動態選取基地台策略於IEEE 802.11無線網路

Abstract

在行動主機的普及化下，帶動整個無線網路的蓬勃發展，尤以熱點(Hot Spot)擴增最為明顯，設置密集度也逐漸增高，使我們隨時隨地皆可使用網際網路上的服務。而使用者在熱點是透過基地台上網來接收或傳送資料，此種無線網路傳輸資料方法，稱為基礎架構模式(Infrastructure mode)，使用者能夠獲得較佳的上網服務品質，不只在於基地台是否能夠提供較佳的頻寬，而且所選的頻道干擾也須要少，因此如何選擇一個提供較好的服務品質的基地台，便是本論文所要研究的問題。 在本篇論文中，我們分析影響網路負載的各項因素，提出且實作兩個動態選擇基地台的策略，一是由基地台廣播負載之策略，另一是探測訊框策略，利用訊框傳送與回覆時間來判斷網路的負載，使得不論在何種狀況，都能夠更精確的選擇服務品質較佳的基地台。此外，並將此兩種策略的實作透過測試來証明可以獲得較佳的效能。

Wireless communications have advanced rapidly in recent years. In the hot-spot areas, we have seen dense deployment of access points. Because of that we can get internet service everywhere. Users can connect to networks and send/receive easily. This transmission method is called infrastructure mode. A user will prefer to connect to an AP with higher bandwidth and less interference. This thesis is to address how a wireless station chooses an AP that can provide better service. In the thesis, we analyze the factors which affect the networks load. We will propose and implement two approaches to dynamically selecting access points based on our analysis. The first one is to broadcast load information by APs. The second one is to transmit detection frames to APs by stations so as to check the network loads of APs. The response time from APs will used to make the selection. The latter approach can select better APs under almost all conditions. Finally, we verify the effectiveness of our schemes by showing real experimental results.