前級非理想特性對正交分頻多工無線區域網路傳收機影響之研究

Abstract

無線區域網路IEEE 802.11a採用正交分頻多工(Orthogonal Frequency Division Multiplexing, OFDM)的技術，可以抵抗多重路徑(multipath)的效應，同時能提供高速傳輸，但須解決OFDM訊號具有高峰均值功率比(peak to average power ratio, PAPR)的問題。在本論文中，吾人評估使用編碼與攪亂子載波訊號相位的方式對降低OFDM訊號PAPR的效能與複雜度，同時尋求適於IEEE 802.11a規格之解決方案。另一方面，吾人將探討無線傳收機之非理想特性對OFDM系統的影響，諸如類比電路的不匹配造成I-Q不平衡(I-Q imbalance)的效應，振盪器的頻率飄移與相位雜訊引起的載波間干擾(ICI)，放大器造成之非線性失真等。吾人將介紹適用於IEEE 802.11a規格的架構與演算法，估測出訊號的失真並加以補償。整體而言，本論文將針對IEEE 802.11a之系統規格，謀求上述非理想特性的解決之道。

OFDM (Orthogonal Frequency Division Multiplexing) in wireless local area networks, such as IEEE 802.11a, is a promising technology for combating multipath propagation and maintaining high data rate transmission. A major drawback of OFDM is its high peak to average power ratio (PAPR). In this thesis, we first investigate coding and scrambling techniques for PAPR reduction and evaluate their performance and complexity. We then try to find suitable solutions for the IEEE 802.11a OFDM system. On the other hand, we will study the OFDM system under non-ideal front-end effects such as I-Q imbalance, carrier frequency offset, phase noise and power amplifier nonlinearity. In particular, we will introduce useful architectures and algorithms in order to compensate for the signals distortions due to non-idealities in the IEEE 802.11a system.