This paper focuses on performance enhancement of the contention based access mechanism called Enhanced Distributed Channel Access (EDCA) introduced in the upcoming IEEE
802.11e standard. The use of transmission opportunity received little attention in previous QoS enhancement studies and contention window size was used as the main differentiation mechanism. Our approach, called Adaptive Transmission Opportunity (ATXOP), is derived from the EDCA. It aims to share the transmission channel efficiently and reduce the overhead cost. Relative priorities are provisioned by adjusting the transmission opportunity duration of each traffic class taking into account both applications requirements and medium utilization. We evaluate through simulations the performance of ATXOP scheme and compare it with the basic EDCA. The results show that our new approach outperforms the basic EDCA, especially at high traffic load conditions. Indeed, ATXOP increases efficiently the medium utilization ratio and so, it can provide an overall goodput up to 25% higher than EDCA while achieving delay differentiation.
