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Journal of Information Science and Engineering, Vol. 23 No. 6, pp. 1707-1721 (November 2007)

Enhanced Fair Scheduling for IEEE 802.11e Wireless LANs*

Kun-Nan Tseng, Kuochen Wang+ and Hung-Cheng Shih
Department of Computer Science
National Chiao Tung University
Hsinchu, 300 Taiwan
*E-mail: kwang@cs.nctu.edu.tw

As wireless LANs are gaining popularity, the demand for supporting multimedia and QoS-sensitive applications becomes more important than before. Although enhancements to the legacy IEEE 802.11 MAC to support QoS mechanisms have been proposed, they suffer from unfair allocation of bandwidth between high and low priority traffic. We propose a distributed enhanced fair scheduling (EFS) scheme that can conquer the above problem. With a fast backoff mechanism in the backoff timer decrement state and by dynamically adjusting backoff intervals according to the network load, we can enhance the performance of the EFS. We have evaluated the performance of the EFS through simulation. Experimental results show that the proposed EFS has better throughput performance than DFS by 13%, lower average MAC delay than DFS by 6% and the two have nearly equal fairness. Although the enhanced distributed channel access (EDCA) in IEEE 802.11e has better throughput and delay performance than EFS and DFS, it has very poor fairness. The contention free burst (CFB) mechanism in EDCA is the main factor that results in good throughput performance, lower average MAC delay and poor fairness. Our EFS is very suitable for applications that need strict fair bandwidth allocation, such as pay services.

Keywords: backoff interval, fair scheduling, IEEE 802.11e, quality of service, wireless LAN

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Received September 6, 2005; accepted February 6, 2006.
Communicated by Yu-Chee Tseng.
*This work was supported by the NCTU EECS-MediaTek Research Center under grant Q583 and National Science Council under grant NSC93-2213-E-009-124. A brief version of this paper was presented at the 11th Mobile Computing Workshop, Taoyuan, Taiwan, March 2005: Sponsor V National Science Council (NSC).