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Enhanced distribution channel access — Modification of the intial & thereafter CW (EDCA-MITCW)

In recent years, IEEE 802.11 Wireless Local Area Networks (WLANs) have emerged as one of the prevailing technologies for the broadband wireless access. Although IEEE802.16 wireless network has become a newer generation of wireless network, it will be used as wireless metropolitan area network in the beginning because of its price. IEEE 802.11 network will continue to be the most important wireless local area network (WLAN) because of inexpensive price and easy installation. There are increasing number of applications found for WLAN which include real time traffic like Voice over IP and others. This causes more and more intensive research efforts on the quality of service (QoS) issues in “carrier sense multiple access/ collision avoidance (CSMA/CA)” for WLAN. Until now, the standard of IEEE 802.11e has stated some scenarios for this problem. In this paper, we focus on the adjustment of contention window of CSMA/CA after successful transmission of frame and the collision of multiple frames. In IEEE 802.11e, different contention window is given to different class of traffic. This will give higher priority to real traffic in a contention protocol. However, several researches have shown this method does not work very well in high load situation. For this, we propose a method to adjust the minimum contention window (CWmin) for different class of traffic according the number of stations and the collision rate of this class. Also, we propose a method to find the new contention window after collision. Simulation shows our protocol will have a good result under both light and heavy load situations.