在隨意式無線網路下使用功率為量測標準且具有容錯機制的穩定繞送演算法

A Fault-Tolerance Embedded Stable Routing Algorithm based on Signal Strength in Ad Hoc Wireless Networks

謝耀章(Yao-Chang Hsieh)

指導教授 ： 黃依賢

元智大學/資訊學院/資訊工程學系/碩士(2001年)

摘要

隨意式無線網路(Ad Hoc wireless networks)是一種新的網路型態，和一般無線網路環境比較，它不需要有基地台(base station)的架構，而是透過網路上的某些移動台(mobile host)傳遞資料。每個移動台就好像動態的(dynamic)基地台一般，提供路由的機制。由於具有移動性(mobility)的特性，從來源端到目的端的傳輸路徑，會因為某個移動台移動而使得整條路徑斷線。此時，來源端或中間節點必須花費額外的時間找出一條新的路徑來傳遞資料。為了補救此狀況發生，我們提出一個以訊號強度為感測且具有容錯(fault tolerance)機制的穩定繞送演算法。依接收端所感測的訊號強度(signal strength)，定出兩個高、低門檻值(threshold)，來作為判定穩定鍊結的依據。當鍊結的訊號強度大於高門檻值時，表示兩節點非常接近，會造成此路徑的跳躍數(number of hops)增加；反之，當鍊結的訊號強度小於低門檻值時，表示接收端正處於傳輸範圍的臨界點，增加路徑斷線的機率。因此，我們定義所謂的穩定鍊結為接收的訊號強度介於兩門檻值之間且瞬間訊號強度變化趨近於零，利用這些穩定的鍊結從來源端(source node)傳遞資料到目的端(destination node)。除了使用第一條最穩定路徑(stable routing path)外，我們使用容錯機制來找出其他可用的穩定路徑來增加繞送穩定度。最後，撰寫模擬程式驗證以及比較其他演算法。

關鍵字

隨意式無線網路 ； 移動性 ； 訊號強度 ； 穩定路徑 ； 容錯

並列摘要

Ad Hoc wireless networks are novel networks. Compared with infrastructure wireless LAN, packets are not passed by base stations or access points, but are through some mobile hosts in Ad Hoc wireless networks. Because of the characteristic of the mobility, path from source node to destination node will be dropped frequently. Source node or intermediate node must cost the additional time to find out a new path. For rectifying this condition, a Fault-Tolerance Embedded Stable Routing Algorithm based on signal strength is proposed. According to the signal strength detected by receiver, high signal threshold and low signal threshold are defined to judge whether link is stable or not. When signal strength between two nodes is greater than high signal threshold, it means that the two nodes move closer. The number of hop will be increased if there are many these links in a path. Whereas, when signal strength is smaller than low signal threshold, it shows that the two nodes are faraway. Dropping probability will be increased if there are many these links in a path. Consequently, the definition of stable link follows: (i) signal strength is between high and low signal thresholds and (ii) the variation of twinkling signal strength is equal to zero. A path with these stable links will result in low dropping probability. Besides, a fault-tolerance technique is to find out other available stable path and increase routing stability. Finally, simulation results indicate that our algorithm gets lower path dropping probability than shortest path algorithm.

並列關鍵字

Ad Hoc wireless network ； mobility ； signal strength ； stable routing path ； fault tolerance

參考文獻

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