結合時域和頻域載波頻率估測法以改善正交分頻多工系統之載波間干擾

Joint Time-Frequency Domain Carrier Frequency Offset Estimation to Cancel Inter-Carrier Interference in OFDM Systems

黃信嘉(Xin-jia Huang)

指導教授 ： 曾德樟

國立臺北科技大學/機電學院/電腦與通訊研究所/碩士(2012年)

摘要

本論文針對正交分頻多工系統(OFDM)因載波頻率偏移(CFO)造成的子載波間干擾(ICI)提出分析與改善。正交分頻多工系統是具有高頻譜效率的調變技術，但對頻率同步錯誤非常敏感，只要些許載波頻率偏差，就會因子載波間的正交性(Orthogonality)喪失，而產生嚴重的載波間干擾。故本文針對接收端本地振盪器頻率不同步的狀況所造成的頻率偏移進行討論並提出改善方法。
本論文提出利用領航資料(Pilot Data)於LMS-like演算法在時域對載波頻率偏移做初步的收斂，並結合遞迴利用領航資料於最大概似估測法(MLE)結合自我干擾消除演算法(ISC)於頻域做載波頻率偏移估測，以期在相同的頻寬效益及增加些許計算複雜度的情況下，達到系統效能的改善。由電腦模擬結果顯示，本論文所提方法不僅能增加載波頻率偏移量的估測範圍，系統效能亦有明顯的改善。

關鍵字

正交分頻多工系統 ； 載波頻率偏移 ； 最大概似估測法 ； 自我干擾消除法 ； LMS-like

並列摘要

This thesis is mainly to analyze the inter-carrier interference (ICI) that induced by carrier frequency offset (CFO), and to improve it. The OFDM is a modulation technique with high bandwidth efficiency. It provides high data rates with limited bandwidth. However, one of the drawbacks is sensitivity to frequency synchronization errors. With slight CFO, the orthogonality among subcarriers will be destroyed, which in turn causes the ICI and degrades the bit error rate (BER) performance severely. Thus, we research into the solution for the CFO induced by imperfection of local oscillator frequency at the receiver side.
In this thesis we propose a new carrier frequency offset estimation method, which combines the Pilot LMS-like algorithm with the Iterative Pilot MLE-ISC algorithm to estimate the CFO by using the pilot data, to improve the system performance. Both the Pilot LMS-like algorithm and the Iterative Pilot MLE-ISC algorithm are performed in the time domain and the frequency domain, respectively. Under the same bandwidth efficiency, the proposed method can improve the system performance with increasing a little complexity. Simulation results also show that the proposed method can not only extend the estimation range of the CFO, but also increase the system performance.

並列關鍵字

OFDM ； Carrier Frequency Offset (CFO) ； Maximum Likelihood Estimation (MLE) ； ICI Self-cancellation (ISC) ； LMS-like

參考文獻

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