上行正交分頻多址系統中實虛部非協調與載波頻率偏移之同估測

Abstract

正交分頻多址近期已應用於許多無線通訊標準，但OFDM系統易受傳送端與接收端的設計不理想所影響，本篇論文著重於解決實虛部非協調以及載波頻率偏移的影響。實虛部非協調會產生鏡像干擾，載波頻率偏移則會破壞載波間的正交性，以上問題會造成載波間干擾以及用戶間干擾，因此必須對其估測與補償。 許多現有針對正交分頻多址系統之實虛部非協調估測方法都是針對接收端之實虛部非協調，針對傳送的估測則相對較少。本篇論文題出一個新的估測方法，估測對象為傳送、接收端之實虛部非協調，以及通道。我們提出的方法適用於任何領航符碼配置傳輸系統以及適用於大部分之載波分配方法，此外，此估測僅需使用一個OFDM符碼即可完成。我們提出的方法能用於估測頻率獨立與頻率相依之實虛部非協調，也能進一步估測載波頻率偏移。本論文各章節末附上各種情況下之估測結果之模擬圖。

Orthogonal Frequency Division Multiple Access (OFDMA) has already been widely adopted in many communication standards. However, the OFDM-based systems are sensitive to front-end non-idealities from the direct conversion transceiver. In this thesis, we focus on the in-phase and quadrature imbalance (IQI) and carrier frequency offset (CFO). The IQI leads to the image interference and the CFO destroys the orthogonality among the subcarriers. These effects will result in inter-carrier interference (ICI) and multiple-access interference (MAI). So the estimation and compensation are crucial for OFDMA systems. Most existing IQI estimation methods in the OFDMA systems are mainly focused on receiver (Rx) IQI. There are relatively few researches on Tx IQI. In this theses, we introduce a new joint Tx/Rx IQI and channel estimation method. Our proposed method can work for any pilot patterns and it can be applied to arbitrary carrier assignment scheme (CAS). Moreover, only one OFDM symbol is needed. We also extend the proposed method to pilot-based transmission where pilots and data are sent in one OFDM symbol. The joint estimation of CFO, IQI and channel is also considered. Both frequency independent (FI) and frequency dependent (FD) IQI are studied. Numerical simulations are carries out to show the performance in different scenarios.