無線區域網路IEEE 802.11(e) 中以競爭為基礎的吞吐量與服務品質分析改善之研究

Abstract

在現在這個資訊爆炸的時代，利用網路交換或是獲得所想要的資訊已經是非常普及了，其中，無線區域網路更節省了傳統有線網路所需要的硬體資源，更增加了移動的便利性，無異是在現有的思維中，提供了一種更快速方便的選擇。本篇論文便是建立在競爭無線區域網路資源的基礎上，針對現今的技術做進一步的分析與研究。本論文的第一個部分會提出一個新的802.11b DCF 的分析方法，藉由此分析法可以獲得在飽和時系統平均的吞吐量，而第二個部分則會提出一個建立在802.11b分散式協調功能(distributed coordination function，DCF)的機制上的改善方法，使得當通道較為壅塞時可以有效的減少碰撞發生的機會進而增進吞吐量，最後一個部分則會針對在802.11e加強型分散式通道存取(Enhanced Distribution Channel Access，EDCA）中的封包錯誤機率，研究不同等級間的吞吐量的改變與差異，並試圖改善錯誤機率產生的影響。

Both IEEE 802.11 and IEEE 802.11e define a mechanism apiece for stations to contend for channel resources without arrangement in advance. In this thesis we focus on the contention-based mechanisms and present three studies on them. In the first part, a novel model is proposed by considering the transmission probability of a specific station will increase or decrease after each time slot, and, based on this model, the throughput of 802.11 DCF is analyzed. Secondly, the 802.11 DCF mechanism is modified to improve its throughput in a hybrid environment by adding an extra part in front of every data packet using the basic access mechanism to protect it from collision with RTS packet(s). Finally, the contention window is adaptively adjusted in 802.11e EDCA, in order that the portion of QoS received by each service class under channel errors will remain the same as that under error-free channels.