• Proceedings of the Korea Contents Association Conference
• /
• 2007.11a
• /
• pp.611-614
• /
• 2007

The IEEE 802.11 Task Group E has worked to enhance the legacy 802.11 MAC to expand support for applications with QoS requirements. EDCF(Enhanced Distributed Coordination Function) of IEEE 802.11e is enhanced from DCF(Distributed Coordination Function) of 802.11 and It has differential AC(Access Category). In this paper, we change parameters(AIFS, CWmax) and make an analysis of network performance. We use NS-2 to verify change of network performance.

• Proceedings of the Korean Society of Computer Information Conference
• /
• 2009.01a
• /
• pp.289-292
• /
• 2009

IEEE 802.11 WLAN(Wireless LAN)은 효율성과 편리함으로 시장에 급격히 보급되었다. 이 IEEE 802.11 WLAN은 CSMA/CA를 기반으로 하는 DCF방식을 주로 사용하고 있으며, Contention Window, Backoff Size를 이용한 각 단말기들간의 자유 경쟁에 의한 전송 방식을 택하고 있다. 그 주된 방법으로 단말기는 CW를 설정하고 CW범위안에서 랜덤한 값을 정해 Backoff Counter를 줄여 채널을 점유하는 방식이다. DCF방식은 채널을 두고 여러 대의 단말기가 서로 경쟁을 함으로써 채널을 할당 받아 사용하게 된다. 본 논문에서는 이러한 채널 할당시 CW값을 조절하여 다른 단말기보다 채널을 빨리 할당받고 높은 처리량을 나타내는 탐욕적(Greedy) 노드문제에 대해서 분석하는 방법에 대해서 설명하려고 한다.

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.47 no.6
• /
• pp.28-39
• /
• 2010

The study aims at offering a solution to the problems of transmission delay and data throughput decrease as the number of contending On-Board Units (OBU) increases by applying CSMA medium access control protocol based upon IEEE 802.11p. In a competition-based medium, contention probability becomes high as OBU increases. In order to improve the performance of this medium access layer, the author proposes EDCA which a adaptive adjustment of the Contention Windows (CW) considering traffic density and data type. EDCA applies fixed values of Minimum Contention Window (CWmin) and Maximum Contention Window (CWmax) for each of four kinds of Access Categories (AC) for channel-specific service differentiation. EDCA does not guarantee the channel-specific features and network state whereas it guarantees inter-AC differentiation by classifying into traffic features. Thus it is not possible to actively respond to a contention caused by network congestion occurring in a short moment in channel. As a solution, CWminAS(CWmin Adaptation Scheme) and ACATICT(Adaptive Contention window Adjustment Technique based on Individual Class Traffic) are proposed as active CW control techniques. In previous researches, the contention probabilities for each value of AC were not examined or a single channel based AC value was considered. And the channel-specific demands of IEEE 802.11p and the corresponding contention probabilities were not reflected in the studies. The study considers the collision number of a previous service section and the current network congestion proposes a dynamic control technique ACCW(Adaptive Control of Contention windows in considering the WAVE situation) for CW of the next channel.

• Journal of KIISE:Computing Practices and Letters
• /
• v.14 no.2
• /
• pp.191-195
• /
• 2008

This paper proposes a technique for improving IEEE 802.11e EDCA's performance by dynamically adjusting each class's contention window size based on each class's traffic amount. For providing differentiated service differently from 802.11, 802.11e EDCA maintains four classes each of which specifies different static minimum and maximum contention window sizes. Since the initial window sites significantly affect the 802.11e performance, several window adjustment schemes have been proposed. One of the schemes known as CWminAS (CWmin Adaptation Scheme) dynamically and synchronously determines the four windows' site based on the periodically measured collision rate. This method, however, can lower the send probability of high priority classes since it can't differentiate their collisions from those of low priority classes, leading to the channel underutilization. For solving this problem, we propose ACATICT(Adaptive Contention-window Adjustment Technique based on Individual Class Traffic) algorithm which adapts each class window size based on each individual collision rate rather than one average collision rate. Our simulation experiments show that ACATICT achieves better utilization by around 10% at maximum.