• Proceedings of the Korea Information Processing Society Conference
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• 2007.05a
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• pp.1199-1202
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• 2007

광대역 무선 액세스 기술에 대한 관심이 증폭되면서, IEEE 802.16 워킹그룹에서는 광대역 무선 도시권 통신망을 정의하였고, 802.16j 태스크그룹에서는 높은 전송 속도와 넓은 커버리지 제공을 위해서 802.16 시스템에 중계기를 도입하는 작업이 진행중이다. 차세대 네트워크 환경에서는 단말의 이동에도 지속적인 서비스를 제공해야 하므로 본 논문에서는 이동 단말과 기지국 간의 통신을 정의하는 802.16e의 핸드오버 절차를 확장하여 802.16j 네트워크에서 단말의 이동성을 제공하기 위한 방안을 정의하고자 한다.

• Proceedings of the Korean Information Science Society Conference
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• 2004.04a
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• pp.844-846
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• 2004

Gnutella Protocol기반 네트워크에서 상호간 통신 및 검색과 응답과정에서 릴레이와 브로드캐스팅 되는 Query메시지들로 인해 많은 통신 부하를 초래한다. 또한 멀티 홉을 통한 질의 응답과정의 통신 오버헤드로 인해 통신 효율성이 저하된다. 따라서 본 논문에서는 Zipf's law 을 기반으로 한 검색어 캐싱기법을 통해, 검색어 및 검색된 응답 문자열의 빈도수와 랭킹, 그리고 검색된 파일의 크기와의 상관 관계를 얻어 캐싱 정책을 수립하고. 이에 따라 캐싱함과 동시에 캐싱정책을 이웃 peer에게 전과함으로써 전체적인 네트웍에서의 P2P응용 성능을 향상시킬 수 있는 캐싱 기법을 제안한다.

• Proceedings of the Korean Society of Computer Information Conference
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• 2012.07a
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• pp.59-61
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• 2012

최근 고정된 네트워크가 아닌 센싱 노드를 기반으로 한 유비쿼터스 센서 네트워크의 관심이 높아지고 있는 추세이다. 센서 네트워크에서는 넓은 지역의 정보 수집이나 망 기반시설이 갖추어 지지 않은 곳의 정보 수집 및 가공과 통신을 위하여 배터리로 구동되는 센싱 노드를 사용한다. 배터리로 구동되는 센싱노드는 통신을 위해 저전력을 사용하기 때문에 근거리 통신만 가능하다. 이러한 거리 제약을 극복하기 위해 멀티 홉 릴레이 기능을 이용한 이동 Ad-hoc 네트워크가 많이 사용된다. 본 논문에서는 이동 Ad-hoc 네트워크에서 운용되어지는 프로토콜과, 기존 망과의 연동을 위해 쓰이고 있는 기술에 대해 알아보고, 이동 Ad-hoc 네트워크상에서의 보안 기술을 고찰 하고자 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8B
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• pp.839-845
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• 2009

The Vehicular Ad-hoc Network (VANET) has two main problems to be overcome due to high mobility and frequently changing density: one is short link duration time and the other is high packet loss ratio. To solve the problems, there have been many studies to predict vehicular mobility. Most of the studies try to enhance link expire time and link reliability, however the distance between two relay nodes becomes too short to have high network throughput. In this paper, we propose a new routing algorithm that considers both link expire time and network throughput in the VANET. The proposed algorithm aims to find path with long link expire time and high throughput. Our simulation results show that the proposed algorithm outperforms the legacy greedy algorithm and its variants.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2B
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• pp.170-177
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• 2009

In this paper, we propose the structures of the NBTC (Narrow-Beam Trisector Cell) and the WBTC(Wide-Beam Trisector Cell) in which directional antennas both at the base station and at the relay station are used. We analyze and compare total capacity of the both systems taking the co-channel interference into consideration for two channel models. Through analysis, we find the effect of LOS (Lind of Sight) path to the total capacity of NBTC structure and that of WBTC structure. Our work may be useful as a guideline to control the interference for the next generation mobile communication and WiBro systems using multi-hop relays.

