• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3A
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• pp.293-302
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• 2004

Wireless LAN is a rather mature communication technology that connects mobile terminals. A typical wireless LAN system is composed of one AP and more than one terminals, which is called a BSS. Terminals near to an AP can receive high rate data but terminals far from an AP may not receive data with guaranteed high speed rate because received signal strength is weakened. This paper proposes a method to allow high speed data transmission by grouping terminals and using part of wireless terminals as repeaters. We compare and analyze proposed grouping algorithms based on Depth First Search and Breadth First Search via simulations. A grouping algorithm based on Breadth First Search is shown to be more effective in term of efficiency and coverage.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10a
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• pp.299-301
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• 1998

화상회의 프로그램에서 회의 참여자간에 멀티 캐스팅을 이용하여 정보를 전송할 경우 point-to-point 방법보다 네트윅 트래픽을 상당히 줄일 수 있다는 장점이 있으나. 각 회긔 참여자간 모두 같은 QoS를 지원할 수밖에 없다는 단점이 발생한다. 본 논문에서는 전송할 자료를 몇 가지 그룹으로 나누어 그룹 전송함으로 다양한 QoS를 원하는 방법을 제시하고자한다.

• Information and Communications Magazine
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• v.30 no.11
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• pp.52-59
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• 2013

본고에서는 무선전력전송 국제표준 기술 동향과 산업 기술 동향에 대해 기술한다. 무선전력전송의 국제표준화는 ISO/IEC JTC1 SC6 그룹과 IEC TC100 TA15 그룹에서 진행 중이며, 산업 표준화는 WPC, A4WP, PMA를 중심으로 진행 중이다. 국제표준화기구에서는 인밴드 제어 프로토콜과 다수기기 및 다수 충전기 관리 프로토콜에 관한 국제표준화가 추진 중이고, 산업협의체에서는 제품 개발을 위해 송수신 시스템 및 제어 프로토콜에 관한 규격화를 추진 중이다. 향후, 산업표준 간의 호환성 유지를 위한 표준 개발이 절실히 필요하다.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.21 no.3
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• pp.75-88
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• 2011

Messages need to transmit to the neighbors securely in wireless sensor network, because a sensor node is deployed in hostile area. Thus it is necessary to support secure communication. One of the most important communication part is secure multicast. Especially, group rekeying is a big problem for multicast key management. So, group rekeying must be proceed securely when secrete information is exposed by attacker. Many group rekeying schemes have been studied for ad hoc networks. However, these schemes are Ill1desirable in WSNs. In this paper, we proposed a novel group rekeying scheme in WSNs that it has very powerful security.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.10
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• pp.1117-1130
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• 1992

In this study, we propose a protocol for the communication between process groups required during message transfers. This is accomplished by an efficient process management of distributed systems connected by computer networks. For a single process group, a multicast protocol was proposed, which can control message flows while maintaining the order of messages sent or delivered. Through use of membership-related services, a member composing a process group may leave and join the current a membership anytime during execution. Moreover, message delivery can be delayed by using a logical vector time stamp. The functionality of the message delivery includes a virtual synchronization in response to a change in membership.

• Journal of Internet Computing and Services
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• v.3 no.4
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• pp.11-18
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• 2002

The IP multicasting service system based on IGMP(Internet Group Management Protocol) is the receiver initiated multicasting system that all receivers must join to and leave from the server of multicasting service. The IGMP is less effective and reliable to apply the education system that all computers of students ore synchronized a teacher's computer. A proposed middle-ware in this paper provides the reliable data transferring and the server initiated multicasting system that client as student's PC is controled by a multicasting server as teacher's PC, This middle-ware is consisted with two major component, The one is the group manager that handle the status informations of members in each group. Another is the reliable sender/receiver that has The transmission protocol based on NAK message and flow control. As the results of the test that 22khz digital voice data and 1024$\times$768 24bit color image data were tested for 30 PCs connected with 100baseT, the voice data was completely without error transferred and the image data was successfully transferred with 0.004% retransmit rate under 2 frames/sec load.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2623-2631
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• 2010

