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

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 DCFbasic 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.

Newton-raphson method to solve systems of non-linear equations in VANET performance optimization

“…Generally, it seems that keeping CW size larger provide higher throughput especially in heavy load for lower priority traffics and also provide better fairness among priority classes in high loads and prevent from starvation in low priority traffics. However, to gain lower jitter in a heavy load for higher priority traffics, reducing CW size to smaller values acts better [8]. The probability that two nodes will try to access the medium at the same time is small, but when there are e.g.…”

Less-than-best-effort service for Community Wireless Networks: Challenges at three layers

“…However, certain parameters could be tuned -e.g. Request-to-Send/Clear-to-Send (RTS/CTS) could be enabled, reducing the chance for frame collision, a large Contention Window (CW) could be used [2] for transmitting LBE traffic to reduce the channel access probability for LBE user when subscriber's device has some data to transmit, or even complete sets of functions such as 802.11e (QoS) or Point Coordination Function (PCF) could be applied. PCF generally takes precedence over DCF, and could therefore be used to serve all but the LBE traffic.…”

Performance Evaluation of Ns2 and Omnet++ Simulators for Aodv Protocol in Manet

“…In OMNeT++ this parameter is defined as a constant of 255 in one of the source files. This size of contention window does have effect on traffic parameters like throughput in the network [11].…”