基于IEEE 802.15.4 CSMA/CA机制的无线传感网络实时性能改进

Delay analysis for IEEE 802.15.4 scheme adopting a modified LIB model

自从IEEE802.15.4标准发布以来,低功耗、低速率传输的无线传感器网络的应用几乎涉及到现实生活的方方面面,而对这个标准的CSMA/CA机制实时性分析大部分都是基于BEB退避机制的分析。针对非饱和的CSMA/CA机制,提出了1种改进实时性能的退避机制LIB,采用马尔可夫链详细分析节点的访问过程和信道状态,并且基于这个模型,分析了不饱和、无ACK的IEEE 802.15.4信标使能访问机制的数据包传送时间,得到描述实时性能表达参数,包括数据包到达率、节点数量等参数对系统实时性的影响,从而定量改进实时性。本文的特点是采用线性增长而不是指数增长的退避机制,从而大大提高了数据包访问信道的时间性能;不饱和性是取决于数据包达到率而不是事先预定的idle长度。我们得到的分析结果与我们采用NS-2工具仿真的结果十分吻合。

Since the successful release of the IEEE 802.15.4 standard,advances in low-power and low-cost sensor networks have led to solutions mature enough to use in a broad range of applications.For time-critical applications,we use a modified Carrier Sense Multiple Access with Collision Avoidance（CSMA/CA） mechanism called Linear Increase Backoff（LIB） to enhance the performance of packet delay.An accurate and comprehensive Markov model is used to analyze packet delay of our LIB scheme,predicting it of unsaturated,unacknowledged IEEE 802.15.4 networks in which unsaturated states are dependent on the traffic condition rather than the depiction by a predetermined length.Simulation results are consistent with the predictions of this model.We also compare the performance of LIB with that of several mechanisms according to the optimal parameters selected from operating point,and find that packet delay is obviously superior to that of other schemes.