非對稱傳輸特性對無實體架構網路繞送之影響

Abstract

在Mobile Ad Hoc network (MANET)中，單向連結普遍存在於鄰近的節點之間，主要是由於設備的異質性，進而產生非對稱性的傳送功率與接收靈敏度。事實上，非對稱性傳輸現象的存在明顯的衝擊大多數MANET繞送演算法執行效率，主因在於這些繞送演算法中，多採用Flooding的方式進行路徑探勘，而每個節點在接收到訊息時，未檢查返回至訊息來源者的反向路徑是否存在，即進行訊息轉送，常因反向連線不存在而導致路徑無法成功的建立。為了解決這個問題，我們提出了一套Power-aware的方法，基本原理為在Flooding訊息中，我們加入傳送功率與接收靈敏度的資訊，節點可利用此資訊計算反向連結是否存在，當連結存在時再考慮是否轉送訊息，否則忽略訊息。從模擬結果中我們觀察到，非對稱性傳輸現象會嚴重的危害到MANET繞送演算的正常運作（如：AODV或DSR），而加入Power-aware的功能，能顯著地降低路徑探勘的延遲達數十甚至數百倍之多。

In a mobile ad hoc network (MANET), unidirectional links commonly exist between a pair of neighboring nodes if they are heterogeneous devices and showing asymmetric transmission power or reception sensitivity. In this thesis, we show that such asymmetric transmission phenomenon significantly impacts the efficiency of most of the existent routing algorithms proposed for MANET. This is because they usually employ a flooding mechanism for route discovery, where a node forwards a received message to others without checking the reversibility of the link from which that message was received. Consequently, we may fail to establish the route because of absence of reverse links. To solve this problem, we introduce a power-aware scheme. In principle, information of transmission power and reception sensitivity is carried in a flooding message, and upon receiving the message, a node can use this information to figure out whether the reverse link exists or not. Only when the reverse link exists, the node will consider forwarding the message, otherwise ignore it. From the simulation result, we observe that the asymmetric transmission may seriously jeopardize the MANET routing (such as AODV and DSR) and the proposed power-aware scheme can significantly reduce their route discovery latency in the order of several magnitudes.