基于全网冲突的自适应退避算法的研究

摘要

退避算法的设计对基于竞争的IEEE 802.11协议影响重大,而退避的前提取决于冲突的发生和正确判断.在DCF协议的基础上提出了一种基于全网冲突的自适应调整竞争窗口的新型退避算法(CWN-BEB).CWN-BEB算法通过统计全网冲突次数(即整个网络所有节点发生冲突的总次数),使全网冲突对节点透明,并引入一个新的变量全网冲突概率来自适应改变竞争窗口大小.此算法未引入额外开销,可以很好地与IEEE802.11 DCF协议兼容,实现复杂度低.仿真结果表明,在低负载情况下,CWN-BEB算法可以较好地向DCF协议收敛;在高负载情况下,CWN-BEB的时延和吞吐量等性能明显优于IEEE 802.11 DCF协议.%The design of backoff algorithm has an important impact on IEEE 802.11 protocol utilizing distributed coordination function (DCF) as the commercial WLAN MAC access mechanism,and the precondition of back-off lies on whether the collision happened and distinguished correctly.This paper proposed a new binary exponential back-off algorithm which was based on collisions of the whole network (CWN-BEB).CWN-BEB added up all the collisions happened in the network and made it known to all the nodes,and then introduced a new variable (whole network probability) to self-adaptively change the value of contention window based on the collisions in the network.CWN-BEB could be easily implemented without any additional overheads and it was backward compatible with IEEE 802.11 DCF protocol.Finally,the simulation results demonstrate that when in low-duty situations,the performances of delay and throughput of CWN-BEB can well converge to IEEE 802.11 DCF protocol.in heavy-duty situations,the performances of delay and throughput of CWN-BEB are better than that of IEEE 802.11 DCF protocol.