在本論文中，我們首先介紹正交分頻多工 (orthogonal frequency division multiplexing, OFDM) 傳輸與調變技術的基本原理。其次，我們提出一種最大概似率 (maximum-likelihood, ML) 演算法作聯合頻率偏移與通道頻率響應估測 (joint frequency synchronization and channel estimation)於頻率選擇性通道 (frequency-selective channels)中的OFDM 系統。頻率偏移可能由載波頻率不同步及都卜勒頻譜延展(Doppler frequency spread) 兩者效應所引起。我們使用適應性梯度搜尋法 (adaptive gradient search) 進行頻率偏移的估測，而通道頻率響應 (channel frequency response) 將隨頻率偏移估測後獲得。然後在矯正頻率偏移後，我們再以合理假設運用最小均 (least squares)方法求得通道估測做一比較。我們提出的各種估測法在模擬結果中有十分準確的表現。估測法的模擬結果效能與理論分析之結果十分一致。 In this thesis, we first introduced the basic principle of the orthogonal frequency division multiplexing (OFDM) transmission and modulation technique. Second, we present a maximum-likelihood (ML) estimation algorithm for jointly estimate frequency offset and channel frequency response (CFR) for OFDM systems in frequency selective channels. Then, with proper approximations after frequency offset correction, a least squares approach is also used for channel estimation for comparison. The frequency offset may arise from both carrier frequency mismatch and Doppler spread effect. We use adaptive gradient search to estimate the frequency offset, the channel frequency response estimation is subsequently obtained. Simulation results of our proposed estimations show great estimation accuracies and are found in excellent agreements with theoretical predictions.
