• The KIPS Transactions:PartD
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• v.15D no.1
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• pp.131-138
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• 2008

This paper describes the implementations of the first application service based on embedded Linux; Mobile Teller which uses WiBro network for data communications and CDMA network for voice communications. Currently, with the appearance of WiBro service, dual-mode terminals which support two heterogeneous networks are available. But, the development of applications which effectively use these networks for providing better service to user is rarely prepared. At Mobile Teller, when a sender on a dual-mode terminal types texts, the texts are transmitted to a TTS server located in the Internet through WiBro network. Subsequently, the TTS server converts the texts into voices and transmits the voice data to the dual-mode terminal. At last the dual-mode terminal sends the voice to the receiver through the CDMA network. In case of noisy environment or when a user has difficulty in speaking, Mobile Teller makes voice communication possible

• Proceedings of the Korean Information Science Society Conference
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• 2006.06d
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• pp.184-186
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• 2006

일반적인 IP 네트워크에서 이동성을 보장해 주는 대표적인 기술인 Mobile IP 에서는 핸드오버에 따른 패킷 유실의 문제를 피할 수 없다. 따라서 이러한 패킷 유실의 문제를 해결하기 위한 대안으로 Smooth Handover가 제시 되었다. 하지만 Smooth Handover의 경우 핸드오버 동안의 패킷 버퍼링과 핸드오버에 따른 패킷 순서 뒤바뀜의 문제가 발생하고 결과적으로 전체 네트워크의 성능이 감소하는 결과를 초래한다. 차세대 휴대 인터넷 기술인 와이브로(Wireless Broadband Internet. WiBro) 시스템에서도 역시 서비스 중인 단말이 핸드오버 시 동일한 문제가 발생한다. 특히 와이브로 시스템은 휴대성과 이동성을 보장하고 IEEE 802.16 표준을 기반으로 서비스 클래스에 따른 차별적인 서비스를 제공한다. 따라서 패킷 순서 뒤바뀜 문제를 해결하는 핸드오버 메커니즘이 휴대인터넷에서 필요하다. 본 논문에서는 와이브로 시스템에서 고속으로 이동 중인 단말이 핸드오버 시 발생할 수 있는 패킷 순서 뒤바뀜 문제를 해결하는 핸드오버 메커니즘을 제안 한다.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.441-444
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• 2006

통신기술의 급격한 발전, 유비쿼터스에 대한 시장수요 증가, 신규 시장창출을 위한 비즈니스 전략이 결집되어 유무선 융합의 패러다임이 전개되고 있으며 유선의 전송속도와 무선의 이동성을 결합한 와이브로는 유무선 융합을 주도할 서비스로 부각되고 있다. 2006년 상반기에 상용화 될 예정인 와이브로가 안정적인 가입자 기반으로 조기에 시장확산을 이루기 위해서는 동시기에 출시될 HSDPA에 비하여 차별적 지위를 확보하고 기존 서비스와의 관계를 정립하기 위한 포지셔닝 전략이 요구된다. 이에 본 연구에서는 소비자 설문조사를 통해 와이브로의 시장수요를 HSDPA와의 관계 분석을 바탕으로 전망하며 기존 서비스와의 대체 또는 보완 관계를 파악하여 와이브로의 시장위상을 예측하였다. 분석결과 첫째, 잠재적 이용자가 인식하는 와이브로의 서비스 역량은 HSDPA에 비하여 전송속도와 이용요금에서 차별적 우위를 나타냈으며 둘째, 와이브로는 HSDPA에 비하여 가입자 규모에서 상대적인 우위를 보였으며 두 서비스의 가입 영향요인은 상이하였다. 마지막으로 와이브로는 초고속인터넷과는 보완 관계를, 이동전화 무선인터넷과 공중 무선랜과는 대체 관계를 형성하는 것으로 나타났다.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.6
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• pp.823-829
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• 2011

