在無集中控制的無線通訊環境當中，每個行動端點 (Mobile Host，MH) 需要依照同樣的時脈維持同步以避免資料的遺失。使用 IEEE 802.11 標準制定的時間同步方法，無法解決當網路中 MH量變大時，而產生的非同步情形，尤其在 Multi-Hop 的環境，更難有效控制非同步情形的發生。本篇論文提出自動校正時脈的演算法改進 IEEE 802.11 的時間同步方法，首先提高時脈較快的 MH 傳送 Beacon 成功的機率，讓慢的 MH 取得與快的 MH 的時脈差距，獲得自動校正的功能。同時將校正後的資訊經由 Multi-Hop 的環境傳送出去，維持整個無線網路的同步狀態。由模擬結果顯示，在大型無線網路中，我們提出的演算法較 IEEE 802.11 的時間同步方法，降低60% 的平均最大時脈差距，並且有效抑制的非同步的情形發生。 In wireless ad hoc networks which without centralize control, it is important that all mobile hosts are synchronized to a common clock to avoid data loss. IEEE 802.11 standards specified the clock synchronization method to solve the problem. But this method can't solve the scalability problem of wireless ad hoc networks, especially in a multi-hop {it mobile ad hoc networks (MANETs)}. In this paper, we proposed a clock automatic adjustment algorithm to solve the problem. First, we let the faster mobile hosts have high priority to send out the timing information. Then, the other mobile hosts got the difference from the faster one, and got the adjustment value to synchronize automatic to keep all mobile hosts are synchronized in a multi-hop MANET. Simulation results show that our clock automatic adjustment algorithm decrease 60\% average maximum clock drift of IEEE 802.11 synchronization method, and effective in reducing the occurring times of asynchronous cases in a large-scale multi-hop MANET.
