針對方向性傳輸多頻道無線網狀網路之頻道指派及效能評估

Abstract

IEEE 802.11在不同技術中提供非重疊頻道攻平行傳輸使用，但大部份的無線網路仍採用單頻道進行傳輸，本論文針對單一頻道無線網路傳輸可能發生的訊號干擾、hidden terminal problem、exposed terminal problem做深入研究與探討，在不需要修改底層網路協定(MAC and PHY layer)以及架構的前提下，藉由修改系統程式以支援節點使用多張網卡同時傳輸，提升網路整體傳輸效能(Overall network goodput)，同時設計一套頻道指派演算法(Channel assignment algorithm)指派無線網路link所使用之傳輸頻道，藉由與其他頻道指派法比較展示頻道指派之重要性。同時針對無線格狀網路(wireless grid network)設計有別於使用指向型天線(directional antenna)的方向性傳輸機制(directional transmission)減低節點競爭無線link傳輸媒介可能發生的封包碰撞。 經過ns2模擬實驗驗證，我們提出的頻道指派演算法可大幅度提升傳統單一頻道的網路傳輸效能，並且提昇長路徑封包的傳遞成功率，在無線網路使用者不需要任何修改的情形下，採用我們所提出的架構以及方法可以提升無線網路使用者之網路使用經驗。

IEEE provides non-overlapping channels for multiple transmissions to transmit at the same time. But most IEEE 802.11-based networks today use only a single channel. As a result, these networks can’t exploit the peak performance because of packet collision and interference. In this thesis, we study the interference problems including hidden terminal problem and exposed terminal problem in wireless mesh networks. We proposed a new architecture of directional multi-channel wireless mesh networks and TwoHop channel assignment algorithm. Compared to the single-channel network, we only revise the systematic procedure to support the multi-channel transmission with multiple network interface cards to transmit at the same time. Using our channel assignment algorithm to assign channels on links can lower the interference problems in wireless LANs and improve the network overall received goodput. We verify the performance improvement of the proposed algorithm through ns2. From the result, our approaches indeed improve the network performance and the success rate of the long route packets.