【正文】 蘭州交通大學(xué)畢業(yè)設(shè)計（論文） I 摘要 作為一種特殊的多載波調(diào)制技術(shù) ，正交頻分復(fù)用（ OFDM， Orthogonal Frequency Division Multiplexing）因其高頻譜利用率、高數(shù)據(jù)傳輸速率以及良好的抗多徑干擾性能，廣泛地應(yīng)用于數(shù)字音視頻廣播、無線局域網(wǎng)等高速數(shù)據(jù)傳輸系統(tǒng)中。 OFDM 通信系統(tǒng)具備所有這些優(yōu)勢的前提是收發(fā)兩端子載波均要保持良好的正交性，然而，在實際應(yīng)用中，晶振的非理想因素以及移動通信中多徑信道產(chǎn)生的多普勒頻移將會造成OFDM 系統(tǒng)發(fā)射機(jī)與接收機(jī)載波中心頻率的偏移 （ CFO， Carrier Frequency Offset） ， 而這將嚴(yán)重破壞子載波之間的正交性，因此 OFDM 系統(tǒng)接收機(jī)必須對載波頻偏加以估計并對接收信號進(jìn)行相應(yīng)補(bǔ)償以保證解調(diào)數(shù)據(jù)的準(zhǔn)確性。通常，將這一操作稱為載波頻率同步，也可簡稱為頻偏估計。由于 OFDM系統(tǒng)對 CFO非常敏感，微小的 CFO就能造成系統(tǒng)誤碼性能的大幅下降，因此，頻率同步技術(shù)是 OFDM 系統(tǒng)的關(guān)鍵技術(shù)之一。 本論文首先回顧了 OFDM 技術(shù)發(fā)展的歷史，然后從基本的 OFDM 系統(tǒng)的原理出發(fā)，闡述了 OFDM 系統(tǒng)中的同步問題。接著詳細(xì)闡述了定時同步偏差和載波頻率偏差對系統(tǒng)性能的影響。最后，對 現(xiàn)有的頻率 同步技術(shù) （ 即 ， 盲同步算法和非盲同步算法 ）進(jìn)行了介紹且重點介紹了三種具有代表性的載波頻偏估計算法：子載波間干擾（ ICI，Intercarrier interference）自消除方法，高階子載波間干擾（ ICI）自消除方法和頻率偏移盲估計方法，并通過仿真比較分析了它們在加性高斯白噪聲信道和頻率選擇性信道下的估計性能。 關(guān)鍵詞： 正交頻分復(fù)用；載波頻率偏移；子載波間干擾；盲載波頻偏估計；自消除 蘭州交通大學(xué)畢業(yè)設(shè)計（論文） II ABSTRACT As a special multicarrier modulation technique OFDM（ Orthogonal Frequency Division Multiplexing） has been widely used in data transmission systems such as Digital Video/Audio Broadcasting systems and wireless LAN systems, due to its high spectral efficiency, high data rate, and excellent performance to bat with multipath interference. It is the orthogonality between the subcarriers in OFDM systems that guarantees all those strengths mentioned above. However， the carrier frequency offset, caused by the nonideal factors of the oscillators and the Doppler Shift introduced by the multipath channel, will destroy the orthogonality between the subcarriers. In order to get a better performance, the receiver should estimate the carrier frequency offset and then pensate the received signal, which is usually called as carrier frequency synchronization or frequency offset estimation for short. OFDM systems are very sensitive to carrier frequency offset, that is to say, a small frequency shift could degrade the system performance dramatically. Therefore, frequency synchronization technique has bee one of the key techniques of OFDM systems. Firstly, this dissertation reviews the history of the development of OFDM technique. According to the basic OFDM theory, this dissertation describes synchronization of OFDM systems. Then, describes the effect of the timing offset and frequency offset to the system in detail. Finally, the frequency synchronization of existing technologies（ . the blind algorithm and the nonblind algorithm） is introduced and this dissertation focus on the three typical carrier frequency offset estimation algorithm: Intercarrier Interference SelfCancellation, Highorder Intercarrier Interference SelfCancellation and Blind Deterministic Frequency Offset Estimation Method. Performances under AWGN channel and frequencyselective channel are analyzed and pared by simulation. Keywords: Orthogonal Frequency Division Multiplexing（ OFDM） 。 Carrier Frequency Offset。 Intercarriers Interference。 Blind Carrier Frequency Offset Estimation。 Selfcancellatio蘭州交通大學(xué)畢業(yè)設(shè)計（論文） III 目錄 摘要 ............................................................................................................................................. I ABSTRACT ...............................................................................................................................II 1 緒論 ...................................................................................................................................... 1 引言 ............................................................................................................................... 1 OFDM 技術(shù)的歷史及發(fā)展現(xiàn)狀 ................................................................................... 1 OFDM 技術(shù)的優(yōu)缺點 ................................................................................................... 2 OFDM 技術(shù)的優(yōu)點 ............................................................................................. 2 OFDM 技術(shù)的缺點 ............................................................................................. 3 論文的主要工作和章節(jié)安排 ....................................................................................... 4 2 OFDM 系統(tǒng)基礎(chǔ) .................................................................................................................. 5 無線信道特征 ............................................................................................................... 5 多徑信道模型和信道參數(shù) ................................................................................ 6 多徑時延擴(kuò)展衰落效應(yīng) .................................................................................... 7 Doppler 擴(kuò)展衰落效應(yīng) ....................................................................................... 9 正交頻分復(fù)用（ OFDM）技術(shù)與頻分復(fù)用（ FDM）技術(shù)的比較 .......................... 9 OFDM 系統(tǒng)的分類 ..................................................................................................... 10 CPOFDM 系統(tǒng) ............................................................................................... 10 ZPOFDM 系統(tǒng) ................................................................................................. 11 基于 IFFT/FFT 的 OFDM 系統(tǒng)原理 ......................................................................... 11 OFDM 的基本原理 ........................................................................................... 11 基于 IFFT/FFT 的 OFDM 系統(tǒng) ...................................................................... 14 串 /并變換 ......................................................................................................... 14 信號映射 .......................................................................................................... 15 利用 IFFT/FFT 實現(xiàn) OFDM 符號的調(diào)制與解調(diào) .......................................... 15 保護(hù)間隔 .......................................................................................................... 16 循環(huán)前綴 .......................................................................................................... 17 OFDM 系統(tǒng)的關(guān)鍵技術(shù) ....