• Proceedings of the Korea Information Processing Society Conference
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• 2014.11a
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• pp.199-202
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• 2014

본 논문은 IEEE 802.11 에서 QoS(Quality of Service)를 지원하는 환경에서 낮은 우선순위를 가지는 트래픽이 무선매체를 점유했을 때 TXOP 시간을 동적으로 적용하는 방법을 기술하였다. 본 논문에서는 IEEE 802.11e 환경에서 AP가 Beacon 메시지를 통하여 TXOP 시간을 통보함으로써 매체 접근 시도에 발생하는 충돌 감소와 낮은 우선순위 트래픽의 처리량을 증가하는 기법을 제안한다.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.4
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• pp.63-70
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• 2010

In IEEE 802.11e system providing differentiated services, there exist some problems as follows; collision probability increase due to the increase in the number of nodes by employing CSMA/CA transmission mode, transmission speed declining tendency towards the worst of it, which is caused by different transmission mode and decrease of TCP transmission rate as the result of the link occupancy by UDP when TCP shares the link with UDP by the TCP’s flow control characteristic. In this thesis, the initial minimum and maximum CW are set differently according to the number of connected nodes in the network to avoid collisions and TXOP is adjusted according to the channel state, in which ACs with low priority but better channel state will get gradually more chances to transmit leading to optimal channel capacity. Also, by allowing higher priority for ACK frames which control the TCP transmission, the flow control becomes better because that reduces the channel occupancy by UDP flow, and by this, fair transmission is obtained from the result of the more fair transmission and active resource allocation.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.11
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• pp.132-138
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• 2012

VANET(Vehicular Ad-hoc Network), standardization of IEEE 802.11p specification is in process. 802.11 MAC protocol grants all nodes equal opportunity to acquire channel without regard to their bit-rates, making it possible for lower bit-rate nodes to occupy communication channel for a fair amount of time thus keeping the higher bit-rate nodes from acquiring connection channel which downward-equalize the overall network performance. Also with the 802.11p MAC protocol, the probability of collision occurring increases as the number of nodes grow. The proposed algorithm is a new MAC protocol that guarantees nodes with acquired channel a firm priority over other nodes for a fixed amount of time with TXOP concept added to 'packet burst' according to the current transmitting speed. This newly designed algorithm allows the construction of wireless network with enhanced network throughput, decreased probability of collisions as well as providing the means to grant each node a fair chance of acquiring connection according to their channel conditions. The algorithm sets the CW's (Contention Window) width wider than the standard's and modulates the continuous transmitting threshold value depending on channel acquired time, thus improving the overall performance of the network.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9B
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• pp.775-785
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• 2008

We identify the problem of the current IEEE 802. lie HCCA (Hybrid Coordination Function Controlled Channel Access) scheduler and its numerous variations, that the queue information cannot be notified to the Hybrid Coordinator (HC) timely, therefore the uplink delay lengthens unnecessarily. We suggests a simple solution and a couple of implementation practices, namely the Adaptive Scheduler with RTS/CTS (ASR) and Adaptive Scheduler with Data/Ack (ASD). They are both further elaborated to emulate the Deficit Round Robin (DRB) scheduler. They are finally compared with existing exemplary schedulers through simulations, and shown to perform well.

• Proceedings of the Korean Information Science Society Conference
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• 2006.06d
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• pp.319-321
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• 2006

