IEEE 802.11a/g無線區域網路系統之合作式通訊

Abstract

分集(Diversity)是用來對抗衰落的技術，無論是時間、頻率及空間(Spatial)分集，傳送信號經由多個獨立的衰落通道到達接收機，透過接收機內部適當的組合(Combining)，可以獲得分集增益(Diversity Gain)。其中，空間或天線分集是比較常用的技術，因為它不需要增加傳輸時間或頻寬。但是有些情況，通訊終端(Terminal)會有硬體尺寸及成本的限制，而不能允許或有效的使用多根天線的設計。 合作分集(Cooperative Diversity)是另外一種可以實現空間分集以對抗衰落的技術，它可以讓一根天線的終端藉由網路內的其它一個或多個終端的合作而形成虛擬的陣列天線，因此可以獲得空間分集的效益。目前文獻中所見之合作式通訊大多是以理論的探討為主，比較少針對特定的系統做應用之評估。本論文的主要目的即是研究合作式通訊在IEEE802.11a/g系統中的應用並作效能之評估，結果顯示合作式的通訊可以有效的提高IEEE802.11a/g系統在衰落通道的性能表現。

Diversity is a well-known technology combating fading effects in wireless communications. Diversity, in time, frequency or space, can be obtained with signals transmited through independent fading channels, and received by some combining technique. Spatial or antenna diversity has the advantage that it does not have to increase the transmition time and bandwidth. However, in many case, the transmitter have limits on its phisical size or cost. As a result, multiple antennas are either not allowed, or the diversity gain is not significant. Cooperative diversity is a recently developed diversity technique. With the technique, a transmitter with only one antenna can have spatial diversity provided by the virtual antenna array, joined formed with other transmitters. In the literature, most works in cooperative communications focus on theoretic inverstigation. Few results are reported in the performance evaluation of real-world systems. In this thesis, we fill this gap by investigating the cooperative communications with IEEE 802.11a/g wireless LAN systems. Using well-knonw cooperative protocols, we conduct performance evaluation with extensive simulations. The results show that the performance of the wilress LAN system can be significantly enhanced through user cooperation.