無線網路負載平衡改善機制之研究

A STUDY OF LOAD BALANCE FOR WIRELESS NETWORKS

廖志明(Chih-Ming Liao)

指導教授 ： 蔡佳勝

大同大學/電機資訊學院/資訊工程學系所/碩士(2011年)

摘要

WiFi與WiMAX的快速發展與佈建，使得都會區與辦公室的無線存取變的更加方便，伴隨而來的網路頻寬(Band Width)分配議題也就變得非常重要。由於存取點AP(Access Point)在規畫時都會適當規劃其架設的位置，以期待能夠發揮最佳的效能。然而移動節點MN(Mobile node)是活動的，常會因應各種需求而集中到某些區域。由於大部分移動節點的無線網卡(Wireless Adapter Card)會連結到訊號最強的存取點，如此會造成熱區(Hot Area)中特定存取點的壅塞，除了可能導致移動節點可以使用的頻寬降低外，甚至無法順利工作。
這篇論文主要是提供一種不需變動任何AP與協定且運行於MN端的方法，解決目前無線網路因移動節點分布不平均而造成的網路熱區問題，間接協助減少網路負載不平衡的問題。主要是利用由各存取點的頻寬使用狀態，各存取點上移動節點的連接數及移動節點的流量(throughput)決定是否須更換存取點，以取得更大頻寬的使用機會。 MN 主動尋求最佳的AP重新連線後，所涵蓋的網路負載因為頻寬分配更為平均，自然間接的達到負載平衡的目的。
最近發展迅速的WiMAX在Base Station間可以互相傳遞彼此的負載狀況與換手的相關資訊，新的802.16m可以容許Mobil Terminal 主動發起連線的需求 [1]，因此本研究也簡介WiFi與WiMAX的的差異。

關鍵字

hot area ； Load balance ； IEEE 802.11

並列摘要

According to the spread of wireless LAN, multiple access points (APs) will be much more likely to be available there for mobile nodes (MNs), which can roam from one AP to another by some rule. Consequently, following significant issue can arise in those cases: how to select an appropriate AP among available APs. In the existing architecture, the received signal strength is usually used to select an AP. However, such AP selection strategy causes the concentration of MNs to specific APs and MNs cannot use the resource of wireless LAN effectively.Hence, we proposed TRE (Throughput Re-Evaluate ) mechanism as the AP selection strategies, and showed that proposed strategies can achieve opportunity to use redundant wireless resources . Then, we here examine TRE mechanism by NS2 to prove that the efficiency can increase 6.3% to 7.9%. And we fully use the redundant resource.

並列關鍵字

hot area ； Load balance ； IEEE 802.11

參考文獻

[7] Shiann-Tsong Sheu and Chih-Chiang Wu, “Dynamic Load Balance Algorithm (DLBA) for IEEE 802.11 Wireless LAN”, Nov. 1999.

[1] WiMAX FORUM WHITE PAPER ,“WiMAX and the IEEE 802.16m Air Interface Standard “, Apr. 2010

[4] Maya Rodrig ,Charles Reis ,Ratul Mahajan ,David Wetherall ,John Zahorjan” Measurement-based Characterization of 802.11 in a Hotspot Setting “, Aug. 2005

[5] H.Velayos, V. Aleo and G. Karlsson, "Load balancing in overlapping wireless LAN Cells", June 2004.

[6] Ying –Hong Lo,”Mitigating Query Hotspot by Mobil Agents IN Wireless Sensor Network”, Aug.2009.