IEEE 802.11 MAC層通訊協定主要依靠兩種技術來避免干擾，載波感測和RTS/CTS handshake，一般的情形下，這兩種技術可以解決大部分的干擾，但是由於信號要能夠成功接收，其強度必須大於干擾信號許多倍，這導致了其他工作站可能在比傳送端與接收端的距離還遠的距離干擾接收，當傳送端與接收端的距離大於某一距離時，某些在RTS/CTS範圍外的工作站仍然可以干擾信號接收，因此RTS/CTS技術無法避免這種干擾，我們稱這種衝撞為大干擾範圍所造成的干擾。而如果將載波感測的範圍增至非常大，雖然能夠解決這個問題，但這受限於天線的硬體技術並且將導致網路的效能低落，因此亦不適宜解決這個問題，有許多的研究提出不同的MAC層通訊協定，其中許多方法能夠改善或解決干擾的問題，但是多半會造成能源的浪費，我們提出一個簡單的方法同時考慮干擾與能源消耗，模擬的結果證明我們的方法可以以節省的能源消耗解決大干擾範圍所造成的大部分干擾。

IEEE 802.11 MAC protocol uses two techniques to avoid interference – physical carrier sensing and RTS/CTS handshake (virtual carrier sensing). Ideally, these two techniques can solve most of interference problem. But in normal situation a host cannot receive packet successfully unless the power of receiving signal is much higher than that of interference signal. This fact leads that other host can interfere the reception in farther distance than the distance between the transmitter and the receiver. When the distance between the transmitter and the receiver is larger than certain value, some hosts that are out of the range covered by RTS/CTS packet may still interfere the receiver. This problem can be solved by using a very large physical carrier sensing range, which is limited by antenna and will reduce the network throughput. So it’s not suitable to avoid large interference problem. So far some schemes were proposed to solve or improve this problem, but most of them cause power waste at the same time. In this thesis, we will propose a scheme to look after both interference and power consumption. Simulation results verify that our scheme can solve most interference caused by large interference range with less power consumption.

1 Introduction.………………………………………………………………………1
1.1 Introduction………………………………………………………………1
1.2 Motivation…………………………………………………………………2
1.3 paper organization…………………………………………………………3
2 Related Work……………………………………………………………………4
2.1 TCP Instability Problem……………………………………………………5
2.2 TCP Unfairness Problem……………………………………………………6
2.3 RIBTMA (Receiver-Initiated Busy-Tone Multiple Access)………………8
2.4 Dual Busy Tone Multiple Access (DBTMA)………………………………9
2.5 Ad hoc Capacity……………………………………………………………10
3 Large Interference Area and CCR………………………………………………12
3.1 Large Interference Range Problem………………………………………12
3.1.1 Interference Area…………………………………………………13
3.1.2 Effective of IEEE 802.11 RTS/CTS handshake…………………14
3.1.3 Influence of Physical Carrier Sensing……………………………16
3.2 Conservative CTS Reply…………………………………………………17
4 Proposed Scheme…………………………………………………………………19
4.1 Power Control Interference Avoidance…………………………………19
4.1.1 Basic Idea…………………………………………………………19
4.1.2 Transmission Power………………………………………………20
4.1.3 Interference Area…………………………………………………22
4.1.4 Channel Split………………………………………………………23
4.2 Between CCR and Proposed Scheme………………………………………23
4.2.1 Ability to Combat Interference……………………………………23
4.2.2 Spatial Reuse………………………………………………………24
5 Simulation and Analysis……………………………………………………………26
5.1 Basic Simulation Setting…………………………………………………26
5.2 Simulation Result and Analysis……………………………………………27
5.2.1 Corruption Ratio……………………………………………………27
5.2.2 Throughput…………………………………………………………28
5.2.3 Power Consumption………………………………………………29
5.2.3 mobility……………………………………………………………31
6 Conclusion…………………………………………………………………………32
Reference……………………………………………………………………………34

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