真實多跳階無線網路系統之切頻與繞徑機制問題研究

Abstract

在多通道無線網路中一項重要的效能議題是如何有效率地利用通道的多樣性達成平 行通訊。在多通道無線網路系統中，節點對無線網路介面上的所有可用通道進行切換，雖然會多了通道切換的延遲時間和可能造成節點彼此間不連結的情況，卻比永久綁定使用同一個頻道有更佳的通道多樣性。此外，因為無線網路介面上的通道在進行切換，多跳階傳輸會面臨挑戰如在探索路徑時，節點之間缺少在同通道中共同交會的時間和節點之間彼此傳送封包的困難。上述的觀察促使我們提出一個支援多個無線網路介面的通道跳頻機制(CHS)來保持良好的網路連線。在目前普遍使用的IEEE 802.11為基礎的無線網路中，我們證明CHS可以在節點有少於三個無線網路介面的情形下可以達到良好的通道重疊性。我們也設計了相應的多通道路由協議(CDR)促使CHS在通道跳躍的情況下能達到有效率的多跳階傳輸。在本論文中，我們使用一個開放原始碼的路由軟體進一步實現所提出的CHS和CDR機制於真實多跳階網路架構裡。實作的結果顯示我們提出的CDR 配合CHS 會優於其他的基於IEEE 802.11b/g 的多跳階網路環境的方法，也證實了CDR在真實環境下的實用性。

One essential performance problem in multi-channel wireless networks is how to effectively exploit channel diversity to enable parallel communications. For a wireless system with multiple orthogonal (non-overlapping) channels available, having a radio interface hop through all available channels produces better spectrum diversity than binding it permanently to one channel, at the cost of channel switching delays and potentially compromised network connectivity. Moreover, multi-hop communications become challenging due to the lack of a common rendezvous for discovering routes and the difficulty of relaying packets from hop to hop. The above observations motivated us to propose a multi-radio channel-hopping scheme (CHS) that preserves network connectivity. We proved that less than three radios are required by CHS in order to achieve good channel overlapping in widespread IEEE 802.11-based wireless systems. Corresponding channel-diverse routing (CDR) protocol was devised to realize efficient multi-hop communications. In this thesis, we further implemented the proposed CHS and CDR mechanisms in a real multi-hop wireless networking prototype based on an open-source router software. Empirical results demonstrate that the proposed CDR outperforms other strategies in static IEEE 802.11b/g multi-hop networking environments, and corroborate the practicality of CDR in real networks.