中文摘要：

在传统的追踪系统中，移动节点需要周期性地向服务器汇报其位置信息。但是随着移动节点数目的增加，这种方式会导致很高的丢包率和快速的能量消耗。同时，在实际的追踪应用中，观察到节点之间距离通常很接近。因此，如果选出部分节点作为代理，由代理节点周期性地汇报位置信息能够极大地减少网络中的消息复杂度和能量消耗。基于此想法，提出了无线传感器网络追踪系统中的一种高效位置更新机制（LUM）。在该机制中，移动节点只通过远程代理和近程代理这两种代理节点来更新位置信息。为验证该机制的性能，在真实的实验室环境中布置一个包含38个Micaz节点的原型系统。实验结果显示，与传统方法相比，LUM能够平均减少45％的消息发送和48％的能量消耗。

英文摘要：

In traditional tracking systems, the mobiles report their location to server periodically, which will result in high packet loss rate and rapid energy depletion as the number of mobiles increase. Actually, in practical tracking applications, it is observed that nodes are often close to others. Hence, it is conceived to pick out some nodes to report periodically as delegates for their adjacent ones. By exploiting this thought, an effective location updating mechanism （LUM） is proposed for tracking systems in wireless sensor network. In this method, mobiles update location information through two kinds of delegates： remote and nearby delegates. Remote delegates are infrastructure nodes appointed by server. Nearby delegates are heads of clusters constructed according to the RSSI （received signal strength indicator） values. In LUM, only delegates report location periodically instead of each mobile node. Therefore, LUM can save energy greatly through reducing the message complexity. However, in practical environment, signal fluctuations will affect the process of LUM. In order to solve this problem, the parameterized flip-flop filter and strap thresholds methods are developed to smooth and stabilize the RSSI values respectively. To demonstrate the performance of LUM, a prototype system with 38 Micaz nodes are deployed. The results show that LUM outperforms traditional approaches by at least 45% less message transmission and 48% fewer energy depletion on average.