在無線隨意網路環境下一個具有功率控制的方向性媒體存取控制協定

Abstract

近幾年來方向性天線應用在隨意網路(ad hoc network)是很熱門的研究議題，因為方向性(Directional)天線比全方向性(Omni-Directional)天線提供了更多的優勢，除了提升空間的使用率之外，還可以減少co-channel干擾的情形、增加傳送的距離以及節省傳送所需的電力。不過，為了充分利用方向性天線的好處，必須重新設計一個MAC協定，所以許多使用方向性天線的MAC協定相繼被提出，其中又以D-MAC[3] 最受到重視。另外，透過控制功率(Power Control)的方式與方向性天線皆可以有效提升空間使用率。 在這篇論文中，我們先針對D-MAC所提的Scheme 1與Scheme 2來做分析，我們發現Scheme 1提升了空間的使用率，但是會產生一些碰撞情形，而Scheme 2減少了碰撞的發生，可是還是存在Deafness以及Collision的問題，也因此降低空間的使用率。於是我們提出了一個改進D-MAC Scheme 2的新協定，叫做F-DMAC。這一個方法提高了空間使用率並且減少碰撞的發生。接著我們將控制傳輸功率的方式使用在F-DMAC中，提出了另一個改進的新協定，叫做PCF-DMAC。PCF-DMAC結合了控制傳輸功率與方向性天線的優點，有效的降低碰撞情形以及提升空間使用率。使用J-Sim模擬實驗後，F-DMAC在Multi-hop、Mesh的環境下，網路輸出都表現的比IEEE 802.11以及D-MAC Scheme 2還要好，而PCF-DMAC在Multi-pair的情況下則比IEEE 802.11、D-MAC Scheme 2以及F-DMAC都還要好。

Applying directional antenna to ad hoc network has been a hot research topic, because directional antenna has more advantages than omni-directional antenna, such as increase spatial reuse rate, diminution of co-channel interference, acceleration transmission distance, and saving transmission power. However, in order to fully utilize the benefit of directional antenna, MAC protocol has to be redesign, and among those directional antenna MAC protocol are successively proposed, D-MAC gets the high consideration. Except for directional antenna, spatial reuse rate can also be improved through controlling transmission power, so that studying how to apply controlling transmission power to directional antenna is glamour as well. In this thesis, we analyzed Scheme 1 and Scheme 2 the D-MAC mentioned, and discovered Scheme 1 increase in the spatial reuse rate, but there are some collision happened. For Scheme 2, nevertheless, even though the collision is diminished, it decreases the spatial reuse rate. Upon this, we proposed a new protocol named F-DMAC for meliorating D-MAC. This method not only enhances the spatial reuse rate but also reduces collision chance. After F-DMAC, we addressed the other advanced protocol, PCF-DMAC, applying controlling transmission power to F-DMAC. PCF-DMAC combines the advantages of controlling transmission power and directional antenna, which decrease the collision and raise the spatial reuse rage.