• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.263-267
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• 2006

OFDM(A) 기반 네트워크는 IEEE 802.16e 시스템 및 WiBro 시스템 등으로 구현되고 있으며, 4G 시스템과 같은 차세대 이동통신 시스템의 기반 기술로서 많이 연구되고 있는 시스템이다. 이와 같은 OFDM(A) 시스템을 기반으로 IP 네트워크를 구축하게 된다면, 단말의 핸드오버를 지원하기 위하여 MAC 및 IP 계층에서의 핸드오버 기법에 대한 정의가 필요하다. IP 네트워크의 가장 큰 특징은 CDMA와 같은 서킷 네트워크가 아니라 패킷 네트워크라는 것이다. 이러한 패킷기반 네트워크에서의 소프트 핸드오버 기법은 CDMA 네트워크에서 제공되고 있는 소프트 핸드오버 기법을 그대로 적용할 수 없다. CDMA 소프트 핸드오버 기법은 물리계층에서의 신호 결합을 수행하게 되는데 패킷 네트워크에서 두 기지국으로부터 전송되는 패킷은 MAC 및 IP 헤더를 가지게 되고, 헤더에 포함되는 정보는 각 기지국에서 서로 다르게 전송하므로 물리계층에서의 신호 결합을 수행할 수가 없다. 본 논문에서는 기존에 제안된 소프트 핸드오버 기법의 단점을 보완하고 IP 기반 네트워크에 적용 가능한 소프트 핸드오버 기법을 제안한다. 제안하는 소프트 핸드오버 기법은 패킷 네트워크의 특성을 반영하여 소프트 핸드오버에 참여하는 기지국이 서로 다른 패킷을 전송하도록 디자인하였고, 에러 발생률을 낮추기 위하여 AMC (Adaptive Modulation and Coding) 기법을 적용하였다. 또한 OFDM(A) 시스템의 multi-carrier 특성을 이용하여 네트워크 자원을 효율적으로 사용함으로써 네트워크의 전체적인 성능 향상이 가능하도록 개발되었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9B
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• pp.857-866
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• 2009

Recently, IP mobility study of infra's common elements is undergoing processes to achieve FMC based on All-IP. Existing typical mobility technology based on IP is IETF's Mobile IP. However, it faced to limitations due to packet loss, delays when MN is moving on Mobile IP, also existing network infra - routers (FA)-needed to add/change the functions to support Mobile IP. In this paper, existing mobility problems based on IP and the suggested improvements for platforms which support mobility, quality, security are proposed. It discusses the performance on the current existing IP infrastructure derived from simulation analysis on mobility packet loss and delay. From the resulting data, improvements will also be outlined for optimal performance.

• Journal of KIISE:Information Networking
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• v.36 no.3
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• pp.204-211
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• 2009

Proxy Mobile IPv6(PMIPv6) is that network-based mobility management protocol that network supports mobile node's mobility on behalf of the Mobile Node(MN). In PMIPv6 network, data packets from a Correspondent Node(CN) to a MN will always traverse the MN's Local Mobility Anchor(LMA). Even though, CN and MN might be located close to each other or within the same PMIPv6 domain. To solve this problem, several PMIPv6 Route Optimization(RO) schemes have been proposed. However, these RO schemes may result in a high signaling cost when MN moves frequently between MAGs. For this reason, we propose an adaptive route optimization(ARO) scheme. We analyze the performance of the ARO. Analytical results indicate that the ARO outperforms previous schemes in terms of signaling overhead.

• Journal of the Korea Society of Computer and Information
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• v.13 no.5
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• pp.85-94
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• 2008

As a variety of wireless network services, such as WLAN, WiBro, cdma2000, and HSDPA, are provided and the range of users' choices for the wireless services are broaden, MCoA (Multiple Car-of Address) concepts that enable users to use wireless interfaces simultaneously have been presented in IETF MONAMI6 WG. Through this scheme, users can access several networks simultaneously by using multiple wireless interfaces. Such various wireless connection technologies continue to advance as they are connected and integrated to All-IP-based core network, and at the same time, heterogeneous networks are being managed overlaid according to the coverage of the wireless connection technologies. Under such circumstances, needs for an integrated architecture have arisen, and thus Wireless service framework is required that effectively manages heterogeneous networks which coexist with next generation's networks for 4G. In this paper, a wireless service framework is suggested in the consideration of current wireless service environment, and the framework covers the schemes to minimize the packet loss caused by handover, and also modified Multiple Care-of Address that helps to select most effective network by considering characteristics of various interfaces as well as users' preferences.

• The Transactions of the Korea Information Processing Society
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• v.4 no.7
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• pp.1804-1820
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• 1997

In this paper, an efficient call control procedure is presented for next generation wireless ATM networks and its performance is mathematically analyzed using the open queueing network. This procedure is based on a new scheme called as the cell clustering. When we use the cell clustering scheme, at the time that a mobile connection is admitted to the network, a virtual cell is constructed by choosing a group of neighboring base stations to which the call may probabilistically hand over and by assigning to the call a collection of virtual paths between the base stations. Within a microcell/picocell environment, it is seen that the cell clustering can support effectively a very high rate of handovers, provides very high system capacity, and guarantees a high degree of frequency reuse over the same geographical region without requiring the intervention of the network call control processor each time a handover occurs. But since mobiles, once admitted, are free to roam within the virtual cell, overload condition occurs in which the number of calls to be handled by one base station to exceed that cell site's capacity of radio channel. When an overload condition happens, the quality of service is abruptly degraded. We refer to this as the overload state and in order to quantify the degree of degradation we define two metrics, the probability of overload and the normalized average time spent in the overload state. By using the open network queueing model, we derive closed form expressions for the maximum number of calls that can be admitted into the virtual cell such that the two defined metrics are used as the acceptance criteria for call admission control.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.2
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• pp.54-67
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• 2000

It is known that the performance of a DS-CDMA system mainly depends on Multiple Access Interference(MAI). The effect of MAI in a reverse link is larger than that of a forward link because of the absence of orthogonality among mobile stations. In this paper we investigate the effect of synchronous transmission in the reverse link, which is compared to the performance of asynchronous transmission in the reverse link. In addition, we consider the effect of interference from Mobile Stations(MSs) in a hand-over region. That is, if we assume that a MS is moving from a serving base station(sowing BS) to a target base station(target BS), the signal of the MS is not orthogonal with the signals of all other MSs within the target BS because the MS is only synchronized with the serving BS. Finally we suggest an interference cancellation scheme to reduce the interference from MSs in the region of hand-over, which can be one of solutions for the capacity degradation due to interference from the MSs in the hand-over region in reverse link synchronous transmission.