• Journal of Korea Multimedia Society
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• v.12 no.8
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• pp.1109-1119
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• 2009

WLAN(Wireless Local Area Network) standard is currently developing with increased wireless internet demand. Though existing IEEE 802.11e demonstrates that data rates exceed 54Mbps with assuring QoS(Quality of Service), wireless internet users can't be satisfied with real communication system. After IEEE 802.11e system, Study trends of IEEE 802.11n show two aspects, enhanced system throughput using aggregation among packets in MAC (Medium Access Control) layer, and better data rates adapting MIMO(Multiple-Input Multiple-Output) in PHY(Physical) layer. But, no one demonstrates IEEE 802.11n system performance results considering MAC and PHY connection. Therefore, this paper adapts MIMO in PHY layer for IEEE 802.11n system based on A-MPDU(Aggregation-MAC Protocol Data Unit) method in MAC layer considering MAC and PHY connection. SVD(Singular Value Decomposition) method with WLAN MIMO TGn Channel is used to analyze MIMO. Consequently, Simulation results show enhanced throughput and data rates compared to existing system. Also, We use Ns-2(Network Simulator-2) considering MAC and PHY connection for reality.

• 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 Korean Institute of Communications and Information Sciences
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• v.33 no.4B
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• pp.192-198
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• 2008

In this paper, we propose a scheme that improves the transmission performance of realtime multimedia data in wireless Local Area Network (LAN) environment, through the dynamical control of Transmission Opportunity (TXOP) period of the IEEE 802.11e HCCA Medium Access Control (MAC). The existing schedulers which determine the frame transmission time and its duration could not appropriately cope with the change of physical transmission rate, since the TXOP period has remained unchanged with the change of transmission rate of the wireless station. Our scheme is devised to keep the transmission performance of real-time multimedia data effectively unchanged by making TXOP period be extended when the transmission rate gets reduced. The proposed scheme is experimented along with IEEE 802.11e reference model using NCTUns simulator, which shows that the multimedia data is effectively delivered with the change of transmission rate as the distance between the wireless station and its access point increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.8A
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• pp.820-827
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• 2010

In these days, video applications for special purposes such as video conference systems among multiple users and video surveillance systems require multiple video connections and QoS guarantee. The video systems employ IEEE 802.11 Wireless LAN devices to support broadband wireless interfaces and easy internet accesses for cheaper prices. However, according to the current IEEE 802.11e HCCA standard, if more than three video sessions are established in WSTA services, some of them must share the TXOP because the available number of TSIDs for video transmission is two. In order to resolve the problem, we devised a method which can establish up to 15 video sessions by slightly modifying the frame structure while maintaining the compatibility with current standard. Our method is implemented on the NCTUns 4.0 network simulator, and evaluated not only numerically in terms of throughput, delay, and PSNR, but also experimentally in the sense of real video clips that are used as input to our simulation. The results showed that our method sufficiently guarantees the transmission bandwidth requested by each video session.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.99-109
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• 2007

IEEE 802.lie is being proposed to improve QoS by IEEE 802.11 working group. HCCA (HCF Controlled Channel Access) a centralized polling based mechanism of IEEE 802.11e, needs a scheduling algorithm that decides on how the available radio resources are allocated to the polled STAs. In IEEE 802.l1e standard Reference Scheduler is presented. Reference Scheduler Polls all STAs in a polling list by the same interval that causes ineffectively frequent polling. It increases not only the overhead but it decreases the TXOP (Transmission Opportunity) utilization. In this paper, we propose the scheduling and admission control algorithm that poll stations depending on the MSI (Maximum Service Interval)o( stations to solve these shortcomings. In our proposed algorithm a station is polled by an interval close to its MSI, so polling overhead decrease and TXOP utilization increases than Reference Scheduler. Simulation results show that our algorithm outperforms Reference Scheduler. Our algorithm maintains higher aggregate throughput and services mere stations than Reference Scheduler.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.245-248
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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 as 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. Current IEEE 802.11e, however, is not sufficient to support service differentiations and network performance enhancements, under a varying network environment experiencing as varying channel characteristics and high network loads. Recently, there have been much research to complement this deficiency of 802.11e standard. This paper surveys these research efforts.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.21-22
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• 2007

The reference scheduler presented by IEEE 802.11e standard is inefficient because it polls all admitted stations in the same interval. It increases poll overheads and waste time. In this paper we proposed an efficient scheduling algorithm to improve the aggregate throughput and the number of admitted stations.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06a
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• pp.373-376
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• 2011

무선 멀티 홉 네트워크는 채널 상태의 불안정으로 인해 전송 지연, 패킷 손실 등의 발생이 빈번하며 홉 수가 증가할수록 이와 같은 품질 저하는 더욱 심각해진다. 무선 멀티 홉 네트워크에서 QoS를 보장하기 위해 IEEE 802.11e에서는 우선순위가 높은 노드에게 정해진 시간 동안 연속해서 보낼 수 있도록 TXOP(Transmission Opportunity) 파라미터 값을 정해놓고 있다. 하지만 IEEE 802.11e는 단일 홉 네트워크를 가정하여 설계되었기 때문에 멀티 홉 무선 환경에서 홉 수의 증가에 따른 지연 및 손실 증가를 고려하지 않는다. 본 논문에서는 멀티 홉 환경에서의 QoS 지원을 위한 DTA (Dynamic TXOP Allocation) 메커니즘을 제안하였다. DTA 메커니즘은 네트워크 상황을 고려한 동적 TXOP 할당 기법으로, 각 노드의 전송 큐 상태와 종단간 전송 지연 비율을 판별하여 이에 따른 QoS 지원을 위한 동적 TXOP를 할당한다. 이를 통해 불안정한 채널 상태 및 멀티 홉 환경에서 홉 수 증가에 따른 성능 감소를 개선할 수 있었다.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.34-39
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• 2006

IEEE 802.11e 무선LAN 매체접근제어(MAC) 통신규약의 분산조정함수(DCF)의 성능은 경쟁노드수가 증가할수록 급격히 떨어진다. 이러한 문제점을 해결하기 위해서 채널의 유휴슬롯시간(Idle Time)을 측정해서 최소 경쟁윈도($CW_{min}$)를 조절하는 방식이 제시되었다. 이러한 방식을 각 부류별로 서비스 품질이 보장되는 IEEE 802.11e 네트워크로 확장하여 성능을 최대화하는 기법을 이 논문에서 다루겠다. 각 부류별로 서비스품질은 유지하면서 네트워크 전체의 성능을 높일 수 있는 최적의 경쟁윈도 크기를 찾아내는 기법을 보이도록 하겠다.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.1045-1046
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• 2006

The IEEE 802.11e medium access control (MAC) is an emerging standard to support Quality of Service (QoS). A HCCA (HCF controlled channel access) scheduler of the standard IEEE 802.11e is only efficient for flows with strict constant bit rate (CBR) characteristics. In this paper, we propose a new HCCA scheduling scheme that aims to be efficient for both CBR and VBR flows. The proposed scheme uses fuzzy queue length predictions to tune its time allocation to stations. We present a set of simulations and provide performance comparisons with the reference HCCA scheduler.