A Virtual Collision Solution Scheme Based on Optimal Window for WLAN

IEEE 802.11 DCF exhibits poor performance as the number of nodes increases in a wireless LAN due to high collision probability on each transmission. In this paper, based on the optimal constant backoff (OCB) window scheme which fixes the backoff window at every backoff stage, a virtual collision solution (VCS) scheme is proposed to reduce the collision probability and to enhance the throughput performance. In our scheme, if more than one nodepsilas backoff timer reaches zero, they should enter a virtual collision phase containing several contention cycles. In each contention cycle, every competing node transmits a burst to jam the channel and a node senses the medium busy will retire from the contention. Moreover, an analytical model is proposed which shows the high efficiency of elimination in VCS with negligible cost. Both analysis and simulation results show that our proposed scheme achieves higher throughput and lowers the collision probability compared to the DCF and OCB.