• Journal of Korea Multimedia Society
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• v.12 no.12
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• pp.1769-1777
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• 2009

With the advent of the ubiquitous technology age, the progress of network technology has enabled a robust sensor communication, not just in cities, but also in poor surroundings such as deserts, polar regions, or underwater environments. In this paper, we propose a Multiple Acknowledgement (MA) technique to replace the conventional Automatic Repeat request (ARQ) technique. The MA mechanism is to send an Ack to many receivers simultaneously. The CH (master, coordinator) of the unit cluster broadcasts a Beacon frame where Ack information of the previously transmitted data is included. This technique can reduce the number of transmissions and overhead significantly. The proposed technique is a scheme improving the efficiency of an underwater sensor network where the uplink data transmission is the mainstream. The Performance of the ARQ, Block Ack, Pervasive Block Ack and the proposed method were compared with one another and analyzed. The proposed method showed significant performance improvement as compared with the ARQ, BA, and PBA in its channel efficiency.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.05a
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• pp.841-844
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• 2008

본 논문은 공개 네트워크 시뮬레이터 ns-2.31(Network Simulator 2.31)의 802.11 DCF 모듈에서 버그(bug)를 소개하고 이의 영향 결과를 분석한다. ns의 802.11 DCF 모듈은 다음과 같은 문제점을 가지고 있다. 첫째, 백오프(backoff) 알고리즘은 표준안에서 명시한 알고리즘대로 작성되지 않았다. 둘째, 특정조건에 해당되는 충돌에 대하여 트레이스 파일에 출력하지 않는다. 셋째, 전파 오류 모듈을 삽입하여도 전파 오류 결과를 트레이스 파일에 출력하지 않는다. 넷째, MAC(Medium Access Control) 알고리즘만을 평가할 수 있는 기법을 제공하지 않는다. 이러한 문제점을 수정한 ns-2와 수정전의 ns-2와 평균4.6%의 충돌률 차이를 보인다.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.05a
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• pp.907-910
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• 2007

본 논문에서는 Ad-hoc 네트워크에서 패킷 flooding에 의해 발생하게 되는 broadcast storm problem [1]을 해결하기 위한 크로스 레이어 기반의 flooding 기법을 제안한다. 제안된 flooding 기법은 크로스 레이어 프로토콜을 기반으로 하여 물리계층과 MAC (Medium Access Control) 계층에서 이웃 노드들에 대한 정보를 수집하고, 이를 이용하여 효율적인 재전송 노드의 수를 결정한다. 모의 실험을 통한 성능평가에서는 전체 네트워크 노드에 대한 수신 비율이 simple flooding 에 근접하며, 전송 비율 및 평균중복패킷 수에서도 좋은 성능을 보임으로서 broadcast storm problem을 해결할 수 있다.

• Journal of the Institute of Convergence Signal Processing
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• v.9 no.1
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• pp.39-45
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• 2008

This paper considers the multi-objective optimization of a multi-service arrayed waveguide grating-based single-hop WDM network with the two conflicting objectives of maximizing throughput while minimizing delay. This paper presents a genetic algorithm based methodology for finding the optimal throughput-delay tradeoff curve, the so-called Pareto-optimal frontier. Genetic algorithm based methodology provides the network architecture parameters and the Medium Access Control protocol parameters that achieve the Pareto-optima in a computationally efficient manner. The numerical results obtained with this methodology provide the Pareto-optimal network planning and operation solution for a wide range of traffic scenarios. The presented methodology is applicable to other networks with a similar throughput-delay tradeoff.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6B
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• pp.338-348
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• 2005

Currently, IEEE 802.11 Wireless LAN (WLAN) is rising as the most popular means for the broadband wireless access network. In this thesis, we propose a QoS(Quality of Service)-Oriented mechanism using handshaking method of scanning phase in IEEE 802.11 handoff. In conventional process for handoff, the major criterion to select the best AP(Access Point) among candidates is normally based on the RSS(Received Signal Strength), which does not always make the selected network guarantee the maximum achievable performance. Even though the link quality with a neighboring AP is excellent, the AP may not be a good candidate to handoff to simply because MAC(Medium Access Control) protocol of IEEE 802.11 standard is contention-based such as CSMA/CA. Therefore, if we apply network level information to AP selection criteria, we can achieve better handoff efficiency rather than before. The analysis and simulation results applied to our new mechanism show clearly better performance than AP selection based on traditional handoff method.

