無線感應網路(wireless sensor networks)就是結合大量的無限感應節點(sensor nodes)共同去執行同一個應用程式,例如環境監測, 健康追蹤, 侵入偵測等. 一般來說, 感應節點都是依賴電池來運作, 所以它們的電力非常有限.通常我們都假設感應節點一旦被佈置後就無法再重新充電. 因此在近幾年來, 很多研究者都著力在如何設計一個有效的省電機制來結合媒體存取控制協定(MAC)來達到能源節省, 以致於盡可能的延長整個感應網路的生命週期.之前的研究有一部分都著重在分時媒體存取協定(TDMA)的改進, 因為他擁有與生俱來的好的特性, 就是感應節點只須在固定的時槽(time slot)醒過來接收資料或傳送資料, 至於其他的時間就可以進入省電機制. 因此, 這樣一來它就不需要像競爭媒體存取協定(CSMA)還需另外再開發一個省電機制來結合其協定來跑.除此之外, 感應網路還有一個特性就是它是所有的感應節點都執行同一個應用, 所以例如我們叫感應節點去做溫度探測, 然後傳回環境溫度的最大值時,其實我們可以在這感應網路再做一個叢集(cluster)的架構, 這樣一來, 叢集的資料收集者(cluster-head)可以先做一個資料融合(data fusion)處理, 例如我們舉的溫度探測的例子, 從一大堆資料中我們可以直接算得一個溫度的最大值, 然後傳出一個最大值就好. 因此, 就可以節省傳輸大量資料所需花費的電力. 所以, 分時媒體存取協定再搭配叢集機制就可以大大的有效達到省電的目標. 但是在這之中我們發現了一個重大的問題會嚴重導致系統效率下降, 那就是資料收集者 (cluster-head)在收集資料當中會常常受到閘道器(gateway)的碰撞(collision)的影響而導致收到的資料不能解碼, 造成資料遺失, 換句話說就是當下傳的這一筆資料是沒效的, 進而相同於浪費電力去傳這一筆資料, 我們稱這種問題叫做多重交錯叢集(multiple-cluster collision)問題. 而且, 隨著越多閘道器的存在,系統效能就下降的越嚴重. 因此在此篇論文中我們提出一個分散式的方法,且完全解決這個碰撞所造成資料遺失的問題. 最後, 我們會跟之前的論文作相比以證明我們所提出的方法在, 碰撞降低, 單位時間資料產量(throughput), 可獲的巨大的改善

Wireless sensor networks typically consist of a significant number of low-cost sensor nodes which can collaborate among each other to execute a wide range of applications, such as environmental and health monitoring, intrusion detection, etc. Basically, sensor nodes are mainly battery-powered and have a limited amount of energy to spend, thereby they are not likely to be recharged or replenished after being deployed in an inaccessible sensed environment. As a result, in the past decade, power saving has become a critical issue for the design of a media access control (MAC) protocol in wireless sensor networks. By incorporating power-saving mechanism into MAC, we expect to maximize the lifetime of a sensor network. Intuitively, a large amount of research tends to make use of the TDMA protocol because it has inherently more favorable characteristics when compared to the CSMA protocol, that is, sensor nodes only need to wake up to transmit or receive data at its allocated time slots, and other time slots they can go into sleep mode. By doing so, it can reduce power consumption. However, in this master thesis, we found that there exists a rather acute problem, called the Multiple-Cluster Collision (MCC) problem, in the TDMA cluster-based protocol that will degrade the system performance drastically. Therefore, in this thesis, we propose the approach, called Multiple Cluster Collision Problem (MCCP), to perfectly eliminate the MCC problem by sensor nodes. Finally, we will compare our approach with SRSA, proposed by Tao WU et al., to show that the performance of our approach outperforms SRSA in terms of collision reduction, throughput and so on.

Content page
中文摘要……..…………………………………………………………….. i
Abstract………….…………………………………………...................... iii
List of Figures .………………………………………………...…………. vii
Content ……………………………………………………......................... v
Chapter 1 Introduction……………………………………………….. 1
1-1 Overview……………………………............................. 1
1-2 Motivation …………..................................................... 2
1-3 Thesis Organization …………...................................... 3
Chapter 2 Related Works…………………………………………….. 4
2-1 CSMA Protocol with Power Saving Mechanism … 4 2.2 TDMA Protocol with Cluster-Based Policy………. 5
2-3 Cross-Layer Design……………………....………… 6
2-4 Multiple Cluster Collision Problem ………………. 7
Chapter 3 Proposed Scheme………………………………………. 9
3-1 Network Model and Assumptions………………… 9
3.2 Problem Definition……………………………….. 12
3.3 Multiple Cluster Collision Avoidance ……………. 15
3.4 An example……………………………………….. 25
3.5 Refinement of Our Proposed Scheme…………. 29
3.5.1 Fairness Problem………………………… 29
3.5.2 Unbound Repeat Collision Problem……. 30
Chapter 4 Performance Evaluation……………………………… 33
Chapter 5 Conclusion and Future Work………………………… 41
References…………………………………………………………….. 43

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