利用網路編碼改善無線感測網路下傳輸資料的可靠性

Abstract

無線感測網路(Wireless Sensor Networks)廣泛應用在環境偵測、遠距離看護系統、軍事監測、災難救援偵測等等。無線感測網路受到資源上的限制，例如：電量、頻寬、記憶體以及計算速度。然而，無線感測網路在運作過程中由於電量上的限制，在加上無線網路中訊號強度的改變，電波干擾等因素影響使得感測器失去功能進而產生封包遺失的問題。是以無線感測網路的可靠性是一個仍須探討的議題。網路編碼(Network Coding)，近年來為一熱門研究主題，企圖利用中繼點將所收到的封包加以編碼，使得接收端在收到足夠的封包時自己便能自行解碼。 在此篇論文中，我們考慮在不使用傳統的ARQ機制下，利用有限度的泛播(Flooding)以及有限度的重傳次數，改善無線感測網路資料傳輸的可靠性。並且結合網路編碼在多個中繼點編碼，達到資料擴散至節點之間的目的。是以，透過時間分集(time diversity)以及空間分集(space diversity)的方式，進而提升無線感測網路的可靠性。實驗結果顯示，我們所提出的方法的確有效提升封包到達率。Wireless sensor networks have been widely used in many applications such as environmental monitoring, health-care monitoring, military monitoring, disaster management, etc. Sensor nodes are constrained by energy, computational capability and storage space. Such constraints, signal strength, and interference may cause node failure, link failure and result in the problem of packet loss. Therefore, how to provide a reliable data transmission in wireless sensor networks is still a challenging issue. Network coding, a popular research topic for years, is one of techniques attempting to encode packets for transmission at a node or relay station. After the relay station sends the encoded packet, a receiver can successfully decode the packet when it received enough encoded packets. In this thesis, we consider limited flooding and multiple transmissions techniques to counter the loss of reliability when traditional ARQ techniques are not employed. Furthermore, we apply network coding to encode buffered packets at rely stations. Taking advantage of time diversity from limited flooding and multiple transmission and Taking advantage of space diversity from network coding, we thus can improve the reliability in data transmission in wireless sensor networks. We show simulation results on packet delivery ratio to validate the purpose methods.