一個無線區域網路EDCA上支援媒體串流之無接縫交遞機制

Abstract

支援無線區域網路行動性的無接縫及快速交遞機制的部份研究中，均以交遞發生前先行偵測交遞對象為基礎，並已發展完整。「鄰近圖」(neighbor graph) 是提供偵測交遞對象資訊的方法中最常見的一種。但「鄰近圖」因為先天特性的一些缺點，至今都還沒被廣泛的應用。在這篇論文中，我們提出了所謂「不連續掃描」的機制來承襲「鄰近圖」的功能且排除其不實用的缺點。在「不連續掃描」的基礎上，我們更進一步提出了一些機制來幫助行動工作站在交遞前選擇合適的基地臺作為交遞對象，並用模型分析及模擬的方法來驗證這些機制的效能。「不連續掃描」最重要之疑慮可能在於對行動工作站的服務品質產生衝擊。然而，模擬結果顯示，對一個在無線區域網路EDCA上運作的媒體串流而言，「不連續掃描」造成的中斷將可以被控制在可接受的程度以內。

Seamless or fast handoff schemes to support mobility of IEEE 802.11 Wireless LANs have been well developed based on the assumption that a set of next-AP/AR candidates are available prior to a handoff. A neighbor graph is one of the major strategies used to provide such information among the related studies. However, neighbor graphs have not been widely applied yet due to its inherent drawbacks. In this thesis, a so-called “discrete scan” scheme is proposed to substitute the function of a neighbor graph without drawbacks. Moreover, several mechanisms based on discrete scan are presented to help a mobile node select a desired next AP to handoff to. The analytical model and simulation are elaborated to show performance of the approaches. Discrete scan may bring concerns on its impact to received QoS of the mobile node. However, the simulation results show that disruptions caused by discrete scan can be controlled within an acceptable value for a media streaming device working under EDCA over wireless LAN.