以子載波干擾相消法降低正交分頻多工系統受頻率擾動影響之研究

Abstract

為了減低正交分頻多工系統對頻率擾動的敏感度，我們使用子載波干擾相消法來達成這個目的。首先，我們分析了載波頻率漂移和相位雜訊對正交分頻多工系統的影響。在分析中可以發現這兩個非理想的效應都會造成子載波間干擾而影響系統整體效能。針對這個問題，我們分析並模擬了三種子載波間干擾相消法在存在載波頻率漂移或相位雜訊環境下的載波對雜訊比。這三種方法包括了：資料轉換法、資料共軛法和改良式資料共軛法。分析和模擬的結果可以發現，改良式資料共軛法除了改善了資料轉換法較高的峰值對平均功率比問題，同時也改進了資料共軛法的載波對雜訊比低落問題。另外，為了進一步改善子載波間干擾相消法頻譜效率較低的問題，我們提出了多重碼率子載波間干擾相消法。在分析和模擬中可以發現，當環境具有載波頻率漂移或相位雜訊下，只要能多提供一些傳輸能量，多重碼率子載波間干擾相消法便可有效地達到較高的頻譜效率。

In this thesis, the carrier frequency offset and phase noise effects in OFDM systems are analyzed. These non-ideal effects induce inter-carrier interference (ICI) which may deteriorate system’s performance. The ICI self-cancellation schemes, including data-conversion, data-conjugate, and our modified data-conjugate methods are analyzed and simulated. The theoretical derivation and simulation results show that our modified data-conjugate method shares the lower PAPR that data-conjugate method has and yet has CIR improvements. Moreover, to increase the bandwidth efficiency of normal ICI self-cancellation schemes, a multi-rate ICI self-cancellation scheme is also proposed. The simulations are done in both phase noise and carrier frequency offset environments. Results show that with some extra power, the multi-rate ICI self-cancellation scheme can be effectively used in OFDM systems to combat phase noise problems.