Article

Wireless Personal Communications

, Volume 43, Issue 4, pp 1267-1278

First online:

Effect of the contention window size on performance and fairness of the IEEE 802.11 standard

  • Azade KhalajAffiliated withECE Department, University of Tehran
  • , Nasser YazdaniAffiliated withECE Department, University of Tehran Email author 
  • , Maseud RahgozarAffiliated withSchool of Electrical and Computer Engineering, Control and Intelligent Processing Center of Excellence, University of Tehran

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Abstract

IEEE 802.11 is a widely used standard for MAC and PHY layers of WLANs. Unfortunately, the access methods offered in this standard cannot support QoS (Quality of Service) for real-time traffics. Using multimedia applications over WLANs is increasing and, on the other hand, it seems that the access methods employed in this standard causes high variations in delay or jitter and wastes bandwidth due to collisions. There are many methods to enable DCF—basic access method in 802.11—with service differentiation and QoS. The difficulty in majority of these methods is unfair bandwidth allocation among low and high priority traffics at high loads resulting starvation for low priority traffics. In this paper, we modify the way that the CW (Contention Window) size is calculated after a successful transmission and study the effect of the CW size on performance and fairness. Results of our simulations show that the performance of DCF with this modification is better, specially, for traffics in which throughput is the most important parameter. Besides, this method provides better fairness among low and high priority traffics. We also employ a scheme to enable 802.11 with service differentiation which grants dynamic priority to low priority traffics to prevent starvation, specially, in high loads.

Keywords

Wireless Communications 802.11 MAC Quality of Service (Qos) Fairness