Capture effect on the optimal contention window in IEEE 802.11 based WLANs

Wireless local area networks (WLANs) adopted IEEE 802.11 based carrier sense multiple access with collision avoidance (CSMA/CA) multiple access control (MAC) protocol. Throughput in a WLAN significantly depends on the minimum contention window (CW) parameter of CSMA/CA MAC protocol. Without considering the capture effect, i.e., by using a protocol model, G. Bianchi models the optimal value of the minimum CW of a WLAN as N√2T_c, where N is the number of contending nodes in the WLAN and T_c is the collision time in mini-slots [1]. In this paper, we study the capture effect on the throughput and the optimal value of minimum CW in WLANs. By extensive simulation study, we show that the throughput performance improves in a WLAN due to the capture effect. However, the improvement due to the capture effect reduces with increasing the minimum CW of the nodes and it is negligible at the optimal value of the minimum CW. We also investigate that the optimal value of the minimum CW under the capture effect is close to the optimal value of the minimum CW given by Bianchi model. In WLANs, very close to the optimal throughput can be obtained by configuring the minimum CW with the simple Bianchi model even when a realistic physical interference model, i.e., the capture effect is considered.