無線感測網路（wireless sensor network）是由一群大量的感測節點（sensor node）所組成。感測節點部署在一固定區域，負責將其所感測到的資訊傳送到基地台（base station）。而感測網路所面臨到的一個嚴重問題就是有限的電力，因此如何有效節省電力，提升網路的存活時間，便是我們所要努力的目標。
　　其中有不少研究利用感測節點有其感測範圍（sensing range）的特性，藉由睡眠排程(sleeping schedule)關掉多餘的感測節點（其感測範圍可被其他節點所覆蓋），維持感測網路原本的覆蓋率（coverage），來節省掉不必要的電力耗損，進而延長感測網路的生命週期。但若要精確的找出這些多餘的感測節點，勢必要裝載定位系統或指向性天線，這對於感測網路而言，必須要付出相當大的成本代價。而且並不是所有的感測網路，都需要如此嚴謹的覆蓋率。
　　我們在無網感測網路中提出一個分散式的排程法則，利用空間性的群組（group），並對同一群組內的感測節點進行排程(node scheduling)，讓它們可以輪流運作，最後根據節點的電力負載來建立路由(routing)。透過這樣的方法，我們只犧牲了些微的覆蓋率，來讓網路可以關掉更多的節點，節省更多的電力。實驗結果顯示，在密度比較高的網路拓撲下，我們的覆蓋率可以非常接近100%，並讓感測網路的生命週期可以大大地提升。

In Wireless sensor networks, sensor nodes are deployed to monitor some environmental parameters and send them to the base station. The energy of sensor nodes is a critical resource in wireless sensor network. It is important to prolong the lifetime of the network.
In order to reduce network overall energy consumption, some research presents schemes to turn off part of sensor nodes with guarantee of sufficient sensing coverage and reliability. To find out the redundant nodes, the scheme needs to equip sensor nodes with GPS or directional antenna which is however costly.
We propose a distributed approach to turn off more nodes at a slight cost of coverage. We divide nodes into several groups according to their first association with some random selected node. Those sensors in the same group are scheduled so that only one node is active and responsible for monitoring environmental parameters every time. Based on their residual energy, routing paths are built to connect those active nodes to the base station. Simulation results show that our approach can extend the network life time only at a little cost of coverage in the high density topology network.

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