非同步工作週期無線感測網路具廣域延遲資訊路由協定;Extensively Delay-Aware Routing in Asynchronous Duty Cycle Wireless Sensor Networks

[[abstract]]在無線感測網路中，能源效率之設計是一個重要的議題且已經有多年的研究。為了節省能源，工作週期的機制已被提出來解決能源問題。工作週期意思是感測器節點能透過它們的工作時間表來決定在短期間內維持醒著以進行資料傳送，相反的，感測器節點會利用剩餘期間進入睡眠以達到省電。工作週期又可以分成兩種，同步工作週期與非同步工作週期。在同步工作週期中，感測器節點會彼此協同在相同期間醒來以傳送資料，然而，為了達成這個目的，感測器節點必須交換彼此的工作時間表造成額外的封包成本。因此，提出了非同步工作週期。在這種型態中，感測器節點會獨立決定它們的工作時間表，所以容易佈建且無額外成本。但是，問題是感測器節點在有資料要傳時需要等待其中一個鄰居節點醒來以接收資料，在論文中我們稱這段等待時間為睡眠延遲。如果在每個節點間都有睡眠延遲，將會造成點到點延遲。有一先前研究就提出了分散式的方法來解決這個問題。他們利用sink節點透過生成樹廣播封包到整個網路讓每個感測器節點收集延遲資訊，所以每個感測器節點能得知如果它們透過鄰居節點傳送資料到sink節點的點到點延遲。然而，每個感測器節點如果透過生成樹來收集只能得到sink節點方向的延遲資訊。因此，我們在這篇論文中提出了廣域延遲資訊路由協定。首先，我們在感測器節點有相同工作週期的簡單環境提出了最佳解。再者，我們在感測器節點有不同工作週期的環境再提出兩個不同的路由協定。模擬實驗結果顯示出我們方法比先前研究有更短的點到點延遲。 In wireless sensor networks, energy efficient design is an important issue and has been researched in many years. In order to save energy, duty cycle scheme is proposed to solve the energy problem. Duty cycle means the sensor nodes can decide to keep awake for data transmission in a short time period according to their working schedule, on the other hand, for the remaining time period, sensor nodes turn into sleep mode for saving energy. It is divided into two types, synchronous duty cycle and asynchronous duty cycle. In synchronous duty cycle, sensor nodes cooperate with each other to stay awake in the same time period to transmit data, however, to achieve this purpose, sensor nodes need to exchange their working schedule so that there is additional packet overhead. Therefore, asynchronous duty cycle is proposed. In this type, sensor nodes determine their working schedule independently, so it is easy to deploy and there is no extra cost. However, the problem is that sensor nodes have to wait for one of their neighbor nodes wake up to receive when they have data to send, we call the waiting time as sleep latency in this paper. If there is sleep latency between each hop, it will cause long end-to-end delay. A previous work proposed a distributed solution to solve this problem. They use sink node to broadcast a packet through a spanning tree to the whole network to collect delay information for each sensor node, so every sensor nodes can know the end-to-end delay if they transmit data to sink node through their neighbor nodes. Nevertheless, each sensor nodes can only get the delay information of the direction to sink node if they collect the delay information through a spanning tree. Therefore, we propose Extensively Delay-Aware Routing in this paper. First, we propose an optimal solution in easy environment, which sensor nodes have the same working cycle. Second, we further propose two different routing protocols in different working cycle of sensor nodes environment. Simulation results show that our method has lower end-to-end delay than previous work