OFDM決策迴授等化系統設計與分析

Abstract

無線通道因為電磁波的反射、繞射等現象，會產生多重路徑干擾的衰減現象(multi-path fading effect)，因而造成系統效能降低、錯誤率提高等現象，所以在接收端都會使用等化器(equalizer)來補償通道效應並抑制干擾與雜訊。等化器會依架構與演算法而分類，其中以決策迴授等化器最能有效消除多路徑干擾且不會放大雜訊。 本篇論文主要的內容就是針對單載波系統(Single carrier system)中的決策性等化器構造，設計並推廣到正交分頻多工系統(OFDM system)，並且比較此架構與線性等化器架構的效能差異。此外，不同的等化系統受到通道估測誤差、通道編碼的影響也會不同，所以在這論文最後模擬的部分，我會把這些影響納入考慮並探討效能的差異。

Due to the reflection and diffraction of the EM wave, the wireless channels have the multipath fading effects. These influences reduce the system performance and the bit error rates of transmission raise. Therefore, we use the equalizer at the receiver to compensate the multipath channel influences and suppress the noise effect. The architecture and algorithms of equalizers are different, and in which, the decision feedback equalizer can remove the multipath interference effectively without enhancing the noise. In this thesis, we design the architecture and the algorithms of decision feedback equalizer which originally belonged to the single carrier system for OFDM system. We will compare the performances of our architecture and the linear equalizer. Furthermore, different equalization systems have different influences when they have channel estimation errors or with channel coding systems, so we will take these influences into account in the simulations which is in the end of this thesis.