• The KIPS Transactions:PartC
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• v.17C no.3
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• pp.243-250
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• 2010

Vehicular communication networking is one of the most important building blocks of Intelligent Transportation System (ITS). The vehicular communication network is a wireless communication system enabling vehicles to communicate with each other as well as with roadside base stations. Mobility management of vehicles which move at high speeds and occasionally make a long journey is an interesting research area of vehicular communication networks. Recently, The Proxy Mobile IPv6 (PMIPv6) protocol is proposed for network-based mobility management to reduce the overhead of mobile nodes. PMIPv6 shifts the burden of the mobility management from mobile nodes to network agents to decrease the overhead and latency for the mobility management. In this paper, we derive the scenario of deploying PMIPv6 in vehicular communication networks and propose a new LMA handover mechanism for realizing the scenario. By carrying out the ns-2 based simulations, we verify the operability of the proposed mechanism.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6A
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• pp.642-647
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• 2007

HAP(High Altitude Platform) systems have been proposed due to their unique advantages over terrestrial and satellite systems as the alternative wireless communication system to deliver the third generation IMT-2000 wireless services. It has been required to study for the power control in W-CDMA HAP system as well as the terrestrial mobile system in order to mitigate interference and increase the capacity. In this paper, a new power control has been proposed for HAP system considering the interference profile into the DB(distributed balancing) SIR(signal to interference ratio)-based algorithm which has been considered in terrestrial system, and estimated by the outage performance of the proposed DB algorithm is better remarkably than DBPA(distance-based power allocation) which is proposed for HAP system, and it is the same regardless of the antenna maximum gain and its sidelobe characteristics.

• 한국경영정보학회:학술대회논문집
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• 2007.11a
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• pp.309-315
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• 2007

SK텔레콤은 급변하는 이동통신시장 환경의 변화에 적절히 대응하기 위하여 지난 10여 년간 사용해 온 메인프레임 기반의 COIS 시스템을 중단하고 Unix 기반의 NGM 시스템으로 다운사이징하기로 결정하였다. 2002 년 9 월 SK 텔레콤은 차세대 IT 인프라 혁신 전략 프로젝트를 완료하고 이에 근거하여 2003 년 말 1 단계 프로젝트를 추진하게 된다. 그러나 개발 툴의 문제점, Governance 의 확보 실패 등 문제점이 계속 누적되어 2005년에 접어들어서는 총체적 난국 상황에 봉착하게 되었다. 2005 년 2 월 자체 점검 결과 개발 진척도는 50%에 불과한 상황이었다. 결국 2005 년 3 월, NGM 추진본부는 프로젝트의 추진 중단을 선언하기에 이르렀다. NGM 프로젝트는 처음부터 재 검토하여 Re-planning 을 실시한 후 구축을 재개하기로 결정하였다. 2005 년 5 월 NGM 프로젝트의 Re-plan 이 수립되었다. 우선 Turn-key 방식의 문제점을 해소하기 위하여 SK 텔레콤이 구축의 총책임을 떠맡고, SK C&C 가 시스템 이행에 대한 책임을 지는 Governance 체제를 확립하였다. 또한 2 단계 프로젝트에서는 NGM 프로젝트를 기술적으로 원점부터 재 검토하여 이전과는 근본적으로 다른 In-House 구축 접근방식을 채택하기로 하였다. 2 단계 프로젝트에서 관심을 집중한 기술적 의사결정 영역은 크게 (1) 미들웨어 및 개발프레임워크의 적용, (2) DB 아키텍처의 결정 및 슬림화, (3) 시스템 성능 개선 등의 세 분야로 집약할 수 있다. 이 논문에서는 이들 각각의 분야를 구체적으로 검토하였다. 결국 2006 년 10 월 9 일 메인프레임 기반의 COIS 는 Shut-down 되어 가동을 멈추었고, Unix 기반의 NGM 시스템이 가동을 개시함으로써 차세대 마케팅을 본격 추진하기 위한 다운사이징 프로젝트가 성공적으로 완수되었다.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.583-585
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• 2001

이동 단말의 프로토콜 스택을 설계할 때 가장 많이 선호되는 기법은 프로토콜 스택의 계층을 타스크로 정의하고 타스크 사이의 통신을 위해서 매시지 타를 이용하여 하위 계층에서 상위 계층으로 데이터를 전달하는 방식이다. 그러나 3세대 이상의 단말 시스템은 복잡한 응용 프로그램과 운영체제 환경을 가지게 되며 이러한 방식의 설계 방법은 더 이상 효율적이지 않게 되었다. 본 논문은 스트리밍 기술에 기반 한 단말 프로토콜 스택의 설계 방법에 대해서 소개하고 메시지 류 방식에 기반 한 설계 모델보다 가용성이 높음을 보여 준다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.3
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• pp.31-38
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• 2010

In this paper, we have analyzed and compared the BER and the throughput performance through the computer simulation, after applying several MIMO schemes on the MIMO-OFDM system. Then, the throughput performance of the proposed system, Adaptive-MCM, is analyzed. As a result, the MIMO-OFDM Adaptive-MCM system proposed has a higher average data rate than Non Adaptive-MCM system through the improvement of Trade-off problem between throughput and SNR.

