多階無線區域網路效能研究

On the Performance of Multihop Wireless LAN

王冠仁(Guan-Ren Wang)

指導教授 ： 謝忠健

大同大學/電機資訊學院/資訊工程學系所/碩士(2004年)

摘要

隨著網際網路的蓬勃發展，資訊與通訊技術的快速進步，無線區域網路
技術成為現今熱門的焦點之一。
相較於有線區域網路，無線區域網路具有如下優點：
不需施工佈線與線路規劃，可節省成本與時間
可與既存之有線網路資源結合
資源分享更加便利
即便是行動中，仍可隨時隨地使用
故具備了無線繫絆，高移動性的特點。
IEEE 802.11是美國電子電機學會所制定的無線區域網路標準，採用的存取機制為分散協調功能(DCF)即載波感測多重存取/碰撞避免(CSMA/CA)。
而其中無線網路架構分為隨意型網路(Ad hoc Network)與
具基礎架構網路(Infrastructure Network)兩種。
雖然IEEE 802.11使用了DCF的機制，以減少競爭時碰撞可能發生的機會。
但在行動節點彼此競爭傳送權的過程中，還是極有可能會引起隱藏節點(hidden node)或暴露節點(exposed node)的問題。
進而發生碰撞或降低利用率，造成整體傳輸效能的下降。
而且機制中使用的返回(backoff)方式亦有傳輸媒介分配不公平的現象。
本研究針對隨意型網路環境下現有IEEE 802.11無線區域網路標準的缺失進行探討改善，
進而避免造成無線傳輸的效能不彰，以達到較佳的頻寬利用率。

關鍵字

無線區域網路

並列摘要

With the developing of Internet and the rapidly advance of information and communication technology, wireless LAN technology has become the popular topic nowadays. Comparing with wired LAN, wireless LAN has the following advantages:
Without wiring construction and planning circuit, cost and time can be reduced.
Integrated with already existing wired LAN resources.
Resources sharing gets more convenient.
Even moving, resources can be employed anytime or anywhere.
It possesses the characteristics: no wiring hassle and high mobility.
IEEE 802.11 is the wireless LAN standard drawn by American Institute of Electrical and Electronic Engineers, and using the Distributed Coordination Function (DCF) aka Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA) as the access mechanism. The topologies which wireless LAN supports are ad hoc network and infrastructure network.
Although IEEE 802.11 uses DCF as MAC protocol to reduce the probability of collision while contention. However during the contention among mobile nodes, it has the strong probability causing the hidden node problem or exposed node problem. The former will suffer collisions and the latter will reduce utility rate. The random backoff scheme may also cause the unfairness of medium access though.
This study focuses on improving the weaknesses of the wireless LAN standard IEEE 802.11 working in ad hoc network and avoiding the low efficiency to achieve the enhanced utility rate of bandwidth.

並列關鍵字

Wireless LAN

參考文獻

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