WiFi technology is undoubtedly the most popular technology amongst today’s WLAN technologies; in a way that these days we can find few places in which this technology has not been adopted. The main reason for this popularity should be found in 802.11 standard and particularly in its MAC layer which is the foundation for emerging this technology. 802.11 provides a simple mechanism, yet with an acceptable performance for most general uses, in order to access the wireless medium. This simplicity in turn causes easier implementation, lower cost and possibility of quick establishment of the WLAN. The primary version of this standard published in 1997, was mainly designed and implemented to provide best-effort services. Years later, with increasing the willingness to use applications like VoIP and video-conferencing in the public level, the need for differentiating services revealed itself. As a result in 2005, 802.11e with the purpose of providing QoS according to requestedlevel of the applications was published. The main protocol for the MAC layer of this version is called EDCA which can be considered as evolved DCF in previous versions. Nevertheless, in recent years as kinds and amounts of QoS demanding applications have grown fast and continues growing and also the willingness to use these networks for industrial applications in order to provide soft QoS requirements, have encouraged researchers to improve the performance of 802.11e-EDCA. Towards this approach, current thesis proposesa solution inwhichwhile it preserves the framework of the protocol and being committed to its principles, it can providea better performance for higher priority messages from the aspect of QoS parameters, as the number of the nodes increases. The proposed solution first investigates possible preventing causes in the MAC layer level for achieving the desired QoS and thenconsidering these causes, proposes appropriate mechanism. In this solution, the TDMA mechanism is extended in a way that in the first place, it could be implemented within the principles of EDCA and at the next step to decrease the effects of its weakness points like its sensitivity to the variance of the number of users in the network. Keywords: Qos, MAC layer, WiFi technology, 802.11 standard, EDCA
