時間同步(Time Synchronization)為無線感測網路(Wireless Sensor Network)中一重要的研究議題，諸如物體移動的追蹤、視覺影像的監控與比對或是利用TDMA的MAC排程等，都必須在時間同步的條件下進行。傳統的時間同步技術主要是討論感測器之間如何進行對時，使得感測器之間能夠有效的達到時間同步。然而，這類文獻的控制封包過多，且未考量時間同步的精準度與事件發生之時限關係，因此，這類文獻會有網路負載量過大及電量消耗過多的問題。本論文針對這些問題提出一時間同步技術，並且加入省電機制(Power Saving)，使得能夠減少感測器之耗電量。此外，我們還針對水下感測網路(Underwater Sensor Network)，提出一時間同步技術，使其能運作在較長傳輸延遲時間的環境下，且能夠減少同步所需的時間與傳送的封包量。模擬結果顯示，本論文所提出之時間同步技術確實可以有效的降低網路負載量，且達到延長整個感測網路之生命期的目標，並保證時間同步的精準度在一誤差水準之內。

Time Synchronization is an important issue in wireless sensor networks, such as target tracking, environment monitoring and TDMA MAC scheduling. This paper proposes a time synchronization technique for the wireless sensor networks. By applying the proposed time synchronization technique, the number of synchronization packets and energy consumption can be greatly reduced. This paper also proposes an efficient time synchronization technique for the underwater sensor network. By applying the proposed time synchronization technique, the synchronization duration and the number of synchronization packets can be greatly reduced. Simulation results show that the proposed technique outperforms existing schemes in terms of the synchronization accuracy, network and synchronization duration.

目錄	III
圖目錄	V
表目錄	VII
第一章、 簡介	1
第二章、 國內外相關研究	2
第三章、 在無線感測網路中具睡眠機制之時間同步技術	7
3.1 網路環境與問題描述	7
3.1.1 網路環境	7
3.1.2 問題描述	8
3.2 On-Demand Time Synchronization Mechanism	11
3.2.1 Initialization Phase	11
3.2.2 Power Saving phase	16
3.2.3 On-Demand Time Synchronization phase	19
3.3 實驗分析及模擬	27
3.3.1 模擬環境	27
3.3.2 實驗比較	27
第四章、 在水下感測網路中具效率之時間同步技術	35
4.1 網路環境與問題描述	35
4.1.1 網路環境	35
4.1.2 問題描述	35
4.2 Basic Efficient Time-Synchronization Technique (B-ETST)	37
4.2.1 Time packets exchange phase	37
4.2.2 Time synchronization phase	40
4.3 Enhanced Relay-based Time Synchronization Technique (E-RTST)	43
4.4 實驗分析及模擬	48
4.4.1 模擬環境	48
第五章、 結論	59
參考文獻	61
附錄-英文論文	63

圖目錄
圖(1)：切割完的監控區域及座標。	13
圖(2)：由BS建立的骨幹網路。	15
圖(3)：感測器si的工作及同步週期。	17
圖(4)：NS所在的六邊形網格種類	20
圖(5)：以圖(4)(b)為例，NS s1、s2與相鄰之BM BM3、BM4、BM5、BM6、BM7、BM8執行對時。	24
圖(6)：感測器各自經由JATP、FTSP、HRTS及PBS機制後的時間誤差分布。	28
圖(7)：感測器個數對同步精準度之影響。	29
圖(8)：感測器個數對網路負載量之影響。	30
圖(9)：各同步次數對同步封包數之影響。	31
圖(10)：感測器個數對電量消耗之影響。	32
圖(11)：各同步次數對電量消耗之影響。	33
圖(12)：感測器個數對最短及平均網路生命期之影響。	34
圖(13)：由BS開始執行時間同步程序。	39
圖(14)：考慮NS sj如何計算出與SS si之間的時間誤差。	40
圖(15)：由BS開始執行時間同步程序。	46
圖(16)：感測器各自經由B-ETST與E-RTST機制後的時間誤差分布。	49
圖(17)：感測器個數對同步精準度之影響。	50
圖(18)：感測器個數對網路負載量之影響。	51
圖(19)：感測器個數對同步所需時間之影響。	52
圖(20)：感測器個數對電量消耗之影響。	53
圖(21)：感測器各自經由B-ETST、E-RTST、TSHL及Tri-Message機制後的時間誤差分布。	54
圖(22)：感測器個數對同步精準度之影響。	55
圖(23)：感測器個數對網路負載量之影響。	56
圖(24)：感測器個數對同步所需時間之影響。	57
圖(25)：感測器個數對電量消耗之影響。	58

表目錄
表一：環境參數	27
表二：環境參數	48

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