利用訊號變化與遮蔽效應之802.11 MAC碰撞避免協定

IEEE 802.11 DCF is widely used and able to avoid the collisions of the hidden terminal problem in a wireless network. However, there may be collisions existing in the DCF MAC protocol. That is, when a node in NAV state does not receive any control signal, a collision may occur after the node ends the NAV period. In this paper, to solve this collision problem, a detailed analysis about the problem is given. Afterwards, according to the analysis, we utilize the “masking effect” and the detection of signal variation to design the MAC collision avoidance protocol. With the received signal strength and the variation of received signal strength of a node, the node can determine whether there are other transmissions occurring in the transmission range. Therefore, a node can determine whether the period of NAV state can be extended to avoid collisions. Simulation results show that our proposed MAC protocol can efficiently reduce 60% and 41% collisions than the IEEE 802.11 DCF protocol and OCS-MD. In addition, our proposed MAC protocol also shows shorter transmission delay and lower retransmissions than the 802.11 DCF and OCS-MD to have better network throughput.