節能之水下網路機率式路由設計

Abstract

近年來水下感測網路漸漸被廣泛討論及研究，各種應用也隨之而生。水下感測網路利用的是聲波，因為水是高頻的濾波器，如果利用電磁波傳遞，訊號會衰減的很快。對於不同的水下感測網路的應用需求也會不同，必須考量的條件也不同，例如長時間水下監控的應用或是即時的通訊應用，必須考量電源的使用效率或是縮短傳輸延遲。但是由於陸地上感測網路與水下感測網路的傳輸介質不同，水下感測網路對於對於電源使用效率或是縮短傳輸延遲的路由設計，不能以陸地上感測網路的環境所設計的路由設計，直接套用在水下感測網路。 機率式路由[1] 的概念已經被廣為應用，在無線感測網路中增進資料傳輸效率也已被普遍認同。機率式路由利用無線網路廣播的特性，從相鄰節點中找出一個較好的節點進行封包傳送。在本篇論文中我們結合機率式路由的概念，針對長時間的水下監控應用和即時水下通訊應用，提出了分別適用這兩個應用的路由演算法。首先，我們針對即時水下通訊應用提出延遲容忍之水下機率式路由協定，稱為UWOR。點對點間的延遲是影響水下即時通訊應用重要的因素之一，UWOR 在滿足給定之點對點容忍延遲條件下，去最大化在期限內所收到的封包數量，同時UWOR 也考慮點對點封包傳輸時所消耗的電源。最後，我們針對長時間水下監控應用提出非同步睡眠-喚醒排程之水下機率式路由協定，稱為UWASSOR。UWASSOR 的目標是要讓水下長時間間監控的應用延長其網路運作時間。UWASSOR 同時考慮睡眠-喚醒排程與機率式路由，其中睡眠-喚醒排程可以減少電源的消耗，因為當節點在沒有傳輸或是接收資料時進入睡眠模式可以減少電源的消耗，最後我們藉由實驗驗證睡眠-喚醒排程與機率式路由可達到延長網路運作時間的目標。

Underwater sensor networks (UWSNs) have received growing interests recently. In UWSNs, acoustic channel is used as the communication method. Such networks, due to the need for different applications, such that long-term monitoring or time critical communication must be delay aware or energy efficient depends on the applications. However, there are fundamental differences between radio interfaces and acoustic modems. The characteristics of UWSNs and the requirements for energy efficiency or delay-aware make the exist routing protocols difficult to directly adapt ideas which have already been proven reliable in terrestrial sensor networks. Opportunistic routing [1] (OR) takes advantages of the spatial diversity and broadcast nature of wireless networks to combat the time-varying links by involving multiple neighboring nodes (forwarding candidates) for each packet relay. In this thesis, we integrated the idea of opportunistic-based routing and proposed two routing protocols for two types of UWSNs applications: time-critical aquatic exploration and long-term aquatic monitoring. The first routing protocol is called Delay-Sensitive Opportunistic Routing for Underwater Sensor Networks (UWOR). End-to-end latency is one of the key elements for delay-sensitive UWSNs applications. UWOR maximizes data goodput while satisfying end-to-end latency requirements of time-critical aquatic exploration applications in UWSNs. UWOR focuses on two metrics for UWSNs: goodput and energy cost. Goodput is used to measure the amount of data received before the deadline, and energy accounts for end-to-end per-packet energy consumption. The second routing protocol is call Asynchronous Sleep-wake Scheduling and Opportunistic Routing for Underwater Sensor Networks (UWASSOR). In UWASSOR, we jointly consider the sleep-awake scheduling and opportunistic-based routing into underwater routing. Sleep-wake scheduling can reduce the energy consumption because sensor nodes can enter sleep mode while there is no packet to send or relay. Our goal is to maximum the network lifetime for long-term aquatic monitoring applications.