• Journal of IKEEE
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• v.2 no.1 s.2
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• pp.114-121
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• 1998

This paper proposed a collision avoidance scheme to improve the network performance and priority control scheme to support real-time ATM applications in CIF(Cells in Frames), which carries ATM cells over existing Ethernet interfaces. The proposed scheme has optimized for the two nodes Ethernet, that is a typical CIF network, and doesn't require any hardware modification of existing Ethernet interface card. The collision avoidance scheme gives fair access opprtunities with minimized contention to the nodes by assigning different inter-frame gap to each element of CIF network. The priority control scheme guarantees preemptive transmission of real-time frames to the medium by exchanging queuing status information between two nodes. Therefore in this paper it is shown that CIF network which has both the collision avoidance scheme of MAC layer and the priority control scheme of CIF layer has a improved network performance and supports real-time ATM applications efficiently.

• The KIPS Transactions:PartC
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• v.12C no.5 s.101
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• pp.679-686
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• 2005

Because EPON access network shares a medium and aggregates the traffic from EPON subscribers, scheduling media access control on EPON bandwidth allocation is very important. Furthermore DBA mechanism of EPON based on TDMA is out of specification and up to implementation. This paper deals with a DBA method to guarantee the QoS of the delay sensitive traffic on the base of best-effort service and delay priority queue management. The proposed method performs virtual scheduling algorithm for the integrated traffic. It uses the same MAC messages and tries to guarantee the QoS of higher priority traffic first with a simple DBA architecture. We evaluate the algorithm for traffic delay according to polling interval and traffic load of upstream and downstream. The results show that the proposed method can guarantee the QoS of the delay sensitive traffic with priority of the service classes.

• Journal of Advanced Navigation Technology
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• v.15 no.5
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• pp.764-773
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• 2011

IEEE 802.15.4 is a standard for LWPAN based on TDMA. IEEE 802.15.4 has not been used widely because of restrictions on the QoS, scalability, and reliability. IEEE 802.15.4 utilizes GTS for one-hop QoS transmission. However GTS is not an effective method to satisfy QoS in multi-hop environments. Currently IEEE 802.15.4e, an extended version of IEEE 802.15.4 MAC sub-layer, is being developed to satisfy more diverse performance requirements than IEEE 802.15.4. IEEE 802.15.4e provides muti-hop QoS transmission functionality and uses multiple frequency channels. In this paper, a multi-channel TDMA scheduling scheme is proposed to satisfy end-to-end transmission delay in IEEE 802.15.4e. The performance of the proposed scheme is evaluated using simulation.

• Journal of Advanced Navigation Technology
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• v.11 no.1
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• pp.24-30
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• 2007

The integration of WLAN and beyond 3G mobile networks offers the possibility of achieving anytime and anywhere Internet access. Moreover the requests for seamless multimedia services and the Quality of Service (QoS) support have been one of key issues in wireless networks. Therefore the researches relative to seamless multimedia service and QoS over heterogeneous wireless networks have been progressing rapidly. In this paper, we propose inter-working architecture for supporting seamless multimedia service and QoS over WLAN and WiBro networks. Based on the proposed inter-working architecture, we also provide both the seamless handover architecture such an inter-network vertical handover and the QoS-aware wireless Medium Access Control (MAC) scheme. In addition, we evaluate and compare the performance by Network Simulator-2 (NS-2) simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6B
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• pp.595-604
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• 2009

The HCCA reserves the channel resources based on the mean data rate in IEEE 802.11e. It may cause either the waste of channel resource or the increase of transmission delay at MAC layer if the frame size is rapidly varied when a compressed mode video codec such as MPEG video is used. To solve these problems, it is developed that the packet scheduler allocates the wireless resource adaptation by according to the packet size. However, it is difficult to perform the admission control because of the difficulty with calculating the available resources. In this paper, we propose a CAC mechanism to solve the problem that may not satisfy the QoS by increasing traffic load in case of using EDCA. Especially, the proposed CAC mechanism calculates the EB of TSs using the traffic information transmitted by the application layer and the number of average transmission according to the wireless channel environment, and then determines the admission of the TS based on the EB. According to the simulation results of the proposed CAC mechanism, it admitted the TSs under the loads which are satisfied within the delay bound. Therefore, the proposed mechanism guarantees QoS of streaming services effectively.