• Journal of KIISE:Information Networking
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• v.35 no.5
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• pp.437-452
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• 2008

IEEE 802.16j MR networks introduce RSs (Relay Stations) within the IEEE 802.16 system in order to enhance the data throughput and extend the coverage. However, the current standardization defines that the BS (Base Station) controls MS's (Mobile Station's) handover, not only it induces the large signaling overhead but also handover latency could increase. In this paper, we propose a handover protocol in the MR networks where the high capability RSs that can process the MS's control functions are deployed. First, we classify the handover scenarios for the MR networks with the high capability RSs. Then, we define the MAC handover procedure, corresponding MAC management messages and the transmission routes for the proposed messages so that an 802.16e MS can perform seamless handover without noticing it is attached to an MR network. The simulation results show that the proposed handover protocol not only reduces the MAC management message overhead transferred through the wireless links compared to IEEE 802.16j/D1, which is the current standard for MR networks, but also performs the rapider and more secure MS handover than IEEE 802.16e and IEEE 802.16j/D1.

• The KIPS Transactions:PartC
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• v.14C no.7
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• pp.571-582
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• 2007

Vehicular ad-hoc networks is temporarily established through inter-vehicle communication without any additional infrastructure aids. It requires a immediate message propagation because it mainly deals with critical traffic information such as traffic accidents. The distance-based broadcast scheme is one of the representative broadcast schemes for vehicular ad-hoc network. In this scheme, a node to disseminate messages is selected based on a distance from a source node. However, a message propagation delay will be increased if the relay nodes are not placed at the border of transmission range of the source node. In particular, when the node density is low, the message propagation delay is getting longer. In this paper, we propose a time-window reservation based relay node selection scheme. A node receiving the alert message from the source node has its time-window and randomly selects its waiting time within the given time-window range. A proportional time period of the given time-window is reserved in order to reduce the message propagation delay. The experimental results show that the proposed scheme has shorter message propagation delay than the distance-based broadcast scheme irrespective of node density in VANET. In particular, when the node density is low, the proposed scheme shows about 26% shorter delay and about 46% better performance in terms of compound metric, which is a function of propagation latency and network traffic.

• Journal of the Korea Society for Simulation
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• v.18 no.3
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• pp.47-59
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• 2009

Due to the application-specific nature of wireless sensor networks, the sensitivity to such a requirement as data reporting latency may vary depending on the type of applications, thus requiring application-specific algorithm and protocol design paradigms which help us to maximize energy conservation and thus the network lifetime. In this paper, we propose a novel delay-adaptive sensor scheduling scheme for energy-saving data gathering which is based on a two phase clustering (TPC). The ultimate goal is to extend the network lifetime by providing sensors with high adaptability to the application-dependent and time-varying delay requirements. The TPC requests sensors to construct two types of links: direct and relay links. The direct links are used for control and forwarding time critical sensed data. On the other hand, the relay links are used only for data forwarding based on the user delay constraints, thus allowing the sensors to opportunistically use the most energy-saving links and forming a multi-hop path. Simulation results demonstrate that cluster-based delay-adaptive data gathering strategy (CD-DGS) saves a significant amount of energy for dense sensor networks by adapting to the user delay constraints.

• The KIPS Transactions:PartC
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• v.14C no.7
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• pp.597-602
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• 2007

In conventional cooperative communication data rate is 1/2 than non cooperative protocols. In this paper, we propose a full data rate DF (Decode and Forward) cooperative transmission scheme. Proposed scheme is based on time division multiplexing (TDM) channel access. When DF protocol has full data rate, it can not obtain diversity gain under the pairwise error probability (PEP) view point. If it increases time slot to obtain diversity gain, then data rate is reduced. The proposed algorithm uses orthogonal frequency and constellation rotation to obtain both full data rate and diversity order 2. Moreover, performance is analyzed according to distance and optimized components that affect the system performance by using computer simulation. The simulation results revealed that the cooperation can save the network power up to 7dB over direct transmission and 5dB over multi-hop transmission at BER of $10^{-2}$. Besides, it can improve date rate of system compared with the conventional DF protocol.