適用於IEEE 802.11 無線區域網路之碰撞感知式退避機制

In recent years, wireless local area networks (WLANs) are emerging as important instruments of wireless communications and network access. Several protocols have been proposed to manage multiple access to the shared wireless medium with the IEEE 802.11 being the most implemented protocol. The distributed coordination function (DCF) is the most widely deployed medium access control (MAC) protocol for IEEE 802.11 WLANs. The DCF is based on carrier sense multiple access with collision avoidance (CSMA/CA) scheme which employs the binary exponential backoff (BEB) algorithm. In the thesis, we propose an Improved Collision-Aware Backoff Mechanism (ICABM) which can dynamically select a suitable contention window size according to the contention level of current network and the history of the past trials. A contention level is separately estimated by each station depending on unsuccessful frame transmission ratios. Simulation results show that our scheme outperforms the standard protocol in terms of the average delay and system throughput.