• Proceedings of the Korea Information Processing Society Conference
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• 2001.04b
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• pp.627-630
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• 2001

제 3세대 이동통신인 IMT2000에서 단말기는 기존의 통신수단으로서의 역할과 함께 인증, 지불, 로열티 등 다양한 어플리케이션을 이용한 서비스를 가능하게 하는 수단이 될 것이다. 이것을 가능하게 하는 핵심요인은 USIM이라는 IC 카드가 단말기에 내장되기 때문이다. 본 논문에서는 USIM의 구조에 대한 관련 기술과 단말기와 USIM 사이의 프로토콜 형식 및 안전한 지불을 위한 Off-Line 결제 모델을 제안하였다. 제안한 모델은 하드웨어 자체의 제약으로 인해 적절한 크기의 어플리케이션 설계와 효율적인 프로토콜의 설계가 필요하다. 유효성을 입증하기 위해 관련표준을 고찰하였고 썬마이크로 시스템의 Java card 2.1.1 툴킷을 이용하여 시뮬레이션하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3B
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• pp.144-152
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• 2005

Mobile IP(MIP) and SIP have been proposed to support mobility in the wireless internet working at different layers of the protocol stack. However MIP has some problems such as triangle routing, the need of each host's home address, the overhead of tunneling and the lack of wide deployment. Thus we proposed a scheme for supporting mobility based on SIP in this research. A novel SIP system to provide a hierarchical registration has been designed according to this scheme. Our SIP system has been established by implementing JAIN technologies which follow next generation network standards to support the mobility of wireless terminal. This system successfully satisfied ITU-T recommendation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6A
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• pp.458-467
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• 2009

Long Tenn Evolution (LTE) is the next generation mobile phone technology which has being standardized by the Third Generation Partnership Project (3GPP). In the existing mobile communication networks, voice traffic is delivered through circuit switched networks. In LTE, however, all kinds of traffic are transferred through IP based packet switched networks which has best-effort characteristic. Therefore, providing QoS in LTE system is difficult. In order to provide QoS in LTE, RRM is very important. Especially, in part of RRM, call admission control (CAC) performs an important function to reduce network congestion and guarantee a certain level of QoS for on-going calls. In this paper, we propose a CAC algorithm in order to provide QoS for various kinds of services in LTE system. The performance of the proposed algorithm is evaluated with various simulation environments. The results show that the proposed algorithm provides QoS through rejections of requested calls. Especially, the proposed CAC algorithm can be satisfied with packet delay requirement defined in LTE specification.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.6
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• pp.20-26
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• 2008

Today, there are many high speed data access systems that provide the truly "anytime and anywhere" services. Especially, HSDPA (High Speed Data Packet Access), one of the main third generation mobile communication systems, provides 14.4Mbps maximum data throughput. However, HSDPA will fail to provide high data throughput in hostile multipath fading environments due to lack of LOS (Line of Sight). HAPS (High Altitude Platform Station) is one of the solutions to this problem. HAPS system not only provides Los, but it can also provide high data rate services to the conventional terrestrial systems. This paper proposes HAPS-HSDPA system model and compares performance of HSDPA and HAPS-HSDPA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.539-546
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• 2010

In next generation wireless communication systems based on OFDM, multiple-input multiple-output (MIMO) technique is adopted in order to achieve high data throughput with limited bandwidth. As one of MIMO techniques, spatial multiplexing scheme needs high performance data detection algorithm that can be performed with low computational complexity. In this paper, we propose an algorithm that can compute QRM-MLD with reduced complexity. Also, hybrid detection technique is proposed, which can reduce the complexity by selecting between MMSE and QRM-MLD according to the channel condition. The proposed algorithm provides the trade-off between performance and complexity. The computer simulations for downlink transmission in 3GPP LTE system show that less than 0.1dB performance degradation can be achieved at 0.1% BER with 59% reduction on computational complexity compared with the conventional QRM-MLD algorithm.