CW Optimization for Low Density 802.11 Networks

Distributed coordination function (DCF) scheme is the basic mechanism of MAC layer in 802.11 standards. The element which controls the access to the channel is the value of Contention Window (CW). There is a process of this value management and the value of Contention Window is very important from the point of view of transmission Quality of Service parameters, especially the average throughput. Although CW has no direct influence on the current throughput value, if we take into account the average throughput in time unit, the situation is different. If high values of CW are drawn, as a result we obtain long backoff time (TBO) and the average throughput in normalized time unit will decrease since less time will be available for the data transfer. The throughput significantly depends on available transmission speed. However, this speed will be less critical if we have more time for the data transfer. In the paper, the authors analyze the influence of CWmin value on both collision rate and the TBO value. The CWmin decrease increases the collision rate and decreases the TBO value and the dead time simultaneously. Results of performed simulations show that for small Wi-Fi networks, the CWmin decrease can increase amount of time available for the data transmission.