In this paper, we propose a new interference cancellation(IC) receiver for multirate Multicarrier DS/CDMA(MC DS/CDMA) system based on orthogonal variable spreading factor(OVSF) code. The users are assigned different lengths of OVSF codes as a spreading code according to their data rates and the active users having same representative code split into a group for effective cancellation. The code grouping interference cancellation(IC) receiver performs cancellation between the groups first and cancellation within group. This proposed IC receiver can cancel the interferences using desired user's code information and then desired signals are detected. The results show that the large improvement in performance can be attained by group-wise IC scheme and we can make the effective systems compare to conventional ones. The bit error rate of the system is analytically derived in frequency selective Rayleigh fading channel and we also compare the system performance with that of multirate DS/CDMA system. We also analyze the performance of the proposed system with same bandwidth and processing gain. The results show the large improvement in performance that can be attained by cancellation scheme.

• Journal of the Korea Society of Computer and Information
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• v.14 no.5
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• pp.93-102
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• 2009

Environmental monitoring applications measure temporature, humidity, and pollution degrees of large areas periodically and are essential for ubiquitous society. In this paper, we propose a sensor network MAC protocol that is applicable to environmental monitoring applications. The proposing MAC protocol has scalability by constructing multiple groups of sensor nodes as in SMAC protocol. Differently from SMAC protocol, however, ours have hierarchical structure between adjacent groups. Data transmission schedules are efficient since lower groups are synchronized to higher groups. Thus. the end-to-end delays and energy consumption can be reduced due to sequential transmission schedules. But since the nodes within the same group are synchronized to themselves. they have good adaptability and scalability compared to existing hierarchical approaches such as DMAC. We show by simulations that the proposing MAC protocol is superior to SMAC for environmental monitoring applications.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.05a
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• pp.193-196
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• 2005

본 논문은 P2P 네트워크 환경에서 VOD 시스템의 새로운 프록시 캐싱 기법을 제안한다. P2P 환경에서 비디오 스트림을 그룹에 포함된 다수의 클라이언트에 저장하고, 이러한 클라이언트의 그룹을 Proxy로 활용하는 P2Proxy 기법을 제안한다. 우선 P2Proxy의 그룹에 포함된 클라이언트들과 서버간의 스트림이 전송되는 과정을 보였으며, 둘째 각 그룹의 생성과정과 서멸 과정에 대해 설명한다. 또한 클라이언트의 캐싱 정보를 공유하기 위한 디렉토리 구조를 기술하고 각 클라이언트의 참여 과정과 이탈과정을 보였다. 또 디렉토리 정보를 이용해 그룹에 참여한 다른 클라이언트의 정보를 계산하는 과정을 보였으며 이를 활용하여 재생과 전송 중에 메시지의 교환을 최소로 하도록 하였다. 제안된 P2Proxy 기법은 기존의 P2VoD 기법에 비하여 서버에 대한 부하의 요구량이 훨씬 작은 결과를 보였다.

• Proceedings of the Korean Information Science Society Conference
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• 2007.10d
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• pp.1-6
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• 2007

프락시 암호 기법은 안전한 그룹 통신에서 중간 노드 신뢰 문제를 해결하기 위한 좋은 방법을 제공한다. 기존의 연구에서 프락시 암호 기법을 이용한 방법들이 제안되었으나 이들은 멀티캐스트 데이터전송 측면에서 매우 비효율적이거나 1-affect-n 문제로 인해 확장성이 저하되는 단점을 가지고 있다. 이에 따라 이 논문에서는 그룹 가입/탈퇴 분석 모델에 기반하여 동적으로 그룹을 분할/병합함으로써 키 분배에서의 확장성과 데이터 전송에서 효율성을 같이 제공하는 새로운 프락시 암호 기반의 안전한 그룹 통신 기법을 제안한다. 제안한 방법은 인터넷이나 무선 네트워크와 같이 공개된 환경에서 가입/탈퇴가 빈번히 일어나는 대규모 가입자를 대상으로 하는 실시간 멀티미디어 방송 서비스에 적합하다.