• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.5
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• pp.47-53
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• 2007

The purpose of IEEE 802.16j is to extend coverage and to enhance throughput by using relay station additionally to conventional IEEE 802.16e . The cellular system experiences performance degradation at the cell edge due to pathloss, shadow and multipath fading. We can get advantage of spatial diversity gain by using relays more than two cooperatively in the IEEE 802.16j system. Cooperative relaying using space-time code provides better performance under multipath fading and has more robustness against the shadow fading than single relaying. In this paper, we investigate the performance of IEEE 802.16j using cooperative relaying by link level simulation. We also show that the cooperative relaying system achieves better performance than the conventional single relaying system. We apply realistic shadow model considering correlations between shadow fadings of different relaying paths. It is shown that the performance of the system depends highly on the spatial location of relay stations.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.535-538
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• 2005

Wireless LANs based on the IEEE 802.11 standard are widely spread for use nowadays. Traffic which are conveyed over the WLANs change rapidly from normal data such a Email and Web pages, to multimedia data of high resolution video and voice. To meet QoS (Quality of Service) required by these multimedia traffic, the IEEE 802 committee recently has developed a new standard, IEEE 802.11e. IEEe 802.11.e contains two MAC mechanisms for providing QoS: EDCA(Enhanced Distributed Channel Access) and HCCA (HCF Controlled Channel Access). Using these standardized MAC mechanisms as a building platform, various admission control mechanisms can be combined to offer QoS gurantees for multimedia traffic. This paper surveys these research efforts.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10c
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• pp.553-555
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• 2002

인증(Authentication)과 암호화 키(Key) 운용 방법론은 통신 서비스 고려시 소홀할 수 없는 중요한 문제이다. 현재 가장 널리 보급되어 사용중인 IEEE 802.11 기술에서도 이와 같은 보안 지원에 문제가 있음이 명백히 드러나고 있다. 포트 컨트롤을 통하여 접속 지점에서부터 통신을 제어하는 IEEE 802.1X는 이를 위한 적절한 보안 해결책이 되고 있고, IEEE 802.11 WGi는 802.1X를 기초로 하는 RSN(Robust Security Network)울 위한 표준화가 진행중이다. 그러나 IEEE 802.1X 프레임워크에서 상호 인증과, 키 분배 및 갱신 정책은 채택하는 인증 프로토콜에 강하게 의존하는 약점을 가지고 있다. 따라서 본 논문에서는 UMTS 보안 아키텍처의 인증 토큰(Authentication Token)을 추가하여 IEEE 802.1X 프레임워크에 상호 인증 및 키 갱신 구조를 포함하도록 하였다.

• Journal of Internet Computing and Services
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• v.13 no.1
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• pp.7-14
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• 2012

In this paper, performance of IEEE 802.11 carrier-sense multiple access with collision-avoidance (CSMA/CA) protocols in saturated traffic conditions is presented taking into account the impact of imperfect channel sensing. The imperfect channel sensing includes both missed-detection and false alarm and their impact on the performance of IEEE 802.11 is analyzed and expressed as a closed form. To include the imperfect channel sensing at the physical layer, we modified the state transition probabilities of well-known two state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model. Based on both theoretical and simulated results, the probability of detection is concluded as a dominant factor for the performance of IEEE 802.11.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.6
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• pp.112-120
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• 2009

Both security enhancement in wireless and fast access for mobility are required to employ wireless LAN in ITS (Intelligent Transportation Systems). However, for the case of employing IEEE 802.11i security standard, it is known that the user authentication procedure of IEEE 802.1x and 4-way handshake procedure for stronger security enforcement may not be suitable for ITS due to its large delay. In this paper, we propose fast authentication method to resolve the above authentication delay problem, and verify its performance via simulation analysis.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.12
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• pp.1359-1364
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• 2014

IEEE 802.11p is a representative PHY/MAC layer standard in vehicular communications. The performance of IEEE 802.11p based communication systems has been measured in various criterions such as link setup time, error rate, and throughput for the case of one-to-one. In this paper, we measure the performance of IEEE 802.11p based communication systems in large capacity transmission. The performance of large capacity transmission is measured by considering the maximum 32 simultaneous transmission including one-to-one transmission. We consider two transmission schemes, i.e., broadcasting and unicasting, and the performance is represented as the receiving rate and throughput.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.1
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• pp.37-41
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• 2018

In this paper, we evaluate the power consumption of IEEE802.15.4e TSCH which uses the specific link scheduling scheme proposed in reference[1]. And we also compares it with the power consumption of conventional single channel IEEE802.15.4. The power consumption of IEEE802.15.4e TSCH is smaller than the conventional one under the any conditions of traffic. The reasons can be explained as the followings. Firstly, TSCH does not have backoff time because of using the collision free link scheduling. Secondly, there is the timing difference of MAC offset parameter between TSCH and conventional IEEE802.15.4 Lastly, the devices in TSCH mode sleep during the time slots which are not assigned to itself.

• Journal of Digital Contents Society
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• v.13 no.3
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• pp.353-358
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• 2012

Wireless sensor networks consist of resource constraint devices which typically send data measured by sensors attached to the end devices towards a coordinator. The most often used medium access control protocol used in wireless sensor networks is the standard IEEE 802.15.4, where it is wireless standard introduced for low power, low cost wireless communication with moderate data rates. In this paper, we present implementation of both the IEEE 802.15.4 protocol stack and UART interface on the TI CC2530. We show that data via UART of our implemented IEEE 802.15.4 board are transmitted correctly in terms of captured frames.

• KIPS Transactions on Computer and Communication Systems
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• v.4 no.7
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• pp.235-238
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• 2015

IEEE 802.15.4 is the well-established standard enabling wireless connectivities among wireless sensor nodes. However, the wireless sensor networks based on IEEE 802.15.4 are inherently vulnerable to hidden nodes collision because the wireless sensor nodes have very limited communication range and battery life time. In this paper, we propose the advanced method of mitigating hidden nodes collision in IEEE 802.15.4 base wireless sensor networks by clustering sensor nodes according to channel quality information. Moreover, we deal with the problem of resource allocation for each cluster.

• Journal of Satellite, Information and Communications
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• v.5 no.2
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• pp.87-91
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• 2010

The IEEE 802.15.4 and IEEE 802.15.7 standard are the typical of low rate wireless and Visible Light Wireless personal area networks. Its Medium Access Control protocol can support the QoS traffic flows for real-time application through guaranteed time slots (GTS) in beacon mode. However, how to achieve a best allocation scheme is not solved clearly. The current analytical models of IEEE 802.15.4 MAC reported in the literature have been mainly developed under the assumption of saturated traffic or non-bursty unsaturated traffic conditions. These assumptions don't capture the characteristics of bursty multimedia traffic. In this paper, we propose a new analytical model for GTS allocation with burst Markov modulated ON-OFF arrival traffic.