無線感測器網路 (Wireless sensor networks) 在近幾年來已經成為一個有趣且重要的研究領域，如同所有分散式系統，時間同步在無線感測器網路中是一個很重要的議題，而感測器 (sensor nodes) 之間是利用加上時戳的訊息完成時間同步，但是訊息在加上時戳後的傳輸過程中仍存在一些延遲時間，這些延遲時間長短是不固定的，且會直接影響時間同步的精準度。除此之外，clock drift也是影響時間同步效能的一個重要因素，因此在這篇論文中，我們主要著重在探討clock drift和這些不固定的延遲時間對時間同步效能的影響，這些不確定時間長度的延遲時間包括encoding time、decoding time以及propagation time等。我們將比較幾個時間同步協定在clock drift和這些延遲時間影響下的效能，此外，我們也探討這些協定是如何消除或降低延遲時間所造成的影響。 Wireless sensor networks (WSNs) have emerged as an interesting and important research area in the last few years. As in all distributed systems, time synchronization plays a key role in wireless sensor networks. Time synchronization is realized by those messages that are time-stamped. But there are several delay times during transmission after time stamping. These delay times are uncertain and contribute directly to synchronization error. The uncertainties include encoding time, decoding time, propagation time, and system calls. In addition to the uncertainties, clock drift is also a main source of time synchronization error. In this thesis, we propose a time synchronization protocol and study the influence of clock drift and uncertainties on various time synchronization protocols. We compare and evaluate the performance of our proposed protocol to previous works with clock drift and various uncertainties. In addition, we study how those protocols can reduce or eliminate the effect of the uncertainties.
