無線傳感器網路依預定時間之事件排序機制

Event Ordering by Predefined Time for Wireless Sensor and Actor Networks

許峻豪(Chun-Hao Hsu)

指導教授 ： 段裘慶

國立臺北科技大學/電資學院/電腦與通訊研究所/碩士(2010年)

摘要

於無線傳感器網路中，因為具有反應節點可以提供即時的事件處理，當事件間具有時間相依關係時，就可依照其相依關係依序作處理。相關研究之事件排序機制，大多依賴確認訊息回覆來判斷時間順序的正確性，當節點失效或節點間連結斷裂時，易造成確認訊息回覆上的失序，導致事件處理產生錯誤。
為此本研究提出預定時間事件排序機制，以解決遇到節點失效或連結斷裂產生的問題，此機制將記錄於反應節點通訊範圍內，所有感測節點傳回訊息至反應節點所需之最長時間。當反應節點接收到的感測事件，依初始記錄的路由最長時間可確認傳回之感測事件的時間順序，作正確時序的處理，可避免當路徑上的節點失效或節點間連結斷裂時，無法接收到確認訊息而發生執行順序的錯誤。
效能分析上，於確認排序機制及單一事件排序機制進行效能評估，並定義事件排序正確率、平均事件處理時間與平均傳遞訊息數為量測指標。
模擬結果得知，事件排序正確方面，於連結斷裂實驗下(節點失效數比率為25%)，預定時間事件排序機制比確認排序機制與單一事件排序機制高出13%。平均事件處理時間方面(環境範圍為2002 m2)，預定時間事件排序機制比確認排序機制多9.4%，比單一事件排序機制減少38.3%；平均傳遞訊息數方面預定時間事件排序機制皆優於確認排序機制與單一事件排序機制。

關鍵字

無線傳感器網路 ； 反應節點 ； 事件排序機制 ； 預定時間

並列摘要

In Wireless Sensor and Actor Networks (WSAN), actors can supply real-time event handling, thus when events have the time dependent relationship, events related to others can be processed in a correct order. Related researches on event ordering mechanism, most rely on confirmation messages to determine the correctness of event time-order. However, repling to the confirmation message by nodes easily cause the failure when one the node or link failure.
Therefore, this paper proposed an Event Ordering by Predefined Time (EOPT) mechanism to solve the problem of node or link failure, EOPT first records the time of all sensor nodes reply the Transmition-time message (Mt) back to the actor. Then EOPT will solve the problem by Longest Leaf-node Time (LLT), that the maximum time for sending Mt to the actor.
In performance analysis, we compare the performance of EOPT with Ordering by Confirmation (OBC) mechanism and Simplex Event Ordering (SEO) mechanism. We also define three metrics: Average transmition message (Mavg), Average time for event handling (Tavg ) and Rate of correct for event ordering (Rc).
From the simulation results, in the experiment under the number of nodes failure rate (Rd) of 25%, EOPT was better than OBC and SEO by 13% on the Rc. In the experiment under the environmental range of 2002 m2, OBC was better than EOPT by 9.4% on the Tavg, but EOPT was better than SEO by 38.3% on the Tavg. Moreover, EOPT outperformed OBC and SEO on the Mavg.

並列關鍵字

Wireless Sensor and Actor Networks ； Actor ； Event Ordering ； Predefined Time

參考文獻

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