在IEEE 802.11 的規格書當中，雖然在PHY層提供了多個頻道供資料傳輸使用，然而在MAC層卻只針對了單一頻道提出了媒體存取控制協定。由於使用多重頻道進行傳輸，可帶來比單一頻道較好的網路效能是有目共睹的。因此，本論文考量在IEEE 802.11 無線隨意網路中，針對多重頻道提出一簡單並有效率的多重頻道無線隨意網路媒體存取控制協定。此協定的目的在於有效的安排每一筆資料的傳送，使其能夠在適當的時間點與適當的頻道上進行資料傳送，並達到避免資料碰撞的目的進而提升整體的網路效能。基於此目的，本論文將會探討在多重頻道無線隨意網路環境中，將必須克服的種種問題，如隱藏節點問題、接收端節點消失問題與頻道使用率…等等。然而，基於硬體成本上的考量，無線網路通訊設備通常只配備了一個收發器。而若傳輸節點只配備單一收發器時，隱藏節點問題將以另一型態存在於多重頻道的無線隨意網路環境當中。因此本論文將針對在多重頻道無線隨意網路環境中，分析隱藏節點問題的存在型態。並將管線化處理的概念，帶入了多重頻道無線網路的資料傳輸當中，提出一類似管線化處理傳輸機制的多重頻道媒體存取控制協定 (π-Mc)，以避免因單一收發器而造成的多重頻道無線隨意網路下之隱藏節點問題。此外，本論文對頻道使用率亦有所琢磨，針對傳輸機制提出改善並有效地提升頻道使用率，進而將無線網路存取媒介資源的使用達到最佳化。由模擬實驗的結果可得知，本論文以管線概念所提出之 π-Mc多重頻道媒體存取控制協定，與IEEE 802.11 DCF機制相較之下，在網路傳輸效能的表現上將會隨著可以用頻道數的增加而有著顯著的改善。

Due to the consideration of hardware cost, the wireless adapter is only with single transceiver. However, if only single transceiver is available in the multichannel network, the hidden terminal problem will happen in the different way, and name as multichannel hidden terminal problem. Therefore, the paper analyzes this problem and proposes a pipeline-like multichannel MAC protocol (π-Mc) to avoid the multichannel hidden terminal problem. In addition, the paper also tries to increase the usage of the channel. Finally, π-Mc also compares with IEEE DCF and DCA. According to the simulation results, π-Mc can perform well in the network throughput and delay.

1	緒論	1
2	預備知識	18
2.1	多重頻道環境之隱藏節點問題	19
(1)節點與其他傳送對處於相同頻道上交換控制封包	19
(2)節點與傳送對處於不同頻道上交換控制封包	20
2.2	符號定義與假設	22
3	管線化之多重頻道媒體存取控制協定	23
3.1	基礎概念	24
3.2	各頻道停留之時間	29
3.3	避免碰撞與頻寬浪費	31
3.4	π-Mc Extension	35
4	模擬	40
5	結論	45
6	參考文獻	47

圖一.	IEEE 802.11a於北美地區可供使用的12個不重疊頻道之示意圖。	2
圖二.	IEEE 802.11b的頻譜遮罩	3
圖三.	IEEE 802.11b於北美地區可供使用的3個不重疊頻道之示意圖。	3
圖四.	假設網路上有兩個頻道可供使用，其分別為 C0與 C1。假設節點A與其鄰近節點C、F同樣處於C0頻道。若節點C與F同時交換CTS封包，則在節點A上將發生碰撞。因此節點A將無法獲知在接下來時段節點C與F頻道使用的情形為何，並且選擇與節點C、F相同的頻道進行資料的傳輸。	19
圖五.	假設網路上有兩個頻道可供使用，其分別為C0與 C1。假設節點A與其鄰近節點C、F處於不同頻道(節點A處於C1而鄰近節點C與F則座落於 C0)，因此節點A並不知曉接下來節點C與F將處於哪一頻道。若之後節點A選擇到與節點C、F相同頻道傳輸資料，則碰撞將會發生。	20
圖六.	管線技術之多重頻道媒體存取控制協定示意圖	25
圖七.	傳送時間排程適當之情況	31
圖八.	傳送時間排程不當產生頻寬浪費之情形	33
圖九.	傳送時間排程不當產生碰撞之情形	34
圖十.	考慮切割最大封包大小示意圖	35
圖十一.	多對傳輸對根據最大封包大小切割傳輸時間	36
圖十二.	單筆資料傳輸模式示意圖	37
圖十三.	π-Mc Extension免碰撞示意圖	38
圖十四.	多筆資料傳輸模式示意圖	39
圖十五.	封包長度為1500 Octets時，封包產生率與網路傳輸效能的關係	42
圖十六.	封包長度為2312 Octets時，封包產生率與網路傳輸效能的關係	43
圖十七.	封包長度為512及1024 Octets時，封包產生率與網路傳輸效能的關係	44


表一.符號介紹	22
表二.實驗的模擬參數	40

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