IEEE 802.15.4 MAC协议退避机制的改进

考虑节点移动且数据传输率不断变化对网络性能的影响，针对IEEE802.15.4提出了一种网络负荷概率判断和指数加权滑动平均(PJNL_EWMA) 的退避策略，在每次载波监听多路访问/冲突避免（CSMA/CA）算法开始时采用网络负荷概率判断思想判定当前网络状况，然后通过指数加权滑动平均方法动态地调整退避指数。通过NS2的仿真结果表明：与IEEE802.15.4标准协议算法及MBS+EWMA算法相比，PJNL_EWMA算法不仅提高了网络吞吐量，同时还减小了数据包的丢包率和碰撞概率，提高了网络性能。

Improved backoff mechanism for IEEE 802.15.4 MAC protocol

Concerning the impact on network performance of the mobile nodes and the constantly changing data transmission rate, the authors proposed a new backoff scheme for IEEE802.15.4, which used Probability Judgment based on Network Load and Exponentially Weighted Moving Average (PJNL_EWMA) method. According to a real time monitoring of current network status by probability judgment of network load, this method dynamically adjusted backoff exponent by EWMA when Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) began. Compared with the IEEE802.15.4 standard protocol and MBS (Memorized Backoff Scheme)+EWMA algorithm, the simulation experiments on NS2 platform show that the PJNL_EWMA algorithm not only improves the throughput of the network, but also reduces the packet loss rate and the collision ratio, significantly improving the network performance.