臺灣博碩士論文加值系統

在IEEE 802.11協定中，資料訊號與控制訊號傳輸速率不同，因為資料訊號是以單點傳播 (unicast) 方式傳遞給單一節點，而控制訊號是以廣播方式 (broadcast) 讓較多的鄰近節點接收，兩種不同速率的訊號會產生不同的傳送距離，而不同傳輸距離會造成訊號涵蓋範圍不一致，通常控制訊號涵蓋範圍比資料訊號涵蓋範圍大4~6倍，而不一致的訊號涵蓋範圍會造成以下兩種現象：一、兩通訊節點間可能建立好交握 (handshake) 機制後，卻因為資料訊號傳輸距離較短而沒辦法進行資料傳輸。二、在控制訊號範圍內所有節點皆無法傳送訊息，但事實上資料訊號涵蓋範圍較小，在資料訊號範圍外控制訊號範圍內的節點仍可作資料傳輸卻設定為NAV (Network Allocation Vector)。為了提高傳輸節點個數，在我們的設計目標中，讓在資料訊號傳輸範圍外控制訊號傳輸範圍內的節點皆不被設定NAV，並且，為了讓控制訊號與資料訊號間彼此不會互相干擾，我們利用通道分割的方法，將通道分成多通道 (控制、資料與ACK通道)。除此之外，當通道分割後，不佳的頻寬配置將會影響效能，因此，我們提出了最佳化頻寬配置的方法，可以讓通道分割後的整體效能有效提升。為了驗證我們所提出的方法，在模擬中，我們將提出的方法與IEEE 802.11 DCF方法及其他學者提出的方法作效能、碰撞次數及封包平均等待時間比較，以不同的通訊對個數觀察效能、碰撞次數及封包平均等待時間的變化，我們的方法有效減少了約60~70%的碰撞次數，在整體效能上最少約有30~40%的提升，也有效降低封包平均等待時間，透過模擬分析，我們可以發現所提出的方法在效能、碰撞次數及封包平均等待時間有明顯的改善。

In IEEE 802.11, the transmission rate of the data signals is different from the transmission rate of control signals. The different transmission rate causes the different signals coverage. Usually the control signals coverage is 4 to 6 times bigger than data signals coverage. There are two problems occur in different signals coverage. One is the communication pair has finished handshaking but they can’t transmit data packet. Because of the data signals can’t reach the communication receiver nodes. The other is all the nodes in control signal coverage they can’t communicate with other nodes. In fact, the data signals coverage is smaller than control signals coverage. The nodes in control signals coverage but not in data signals coverage can communicate with other nodes. However, they set their status in NAV (Network Allocation Vector). Our purposed method is to increase the communicate nodes. We expect the nodes in control signals but not in data signals not to set their status in NAV, the control signals and data signals not interfere with each other. We separate the Channel into Multiple Channels (control channel, data channel and ACK channel). Furthermore, the bad bandwidth allocation strategy will decrease network throughput. We proposed the optimal bandwidth allocation strategy to increase network throughput. To estimate our method, we compare IEEE 802.11 DCF with ours in throughput and collision number. Our method increase 30 to 40 percent network throughput and decrease 60 to 70 percent collision number. According to our simulation results, our method increase network throughput and decrease collision number efficiently.

誌 謝 i
摘 要 ii
Abstract iii
目 錄 iv
圖目錄 vi
表目錄 vii
第一章 緒論 1
1.1 背景 1
1.2 研究動機 1
1.3 研究目的 2
第二章 相關研究 6
2.1 IEEE 802.11 DCF簡介 6
2.2 以速率選擇改善效能相關研究 7
2.3 以調整占用通道時間分配改善效能相關研究 7
2.4 以通道分割改善效能相關研究 8
第三章 提出的方法 9
3.1 分析涵蓋範圍的差異性 9
3.2 設計目標 12
3.3 提出的演算法 13
3.4 頻寬配置策略 16
3.4.1 不佳的頻寬配置 16
3.4.2 良好的頻寬配置 17
3.5 涵蓋範圍的影響 19
第四章 模擬結果與分析 22
4.1整體網路產能 23
4.2碰撞影響情形 25
4.3通訊對產生到封包開始傳送平均等待時間 26
第五章 結論 29
參考文獻 30
簡 歷 34

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