• Proceedings of the Korean Information Science Society Conference
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• 1999.10c
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• pp.661-663
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• 1999

무선 ATM 환경에서 이동단말기의 이동성을 지원하기 위한 핸드오버방식인 VCT 핸드오버방식은 트리개념을 도입하여 이동단말이 이동할 수 있는 구역내의 모든 기지국에 대하여 사전에 모든 연결을 설정하는 방식으로서, 신속한 핸드오버가 가능하고, 핸드오버 후에도 QoS를 쉽게 보장할 수 있다는 장점이 있으나, 망 자원의 사용면에서 비효율적인 문제점을 갖고 있다. 따라서, 본 논문에서는 이동단말의 이동성을 고려하여 이동이 예상되는 셀에 대해서만 미리 자원을 예약함으로써 불필요하게 예약되는 자원의 낭비를 줄일 수 있는 방안에 대해 제시하고, 이에 대한 성능을 평가하고자 한다.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.4
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• pp.52-60
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• 2008

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.6
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• pp.1208-1216
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• 2015

In this paper, we use WiMedia WLP-based networks to meet the demand for IT services of a ship. If a mobile node moves to a congested base station of a new subnetwork, we will propose a scheme for improving performance of radio link of existing communicating mobile nodes. An old base station denotes packets stored during a handover. And, a proposed buffer management determines to discard the buffered packets in accordance with congestion degree at the congested new base station. Simulation results show that the proposed buffer management scheme improves link utilization in congested wireless links.

• Journal of the Korea Society of Computer and Information
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• v.14 no.3
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• pp.103-111
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• 2009

IEEE 802.16e(Wibro) standard, providing robust mobile realtime data transmission technology, requires of faster and smooth execution of security mechanisms, such as key distribution and user authentications, during base station hopping. In particular, key management mechanisms such as redistribution and regeneration have an impact on digital contents transmission and realtime data transmission, not only in 802.16e environment, but also in typical transmission environment as well. This paper presents traffic management mechanisms designed to realtime digital contents (such as IPTV) transmission efficiency and increase the QoE by utilizing OKTEK methodology.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5A
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• pp.294-304
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• 2003

For an efficient software download in cellular CDMA systems, session admission control based on area (SACA) is presented. In the SACA scheme, the base station only allows mobile terminal to start session when the mobile locates near the base station of a cell. A mobile that is located near cell center can request software download session, but the mobile that is far away from the center can request session only after arriving near the cell center. Session duration time follows exponential and Pareto distribution. Performance is analyzed in terms of handoff rate, mean channel holding time, session blocking probability and handoff forced termination probability. As analysis results, handoff rate between cells in the proposed scheme is reduced to 30 ~ 250 % compared to conventional scheme, according to traffic characteristics such as terminal speed, session duration time and the size of the allowable zone area in a cell for the start of the session. And new session blocking probability slightly decreases to 5 ~ 20 %, but handoff session forced termination probability drastically decreases to 35 ~ 220 %.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4C
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• pp.353-364
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• 2002

To prevent the performance degradation of TCP due to packet loss in the smooth handoff by the route optimization extension of Mobile If protocol, a buffering of packets at a base station is needed. A buffering of packets at a base station recovers the packets dropped during the handoff by forwarding the buffered packets at the old base station to the mobile user. But, when the mobile user moves to a new foreign network which is connected to a congested router, the buffered packets forwarded by the old base station are dropped and the link utilization performance degraded due to increased congestion by the forwarded packets. In this paper, when the mobile user moves to a new foreign network which is connected to a congested router, Ive propose a packet forwarding control scheme required far the old base station to improve TCP performance in mobile networks. The old base station forwards or discards the buffered packets during handoff by proposed packet forwarding control scheme based on congestion states of RED(Random Early Detection) at the congested router. Simulation results slow that link utilization performance can be improved by applying proposed packet forwarding control scheme.

• Journal of Korea Multimedia Society
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• v.11 no.7
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• pp.1016-1024
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• 2008

In this paper, we designed and implemented the ACE(ACtive Emergency call service system) system for emergency call service actively. ACE system has two physical components; E-Device(Emergency Mobile Device) and E-Server(Emergency Server). The role of E-Device is the mobile device in order to call emergency by using mild handi-capped, the elderly and children who are able to communicate theirs intention to another. E-Server is the server for management E-devices with realtime monitering. E-Device will be developed to the portable size for easily mild handi-capped, the elderly and children. When they need the service of emergency call, the button of E-device can be used and the call signal is transmitted to the emergency office and the guardian through Internet and CDMA. E-server should be developed the integrated control system for management of E-Devices basically. And it also supported to realtime monitoring of E-devices with respect to high quality of emergency call service for rise the efficiency.

• Proceedings of the Korea Information Processing Society Conference
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• 2013.11a
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• pp.253-256
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• 2013

Device-to-device (D2D) 통신 기술은 기지국 및 Access Point (AP)와 같은 인프라의 경유 없이 트래픽 교환이 단말기간에 직접적으로 이루어지도록 하는 기술이다. 오늘날 D2D 통신 기술은 셀룰러 망 과부하 문제의 해결책으로써 많은 관심을 받고 있다. 본 논문에서는 대표적인 D2D 통신 기술인 Wi-Fi Direct에 기반하여 형성된 네트워크에 존재하는 다수의 단말에게 동영상을 스트리밍하기 위한 안드로이드 라이브러리 개발 사례를 소개한다. 본 논문에서 소개하는 라이브러리는 의사 브로드캐스트(Pseudo-broadcast) 방식을 사용하여 다수의 단말에게 동영상을 스트리밍한다. 의사 브로드캐스트 방식은 빠른 전송 속도로 동영상을 스트리밍할 뿐만 아니라 한 번의 전송을 다수의 단말에게 동일한 데이터를 전송할 수 있는 장점이 있다.

• Journal of the Institute of Convergence Signal Processing
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• v.6 no.2
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• pp.95-99
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• 2005

This paper presents an accurate recovery method of the reference clock which is needed for network synchronization in two-way satellite multimedia systems compliant with DVB-RCS specification and which use closed loop method for burst synchronization. In these systems, the remote station transmits TDMA burst via return link. For burst synchronization, it obtains reference clock from program clock reference (PCR) defined by MPEG-2 system specification. The PCR is generated periodically at the hub system by sampling system clock which runs at 27MHz $\pm$ 30ppm. Since the reference clock is recovered by means of digital PLL(DPLL) using imprecise PCR values due to variable random jitter, the recovered clock frequency of remote station doesn't exactly match reference clock of hub station. We propose a robust recovery method of reference clock against random delay jitter The simulation results show that the recovery error is remarkably decreased from 5 clocks to 1 clock of 27MHz relative to the general DPLL recovery method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.8
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• pp.681-687
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• 2014

Internet traffic is rapidly increasing due to the spread of personal smart devices. It causes serious burden on base stations and access points which are installed in buildings, buses, trains, and ships. We consider a communication scenario aboard a cruise ship and propose efficient contents distribution schemes to alleviate the burden of access points with multi-device-to-multi-device(MD2MD) communication. The proposed transmission method is based on the hybrid STBC-SM scheme. We compare the error performance of MD2MD communication system on the cruise ship using space-time block coding (STBC) scheme, spatial multiplexing (SM) scheme. The proposed MD2MD communication system is expected to adopt in the ship-area-network (SAN) with efficient contents distribution and reliable communication.