated using computer simulations.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.79-82
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• 2007

Recently the diffusion of the advancement of mobile communication technique and mobile terminal increased, The users were demanded seamless services when carrying and moving. It proposed the FMIPv6 (Fast Handoff for Mobile IPv6) from the IETF like this meeting this requirement. The handover procedure of the FMIPv6 causes to defecate with movement detection, new CoA configuration and binding update. But, the delay occurs from each process, when the DAD(Duplicate Address Detection) of the CoA executing, the big delay occurs. This paper proposes a scheme of delay reduction, it omits DAD process and stores in the AR(Access Router) relates in the CoA of the mobile terminal information.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.703-705
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• 2013

외부 데이터베이스를 사용해서 서비스하는 스마트폰 어플리케이션은 네이티브 앱과 모바일 웹을 병행하여 서비스 한다. 일반적인 어플리케이션 환경에서는 외부 데이터베이스에 리소스 및 연산 결과 등의 모든 정보를 담아 두고 접근하여 활용하는 방식을 사용하였다. 반면에 스마트폰 어플리케이션 환경에서 네이티브 앱을 활용하면 디바이스 내부에 외부 데이터베이스의 정보 및 리소스를 저장하여 활용한다. 이 경우 네이티브 앱에서 연산을 수행하고 변경되는 데이터가 발생하면 외부 데이터베이스에 접근하여 업데이트를 수행한다. 그 이유는 병행 접근이 가능한 서비스의 경우 차후에 현재 접근한 네이티브 앱이 아닌 모바일 웹으로 접근하였을 때를 대비해서 최근의 데이터를 항상 유지해야 하기 때문이다. 많은 사용자를 보유한 서비스의 경우 빈번히 발생하는 데이터 업데이트 문제로 많은 자원 소모가 발생된다. 본 논문에서는 앞서 언급한 문제를 해결하고 네이티브 앱과 모바일 웹간의 데이터 연동을 위하여 외부 데이터베이스의 접근을 최소화 하는 기법을 제안한다. 실시간으로 사용자들끼리 정보를 주고받아 상호작용하는 서비스의 빈도가 상당히 낮거나 없는 스마트폰 어플리케이션 환경에서는 서버 접근을 최소화 하는 것이 좋은 방법이다. 제안의 핵심은 네이티브 앱과 모바일 웹의 기본적인 접속 정보만 외부 데이터베이스에 업데이트하여 차후 접속하는 타입이 현재와 다른 경우에만 최근에 변경된 데이터를 외부 데이터베이스에 업데이트하여 서버의 부하를 최소화 하는 것이다. 이 기술을 활용하면 서비스 업체의 경우 서버 유지비용을 낮출 수 있으며 사용자는 빈번히 일어나는 서버와의 통신에 소요되는 비용 및 끊김 현상으로 인한 불편함을 최소화할 수 있을 것으로 사료된다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8B
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• pp.760-767
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• 2009

While network evolution toward all IP based wired and wireless converged network is on the move, services are being progressed into converged and complex services from simply coupled services, and telecommunication operators are developing new technologies which enable users to move between heterogeneous networks without discontinuity of a current service. In this paper, we propose a IP handover mechanism which reduces ping-pong effect during IP handover between WLAN and CDMA2000 1x EV-DO Rev.A neworks. We present stability and enhanced latency of the proposed IP handover mechanism by experimentation. The mechanism was developed under the 3rd phase of BcN project.

• Journal of KIISE:Information Networking
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• v.34 no.4
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• pp.276-286
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• 2007

Existing streaming mechanisms have no consideration for the characteristics of streaming applications because they only consider network stability. In this paper, in order to overcome limitations of the previous work on video streaming, we propose a new video streaming mechanism called "HAViS(Hybrid Approach for Video Streaming)". The proposed mechanism includes more sophisticated features that consider both network and user requirements. Therefore, the HAViS mechanism improves the network stability by adjusting the sending rate of video stream based on the network state and it also provides the smooth playback by preventing the buffer underflow or overflow. Moreover, it is designed to take into consideration the streaming video content. Through the simulation, we prove that the HAViS mechanism efficiently uses the buffer resources and provides improved network stability and smooth playback.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.4
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• pp.115-129
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• 2007

The ubiquitous and autonomic computing environments is open and dynamic providing the universal wireless access through seamless integration of software and system architectures. The ubiquitous computing have to offer the user-centric pervasive services according to the wireless access. Therefore the roaming services with the predefined security associations among all of the mobile devices in various networks is especially complex and difficult. Furthermore, there has been little study of security coordination for realistic autonomic system capable of authenticating users with different kinds of user interfaces, efficient context modeling with user profiles on Smart Cards, and providing pervasive access service by setting roaming agreements with a variety of wireless network operators. This paper proposes a Roaming Coordinator-based security management framework that supports the capability of interoperator roaming with the pervasive security services among the push service based network domains. Compared to traditional mobile systems in which a Universal Subscriber Identity Module(USIM) is dedicated to one service domain only, our proposed system with Roaming Coordinator is more open, secure, and easy to update for security services throughout the different network domains such as public wireless local area networks(PWLANs), 3G cellular networks and wireless metropolitan area networks(WMANs).

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.4
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• pp.168-180
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• 2018

Due to the spread of mobile devices and the introduction of high-quality services, mobile traffic is expected to increase sharply and overload of cellular networks is expected. D2D communication is a way to reduce the load and evolve to 5th generation. Since D2D communication directly communicates between the terminals, it can reduce the overload of the cellular network and improve energy efficiency, data rate and network performance. This paper proposes a D2D handover scheme for D2D communication in cellular networks. The cellular network is a 3GPP EPS, and the proposed D2D handover method improves the existing EPS handover process considering compatibility between existing EPS and D2D communication. We also demonstrate the superiority of the proposed handover scheme using the network simulator ns-3. Simulation results show that the proposed handover scheme is superior to existing handover methods in terms of CUE variation, packet transmission delay time, and throughput.