IEEE 802.11 多重跳躍無線網路上有向性天線媒介存取控制之研究

Abstract

藉由運用有向性天線在無線隨意網路上(Ad Hoc Networks)， 我們期望能得到空間再利用(spatial reuse)以及更長的傳輸距離(extended transmission range)所帶來的好處。 現存基於CSMA/CA(Carrier Sense Media Access with Collision Avoidance)的有向性天線媒介存取控制會帶來比運用全向性天線的媒介存取控制更多的hidden terminal問題。 而且因為有向性天線的特性，當運用有向性天線在無線隨意網路中會產生head of line blocking和deafness 的問題。 目前有一些基於TDMA(Time Division Multiple Access)的有向性天線媒介存取控制可以解決以上提到的問題，但必須要同步化網路中的每個無線裝置。 而在無限隨意網路中這樣分散且去中心化的環境下要同步化每個無線裝置是非常難辦到的。 在這篇碩士論文中，我們提出一個基於CSMA/CA的有向性天線媒介存取控制的通訊協定： DCS-MAC(Directional Carrier Sense Based Scheduling Media Access Control)。 DCS-MAC可以提供一個簡單、去中心化的分散式方法來達到一個鬆散同步化的效果。 藉由將傳輸控制封包及傳輸資料封包的時段分開，DCS-MAC可以解決大部份的hidden terminal 及 deafness問題。 而且DCS-MAC也藉於排程來解決head of line blocking 的問題。 由模擬的結果看出在簡單的環境中(較少的無線裝置,較少的資料流量負載)DCS-MAC雖然有比DMAC少的總資料輸出生產率，但卻能公平地分配每筆資料流的輸出生產率。 而在較複雜的情況下(更多的無線裝置,共多樣化的資料流負載)，DCS-MAC不管在總輸出生產率方面還是公平分配資料流輸出率方面都有比DMAC更好的表現。

By using directional antenna in ad hoc networks, we expect to get the benefits of spatial reuse and extended transmission range. Existing CSMA/CA based MAC protocols with directional antenna have more hidden terminal problem than which using omni-directional antenna. And since the characteristic of the directional antenna, they introduce deafness and head of line blocking problems which will degrade the network capacity when using directional antenna in ad hoc networks. Some TDMA based MAC could solve these problems. However it’s hard to synchronize nodes in a distributed and decentralized way. In this thesis, we propose a CSMA/CA based MAC protocol with directional antenna called DCS-MAC. DCS-MAC can synchronize nodes in ad hoc network loosely by a simple, distributed and decentralized way. By dividing the control packets and data packets transmission time period, DCS-MAC alleviates hidden terminal and deafness problems and takes head of line blocking problem into consideration. Simulation results show that in a simple environment (few mobile nodes, few traffic loads) DCS-MAC has lower aggregate throughput than DMAC but DCS-MAC make traffic load fair. In a more complex environment (more nodes, diverse traffic loads) DCS-MAC outperforms DMAC in aggregate throughput and fairness.