臺灣博碩士論文加值系統

在無線隨意區域網路（wireless ad hoc networks）中，媒體存取層（medium access control；MAC）的設計與實體層的能力充分影響著系統的效能與容量。本論文提出一以分碼多工（code division multiple access；CDMA）為基礎的無線隨意區域網路系統，並在媒體存取層設計一簡單易實現的方法來控制多重存取干擾（multiple access interference；MAI），並設計一組多重通道的競爭方法來增加系統的效能。

我們試著修改IEEE 802.11分散式協調功能（distributed coordination function；DCF）中的後退演算法；在網路可使用的通道數愈多時，各節點（node）倒數計數器遞減的速度愈快，以縮短各節點隨機倒數（random backoff）所花的時間。並提出通道調節（channel regulation）與機率傳送（p-persistent）的機制來降低碰撞發生的機率；我們在最大通道數之下，設定通道使用的臨界值，當網路上正在傳輸的節點數，尚未到達設定的臨界值時，競爭到通道使用權的節點便可立刻傳送封包。當網路上正在傳輸的節點數，達到設定的臨界值時，競爭到通道使用權的節點，便只有一定機率可以將封包傳送出去。

最後，將我們所提的方法與傳統IEEE802.11 DCF競爭機制相比較，從模擬結果顯示，在多通道競爭的環境下，我們所提的方法有效的克服因多重存取干擾導致整體效能下降的問題，使隨意網路的整體效能與容量提升了數倍。

In wireless ad hoc networks, the design of medium access control (MAC) layer and the ability of physical layer have full influence to system efficiency and capacity. This paper provides a new wireless ad hoc networks based on code division multiple access (CDMA), and designs a way in the MAC layer which one will be easy to realize to control the multiple access interference (MAI), and designs a competition way of multi-channels to increase the system efficiency.

We try to revise the backoff algorithm under the IEEE 802.11 distributed coordination function (DCF); when there are more channels available to networks, the backoff counter decreases progressively speed is quicker, which could reduces the time each node spends. And we propose channel regulation and p-persistent mechanism; we establish the marginal value which the channel uses under the maximum number of channels. When the number of nodes transmitting on the network does not achieve the designed marginal value, the node succeeded in channel competition could transmit packet right away. When the number of nodes transmitting on the network arrival the designed marginal value, the node succeeded in channel competition could transmit packet with certain probability.

Finally, compared the method we propose with the traditional IEEE 802.11 DCF competition mechanism, demonstrated from the result of simulation, under the multi-channel competition environment, the method which we raise effective overcomes the problem caused by the multiple access interference which makes the overall performance drop, and promoted the overall efficiency and capacity of wireless ad hoc network several fold.

中文摘要……………...…………………………...........…......iv
英文摘要 ……………...…………………………...........….......v
圖表索引 ……………...…………………………...........…......ix

第一章 緒論 ……………………………………………….……...…..1
1.1 無線網路概述….……...………………………………………….1
1.2 研究動機……………………………………….………..……….. 3
1.3 章節概要…..……..……………………………….……..….….…5
第二章 IEEE 802.11與CDMA介紹………….…...............…6
2.1 IEEE 802.11無線區域網路…....………….…..…..….…..………6
2.1.1 IEEE802.11網路特性…………..……………...…………..6
2.1.2 IEEE802.11網路硬體架構…..……………………….……7
2.1.3 IEEE802.11DCF機制…...………………….…….…...…..10
2.1.4 隨意網路同步機制…......………………….…….…...…..12

2.2 分碼多重存取技術（CDMA）………………….….....………...13
2.2.1 CDMA起源及發展…...……...……………………….…..13
2.2.2 CDMA原理…..……………...……………………….…...14
2.2.3以傳輸為基礎（transmitter-based）的CDMA無線網路…………………………………………………………..15

第三章 系統架構………………… ……...……………….…...…16
3.1 網路基本架構...………………...…………………….…………16
3.2 實體層硬體架構.…...…….………………………...…..….…… 18
3.3 位元錯誤率對通道數之影響………………………...….……...21

3.4 系統演算法….....…...…….………………………...…..….…… 22
3.4.1提出的後退演算法……….……….……...………….……22
3.4.2提出的碰撞避免機制...….……..……………………....…23

3.5 演算法詳述….....…...…….……………………..….…..….…… 24
3.5.1 演算法實例……..…...……...……………………….……29

第四章 系統模擬與分析 …………...…………………………….31
4.1 效能評估項目….…...………….………………….……………. 31
4.1.1傳輸效能（throughput）………….……...………….……31
4.1.2平均傳輸延遲（average delay）....….……..………….…31
4.1.3封包平均碰撞次數(average collision times)….……….…31

4.2 模擬架構及參數………………………………...……………... 33
4.3 結果分析與比較 ………………………………...……………... 35
4.3.1最大通道數為11...…..…..…..….………...………….……35
4.3.2最大通道數為17...…..…..…..….………...………….……39
4.3.3最大通道數為41...…..…..…..….………...………….……42

第五章 結論 ……………………………………..………...………...47
參考文獻 …………………………………………………..……….…48

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