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標題: | 在低工作週期的物聯網中穩定廣播的省電協定 An Energy-Efficient Protocol for Reliable Broadcasting in Low-Duty Cycle IoT |
作者: | Cheng-Han Wu 吳承翰 |
指導教授: | 周俊廷(Chun-Ting Chou) |
關鍵字: | 同步,省電,媒體存取控制協定, Synchronization,Energy-Efficiency,MAC Protocol, |
出版年 : | 2016 |
學位: | 碩士 |
摘要: | 隨著物聯網科技的成長,無線裝置的數量快速的增加。大部分的無線裝置,尤其是感測器,都是電池驅動的。要維護這麼大數量的電池驅動裝置是非常困難的。因此,延長這些無線裝置運作時間就成為一個有價值的研究領域。
低工作週期控制是一個減少能源消耗的普遍方法,其作法是週期的將無線裝置轉為睡覺模式。裝置在睡眠時將會失去傳送和接收無線封包的能力。如果設計的不適當,就會讓整個網路運作不正常,甚至癱瘓。就算設計的妥當,也一定會增加整個系統反應的延遲。所以目的在於,如何設計可以在不增加太多延遲的前提下,盡量提升省電的效率。 這種作法已經存在許多研究成果,大致上可以把這些解法分為兩類,同步和非同步。在非同步解法中,裝置不會交換任何時間資訊。使用非同步演算法的裝置會依照某種設定好的週期進入睡眠狀態,並且保證兩個裝置一定會在一個週期內同時醒來。然而這種演算法雖然保證了裝置之間的溝通,卻嚴重增加封包傳遞的延遲。相反地,同步演算法會在裝置運行時不斷交換時間資訊,盡量減少無謂的嘗試所造成的延遲增加。 在這篇論文中,我們利用同步演算法的概念設計了一個非常低工作週期的省電協定。首先,我們在無線網路的拓樸中建立樹狀結構,裝置會根據這個樹狀結構決定其醒睡週期。接著我們定義了超級訊框的架構,一個超級訊框即為一個週期,包含醒睡的週期。在醒的週期中,包含同步週期與資料週期,前者用於交換時間資訊和建立樹狀結構,後者用於傳送應用所需的封包。除此之外,我們設計了一個穩定洪泛的演算法。這個演算法包含了傳統洪泛演算法,還有重傳機制。最後,我們的核心是利用樹狀架構,讓多重跳接式網路的中間節點輪流醒來,以達到最佳的省電效率,同時確保封包的延遲能夠不被其睡眠影響。 我們和分布式基礎協定(非同步)和感知媒體存取控制協定(同步)兩種協定做比較。結果顯示,在同樣的省電效率下,我們的做法可以減少95%和60%的延遲。 With the growth of Internet of Things (IoT) technologies, the number of wireless devices increases rapidly. Most of them, especially sensors, are battery-powered. To maintain and manage such a huge amount of devices is a big problem. As a result, to prolong the lifetime of these battery-powered devices becomes a critical issue. Duty-cycle control is a common solution to reduce energy consumption by periodically turning devices into the sleep mode. When devices are in the sleep mode, they cannot transmit and receive frames. The worst design of duty-cycle control mechanisms is that the network cannot work normally if devices always wake up at different time. Even they may wake up at the same time, transmission delay increases if their sleeps are not scheduled properly. Duty-cycle control mechanisms can be categorized as asynchronous and synchronous. Devices using asynchronous protocols do not exchange any timing information. They wake up with some special patterns so that it is guaranteed that wake up time of two devices overlap with each other. Although this category of protocols guarantees frame transmission, the increasing latency is an unsolved problem. On the contrary, synchronous protocols exchange time information so as to wake up simultaneously. As a result, the latency can be reduced. In this thesis, we design an energy-efficient protocol for the IoT network. The proposed protocol adopts the concept of synchronous duty-cycle control mechanisms. First, we design a parent discovery algorithm to construct a hierarchical structure. The synchronization is achieved with the help of the hierarchical structure. Second, we define a superframe structure to comstruct periodic wake-up and sleep periods. In wake-up periods, we design SYNC periods and DATA periods. The former is used to maintain the synchronization of the network, and the latter is used to exchange data frames. Third, we design a reliable flooding algorithm with implicit acknowledgement. This algorithm includes traditional flooding algorithm and a retransmission mechanism. Finally, the most important key of the proposed protocol is that, with the hierarchical structure, those devices which are relays of multi-hop transmissions take turns waking up to make sure the routes are unblocked. We compare our protocol with Quorum-based protocols (asynchronous ones) and S-MAC protocol (synchronous one). The result shows that, under the same duty-cycle constraint, our protocol can reduce end-to-end latency by 95% and 60% compare to grid-quorum protocol and S-MAC. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/60109 |
DOI: | 10.6342/NTU201603820 |
全文授權: | 有償授權 |
顯示於系所單位: | 電信工程學研究所 |
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