Quality of Service in IEEE 802.11 WLANs


The proposed IEEE 802.11e draft standard defines new MAC protocols for QoS in wireless networks, mainly HCF and EDCF. EDCF is a contention-based channel access scheme and is part of HCF for infrastructure networks and may be used as a separate coordination function for wireless ad-hoc networks. Throughout the project, we have proposed to extend EDCF with a dynamic adaptation algorithm of the minimum contention window (CWmin) that enables each station to tune the size of the CWmin (the same approach is also applied for CWmax) used in its back-off algorithm at run time. The purpose of our scheme is to reduce delay and jitter and increase the efficiency of the transmission channel. Priorities between access categories are provisioned by tuning the size of the CWmin according to application requirements and channel conditions. The performances of the IEEE 802.11e EDCF, enhanced with our adaptation algorithm, are extensively investigated by simulations and compared with contention window adaptation schemes especially Slow Decrease (SD) schemes. Results obtained indicate that CWmin adaptation scheme outperforms the 802.11e EDCF standard in terms of channel utilization, throughput, and packet delay. More details about obtained results can be found in project reports research reports

Report – Results

  • L. Gannoune, S. Robert and D. Rodellar. A Survey of QoS Techniques and Enhancements for IEEE 802.11 Wireless LANs. EIVD-Swisscom Inno. report- May 2003
  • ns-2 Simulation code and Results: CWmin.tar.bz2: Dynamic tuning of CWmin, CWmax.tar.bz2: Dynamic adaptation of CWmax and ns-edcf code