無線感測網路是近年備受矚目的研究領域，可應用的範圍廣泛，例如: 監測環境、目標追蹤和科學探測，而這些應用都是屬於長時間的應用，但因感測器的電量是有限的，電量耗盡後要再充電或是更換來維持應用的執行並不是容易的事，所以有效減少感測器開啟的時間來延長整個應用是很重要的議題。解決方案之一是讓整個無線感測網路以低工作週期的方式來運行，好處是能有效的減少能源消耗的問題，但當感測器偵測到環境變化時要將資料傳至匯節點的延遲會增加，因每一個的感測器大部分的時間都是休眠的狀態，只有少部份的時間為活動的狀態。所以如何設計感測器活動的時間來降低傳送延遲變得非常重要。在本篇論文中提出了一個基於感測器的梯度來設計活動時間槽的機制 (GRASS)，提出的演算法發分為三個步驟，(1) 建立梯度 (2) 設定活動時間槽 (3) 以此資訊來做路由。最後模擬結果顯示，本論文提出的方法在傳輸的時間和空間上取得一致性，進而可以比其他機制花費更少的傳送延遲和傳送次數。

Wireless Sensor Networks (WSNs) have been gotten much attention in recent years. In WSNs, energy consumption is the critical issue. Long-term applications, such as environmental monitoring, scientific surveillance, and target tracking require networks to manipulate for long time. However, sensor nodes are powered by batteries which are irreplaceable and limited energy when finishing deploying sensor nodes. Since, it is an important issue to decrease time of sensor nodes in active state in order to prolong the life time of sensor nodes, which means that using low-duty-cycle manner in WSNs. The advantage of low-duty-cycle is to reduce the energy consumption effectively. However, the delivery latency of sending packets from sensor nodes to the sink is much longer than traditional WSNs because sensor nodes are dormant state most of time and wake up to receive packets in routine. Therefore, it is significantly to design active slot scheduling of sensor nodes, which is a critical issue in the low-duty-cycle WSNs. In this thesis, the GRadient-based and Active Slot Scheduling (GRASS) algorithm is proposed to reduce the end-to-end delivery latency in the low-duty-cycle WSNs environment. The proposed algorithm consists mainly of three steps. First, gradient establishment for the environment is performed. Next, set the active slot schedule based on the gradient. Finally, route the packet by forwarding set. The simulation results show that GRASS algorithm accomplishes consistency in temporal and spatial. Moreover, the proposed algorithm requires less delivery latency and the number of transmission compared with other two schemes for the packet of end-to-end delivery latency.

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