본 논문에서는 블록 FEC(Forward Error Correction) 알고리즘을 적용한 IEEE 802.11e MAC(Medium Access Control)의 블록전송모드(Block Transfer Mode)의 성능을 분석한다. 성능 향상을 위해서 IEEE 802.11e MAC은 TXOP(Transmission Opportunity)시간 동안 특정 스테이션(station)에게 독점적인 전송 기회를 부여하며, 이 기간동안 하나의 블록 즉 연속적으로 여러 개의 데이터 프레임(frame)을 전송한다. 수신자는 블록내의 각 프레임에 수신 여부를 블록 ack (block Acknowledgment)방식, 즉 하나의 ack 패킷이 모든 수신 프레임의 일련번호를 모아 알려 준다. 그러나 오류가 빈번한 무선 채널 환경에서는 블록 ack 방식을 사용하더라도 빈번한 재전송으로 인해 채널의 성능이 현저히 감소한다. 이러한 문제를 해결하기 위해 심볼 단위로 오류를 복원하는 블록 FEC 알고리즘을 적용할 수 있는데, 본 논문에서는 802.11e에서 FEC 알고리즘을 적응하는 두 가지 방식의 성능을 해석적으로 분석한다. 즉 두 가지 방식은 프레임 당 블록 FEC를 적용하는 방법과 전체 블록 내의 프레임을 하나의 데이터로 간주하여 FEC를 적용하는 방식이다. 본 논문에서는 이 들 두 가지 방식의 채널 성능 향상 정도와 블록 ack만을 사용한 경우의 성능을 수식적으로 계산한다. 실험에 의하면 BER이 $10^{-4}$인 채널 환경에서 블록 FEC를 적용한 방식이 블록 ack를 사용한 방식에 비해 약 1.5%의 성능향상을 보인다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.6
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• pp.1117-1119
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• 2015

In this letter, we propose a mathematical model of variable-length payloads transmitted in EDCA and transmitted using MU-MIMO. Assuming fixed-length or the use of mean value of payload length leads to discordant results while calculating the total payload length of variable-length frames transmitted within a fixed duration. Using the proposed model results in accurate results (less than 3% relative errors) for total payload length under variable-length traffic.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.11a
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• pp.1125-1128
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• 2005

최근 유비쿼터스 네트워크 환경을 구축하기 위해 많은 무선 통신 기술들이 등장하였다. 그 중 무선랜 기술은 쉬운 설치와 저렴한 비용 덕에 폭발적인 보급이 이루어 졌다. IEEE 802.11 표준을 기반으로 만들어진 무선랜은 여러 개의 전송속도를 지원한다. 대표적으로 802.11b 는 1, 2, 5.5, 11Mbps 의 4 가지 전송속도를 지원한다. 낮은 전송속도로 전송을 하면 패킷 전송시간은 증가하지만 비트 에러율은 감소된다. 각각의 전송속도에 따라 다른 패킷 전송 성공률을 갖게 된다. 한 무선랜 AP 에 연결된 노드들은 각자 자신의 처리율을 최대화할 수 있는 전송속도를 결정하여 사용하게 된다. 이러한 상황은 전체 시스템 성능에는 문제를 발생시킬 수 있다. 본 논문에서는 각자의 전송속도를 각자가 결정하는 것이 전체 시스템 성능에 문제를 발생시키는 경우를 보이고, 그것을 해결하기 위해 AP 가 각 노드의 전송속도 및 전송시간을 결정하는 기법을 제안한다. 나아가 무선랜에서의 문제점인 Performance Anomaly 현상을 해결하고, [3]에서 언급된 Inefficient Equilibria 현상도 막아본다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.1
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• pp.1-9
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• 2010

In this paper we propose a scheduling algorithm for supporting Quality of Service(QoS) in IEEE 802.11e HCCA referred to as ASR-DRR and ASD-DRR, which aims at providing improved performance for the support of multimedia traffic. Although We identify the problem of the current IEEE 802.11e HCCA (Hybrid Coordination Function Controlled Channel Access) scheduler and its numerous variations, that the queue information cannot be notified to the Hybrid Coordinator (HC) timely, therefore the uplink delay lengthens unnecessarily. We suggests a simple solution and a couple of implementation practices, namely the Adaptive Scheduler with RTS/CTS (ASR) and Adaptive Scheduler with Data/Ack (ASD). They are both further elaborated to emulate the Deficit Round Robin (DRR) scheduler. They are also compared with existing exemplary schedulers through simulation, and shown to perform well.