In order to improve the binary back-off algorithm of IEEE 802.11 DCF protocol,this paper proposes a dynamic sending-con-strained threshold-based back-off algorithm.According to contention degree of sites in networks on the use of channel resources the algorithm sets the dynamic threshold,and appropriately constrains the data sending of part sites.On the one hand,the algorithm does not modify the ad-justment mechanism of competition window of binary back-off algorithm but retains its advantages of simplicity and convenience in implementa-tion;on the other hand,it effectively solves the shortcomings of traditional binary back-off algorithm that it directly transmits data without in-specting the network status after the completion of back-off process and thus is prone to cause conflicts.Simulation results demonstrate that this algorithm can improve the saturation throughput and reduce the average access delay.%为了改进 IEEE 802．11 DCF 协议的二进制退避算法，提出一种基于动态约束发送门限退避算法。算法根据网络中站点对信道资源的争用程度设置动态门限，适当地约束部分站点数据的发送。一方面，算法没有对二进制退避算法的竞争窗口调整机制进行修改，保留了其简单、容易实现的优点；另一方面，有效地解决了传统二进制退避算法在完成退避过程后，没有考察网络状况而直接进行数据传输，容易产生冲突的缺点。仿真结果表明，该算法能够提高饱和吞吐量和降低分组平均接入时延。
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