在基礎結構無線網路中，存在一個無線存取點(Access Point, AP)負責接收及傳送資料給其範圍下的節點(node)。由於傳輸效能會隨著節點與無線存取點之間的環境狀況而有所差異，因此，相較於連線品質較好的節點，當連線品質較差的節點獲得傳輸使用權時，需要更多的時間來傳輸同樣大小的封包，這使得其他節點要等待更久的時間才能重新競爭傳輸使用權，此現象使得整體傳輸效能會受到某些連線品質較差的節點所影響。
IEEE 802.11無線區域網路支援多頻道(multi-channel)的功能，在2.4 GHz的頻帶上，有三個互不相交(non-overlapping)的頻道可供使用。比起單頻道無線網路，多頻道無線網路提供所有節點更多的傳輸機會，整體的吞吐量(throughput)也會提高。但是，多頻道無線網路也產生了頻道配置(channel assignment)與頻道存取(channel access)的重要議題，過去諸多研究亦針對這些議題提出解決方法來改善整體的效能及網路使用率。
本論文針對整體傳輸效能會受到某些連線品質較差的節點所影響的問題，提出了一個在多頻道上以轉送為基礎的合作式傳輸(cooperative communication)媒體存取控制層(MAC layer)的協定，對於每一個連線，來源節點透過訊息交換以決定一個適合的鄰居節點當作它的伙伴，當來源節點傳送封包給無線存取點失敗時，伙伴就轉送同一份封包給無線存取點，這樣會比來源節點自己重送來的快，而且也可以將封包遺失的風險分散，使得重送的封包仍傳送失敗的機率降低。透過NS-2模擬工具評估我們所提出的方法，顯示吞吐量及封包遺失率都有明顯的改善，因此在多頻道無線網路使用這個協定可以提高整體網路的效能。

In an infrastructural wireless network, nodes communicate through an access point (AP). However, the signal quality between the AP and each node is dynamically changing in the wireless environment. When a node with low transmission capacity accesses the shared wireless channel, it takes longer transmission time than a node with high transmission capacity and may cause the decrease of overall throughput. In this thesis, we propose a relay-based cooperative MAC scheme in multi-channel wireless networks to address the throughput performance issue. The central idea is that nodes with high transmission capacity are allowed to relay data for nodes with low transmission capacity in a cooperative basis. The simulation results show that our proposed mechanism not only increases overall throughput but also reduces packet loss rate.

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