最近科技的進步，使低成本、低電量消耗的無線感測網路可以實現。時間同步對於分散式系統是很重要的服務，包括感測網路系統。時間同步可以用於省電機制上，例如IEEE 802.11 的電量省電模式(Power Saving Mode;PSM)也是透過時間同步功能(Timing Synchronization Function；TSF)為基礎，來達到省電。無線感測網路的電力來源為電池，無線感測網路被佈置在外面環境中，大多不再回收，因此為增加感測網路的生命，省電機制更加重要。本論文探討時間同步的問題，希望用較省電的方法達到時間同步目的。我們針對無線感測網路的環境下提出ETSP (Efficient Timing Synchronization Protocol)時間同步，我們利用無線感測網路不會移動的特性，減少節點傳送時間同步信標，並週期一段時間再重作時間同步。IEEE 802.11 TSF時間同步採用持續性傳送信標，這過程中會消耗大量電力。 ETSP採取有次數限制的發送信標，並在已被時間同步區域的節點，也採取不發送信標來節省電量。ETSP在模擬實驗驗證可以節省電力，並且可以讓各節點電量消耗平均，我們在實體無線感測網路實作驗證可行性。

Recent advances in technology have made low cost, lower power wireless sensor a reality. Clock synchronization is an important service in any distributed system, including sensor network system. Time synchronization may use in the saving power mechanism. For instance IEEE 802.11 PSM is penetrates time synchronization TSF is a foundation, then achieve the saving power. The wireless sensor network the electric power origin is a battery. The wireless sensor network is put down in the outside environment, mostly no longer recycles. Therefore for increases the wireless sensor network the life, saves the electricity mechanism to be more important. The present paper discussion time synchronization question, hoped with comparatively saves the electricity the method to achieve the time synchronization goal. We propose an Efficient Timing Synchronization Protocol (ETSP) in view of under the wireless sensor network environment. We use the wireless sensor network cannot move the characteristic, reduces the node transmission time synchronization beacon. And is cyclic period of time to redo time synchronization again. IEEE 802.11 TSF time synchronization uses the long-enduring transmission beacon. In this process can consume the massive electric powers. ETSP adopts has the transmission beacon which the number of times limits. And in already by time synchronization node, also adopts does not transmit the beacon to save the electric quantity. ETSP confirms at the experiment may save the electric power, and may let various pitch points electric quantity consumption average. We in the entity wireless sensor network really makes the confirmation feasibility.

目錄
第一章 序論 1
1.1研究背景 1
1.2研究目的 2
1.3論文章節架構 3
第二章 文獻探討 4
2.1 IEEE 802.11 4
2.2 Automatic Synchronization Procedure（ASP） 6
第三章 時間同步協定設計 10
3.1 時間同步的議題 10
3.2  ETSP（Efficient Timing Synchronization Protocol） 12
3.3  ETSP的時間同步步驟 13
3.4 新點加入步驟 16
3.5 時間偏移問題 16
第四章 效能分析 18
4.1 傳送信標次數 19
4.2 多個起始點個數 20
4.3 時間同步速度 20
4.4 電量消耗 21
4.5 節點存活比較 22
4.6 最大時間偏移 23
4.7 實作結果 25
第五章 結論及未來展望 28
參考文獻 29
附錄一、無線感測網路實作 32

圖目錄
圖1：信標產生視窗 5
圖2：時間同步關鍵路徑 11
圖3：時間同步示意圖 13
圖4：有限次數傳送信標 19
圖5：多個起始點個數成功機率圖 20
圖6：時間同步速度比較圖 21
圖7：節點累積電力耗損圖 22
圖8：尚有電量節點個數比較圖 23
圖9a：TSF最大時間偏移 24
圖9b：ASP最大時間偏移 24
圖9c：ETSP最大時間偏移 24
圖10：模擬最大時間偏移圖 25
圖11a：實作無線感測網路最大時間偏移(ts=60分）27
圖11b：實作無線感測網路最大時間偏移（ts=120分）27
圖11c：實作無線感測網路最大時間偏移（ts=180分）27
圖12：硬體架構 32
圖13a：Mica2 33
圖13b：感測器 33
圖13c：程式板 33
圖14：CC1000Const.h程式碼 34
圖15：ETSP.nc程式碼 35
圖16：編譯程式 36
圖17：編譯完成 37
圖18：Mica2與程式板連結 37
圖19：程式燒錄指令範例 38
圖20：燒錄程式到Mica2 39
圖21：燒錄成功訊息 39
圖22：利用Java擷取資料示意圖 40
圖23：利用Java擷取時間同步 40

表目錄
表1：模擬環境參數 18
表2：實作環境列表 26
表3：常用頻率表 35

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