This paper covers the service quality of packet-based voice service that is provided over a wireless broadband (WiBro) network. Using a measurement software that has been developed in the course of preparing a advanced service quality management scheme for the packet-based voice service over a wireless network[2][3], a huge scale of experiment is conducted to measure the real quality of the voice service. Based on our analysis of the measurement result, the service quality of the voice service is supposed to be quite good over WiBro networks. In addition, another experiment to investigate the effect of degradation of wireless transmission conditions on the service quality of the voice service shows the values of wireless service metris in which mean opinion score (MOS) starts to decrease.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.3
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• pp.91-99
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• 2009

Development of high-speed Internet services and the increased supply of mobile devices have become the key factor for the acceleration of ubiquitous technology. WiBro system, formed with lP backbone network, is a MBWA technology which provides high-speed multimedia service in a possibly broader coverage than Wireless LAN can offer. Wireless telecommunication environment needs not only mobility support in Layer 2 but also mobility management protocol in Layer 3 and has to minimize handover latency to provide seamless mobile services. In this paper, we propose a fast cross-layer handover scheme based on signal strength prediction in WiBro environment. The signal strength is measured at regular intervals and future value of the strength is predicted by Exponential Smoothing Method. With the help of the prediction, layer-3 handover activities are able to occur prior to layer-2 handover, and therefore, total handover latency is reduced. Simulation results demonstrate that the proposed scheme predicts that future signal level accurately and reduces the total handover latency.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.6
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• pp.719-726
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• 2014

This paper addresses quality of experience(QoE) and how to measure and evaluate QoE including its subjective aspects. Adopting the real measurements on the field, a various quality metric have been measured for VoIP(voice over IP) service provided through a wireless interface of WiBro(Wireless Broadband). By analyzing the measured values and correlation between the metrics, we attempt to find a method to evaluate QoE of the VoIP service in a objective way. As a result, it has been shown that QoE of the VoIP service through WiBro network has close relation to the packet-level end-to-end delay, and the delay has close relation to received signal strength indicator(RSSI).

• The KIPS Transactions:PartC
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• v.15C no.4
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• pp.263-272
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• 2008

Recently, WiBro has been developed to efficiently support real-time broadcasting with wireless system. MBS (Multicast Broadcast Service) based on WiBro has numerous applications such as DMB. Since the current MBS uses only common channel managed by scheduling, it cannot effectively support many users at the same time. This paper proposes a new counting scheme with which the channel mode can be properly switched between common channel and dedicated channel. It thus allows efficient use of limited radio resource in WiBro for the MBS.

• Information and Communications Magazine
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• v.25 no.4
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• pp.62-66
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• 2008

지난 2007년 진행되었던 와이브로 기술의 IMT-2000 표준화 과정을 되짚어 봄으로써 와이브로 기술에 제기된 의문점들이 무엇 인지와 이를 어떻게 극복했는지를 살펴보고, 이를 통해 앞으로 예상되는 IMT-Advanced 등의 국제 표준화 과정에서 준비해야 할 일들에서 고찰해보고자 한다.

• Journal of Digital Contents Society
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• v.14 no.4
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• pp.471-479
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• 2013

WiBro technology provide mobile devices with a transmission speed of more than 1 Mbps even under the condition of high mobility (120 km/h). In a building, however, there is more demand for high bandwidth for various activities, and WiBro services may not be available. In order to guaranteeing a seamless service continuity and high transmission capability for mobile users within a specific establishment that has deployed WiBro network, we should secure an internetworking platform for WiBro and WiFi networks. This paper introduces WiMax forum and 3GPP standards, proposes WiBro-WiFi Interworking (WWI) architecture, its implementation details, and finally verifies validity of the proposal by using OPNet simulations.

• The KIPS Transactions:PartD
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• v.15D no.2
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• pp.257-262
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• 2008

This paper describes the implementations of the application service based on embedded Linux; Personal Audio Recorder (PAR) which uses WiBro network for data communications and CDMA network for voice communications. At PAR, when PAR client starts voice recording on a dual-mode terminal, the CDMA voice data of caller and callee is transmitted to storage server located in the Internet through WiBro network. Then, PAR server stores voice data on storage server according to the call number and call time. In case of shortage of storage space on terminal, PAR makes user to store voice data. And, PAR can search a catalog of stored data on server and play the specific content.