【正文】 參考文獻(xiàn)[1], data transmission techniques for linear systems[J].., 1957:656661.[2] fading limitations of the Kathrynu modem and some system design considerations[J].IEEE .,1965,13(9):320333.[3], transmission by frequency division multiplexing using the discrete fourier transform[J].IEEE Comm., COM19(5):628634.[4],. Frequency domain data transmission using reduced putational plexity algorithms[J]. Speech Processing , Signal, Denver,1980:964967.[5] COFDMBased system for terrestrial television[J]. International Broadcasting Convention, Conference Publication , IEEE，1996:120126[6] 協(xié)議[J].山東大學(xué)學(xué)報(bào)(工學(xué)版),2003, 33(2): 168171.[7] and . Frequency synchronization algorithms for OFDM systems for munication over frequencyselective fading channels[J]. Proc. IEEE Vehicle Technology Conf. Stockholm, Sweden, 1994,3(3): 16551659.[8] and . Robust frequency and timing synchronization for OFDM[J]. IEEE Trans. Commun, 1997, 45(12):16131621.[9]Yun Hee Kim, Iickho Song, Seokho Yoon, So Ryoung Park. An efficient frequency offset estimation for OFDM systems and its performance characteristics [J]. IEEE Transactions on Vehicular Technology, 2001, 50(5):13071312.[10]Baoguo Yang,Roger ,and Zhigang Cao,Timing recovery for OFDM transmission[J].IEEE Journal on Selected Areas in Communications, 2000,8(11):22782291. [11]HuiLiu, highefficiency carrier estimator for OFDM munications [J]. IEEE Trans,1998,2(4):104106.[12]Tureli U, Liu H, Zoltowski M. OFDM blind carrier offset estimation: ESPRIT [J]. IEEE Trans. Commun., 2000, 48(9): 14591461.[13]Rohit Negi, John Cioffi M. Blind OFDM symbol synchronization in ISI channels [J]. IEEE Trans. Communications, 2002, 50(9): 15251534.[14]Ivan Bradaric, Athina P. Petropulu. Blind estimation of the carrier frequency offset in OFDM systems [J]. IEEE Workshop on Signal Processing, 2003:590594.[15]Vanbe Beek J, Sandell M, Burleson P O. ML estimation of time and frequency offset in OFDM systems [J]. IEEE Trans. Signal Processing, 1997, 45(7): 18001805.[16]YangSeok Choi, Peter J. Voltz, and Frank A. Cassara. ML estimation of carrier frequency offset for multicarrier signals in Rayleigh fading channels [J]. IEEE Transactions on vehicular technology, 2001, 50(2): 644651.[17]JiaChin Lin. MaximumLikelihood frame timing instant and frequency offset estimation for OFDM munication over a fast rayleighfading channel[J].IEEE, 2003:10491061.[18]Tiejun lv, Hua Li, and Jie estimation of symbol timing and carrier frequency offset of OFDM signals over fast timevarying multipath channels [J]. IEEE Trans. Circuits Signal Processing, 2005,53(12): 45264535.[19]Jungwon Lee, HuiLing Lou, Dimitris Toumpakaris, John M. Cioffi. Effect of carrier frequency offset on OFDM systems for multipath fading channels [J]. IEEE Communications Society,2005,5(4):32713275.[20] 系統(tǒng)中一種改進(jìn)的基于循環(huán)前綴的同步迭代算法[J].吉林大學(xué)學(xué)報(bào),2007,37(1):177181.[21]Chunlin Yan, Shaoqian Li, Youxi Tang, Xiao Luo, and Jiayi Fang. A novel frequency offset estimation method for OFDM systems with large estimation range [J]. IEEE T ransactions On Broadcasting,2..6,52(1):5861.[22]Bo Ai, Zhixing Y ang, Changyong Pan, Jianhua Ge,Yong Wang, the synchronization techniques for wireless OFDM systems [J]. IEEE Transactions On Broadcasting, 2006,52(2):236244. [23]Tiejun Lv, Jie Chen. ML estimation of timing and frequency offset using multiple OFDM symbols in OFDM systems [J]. IEEE, 2003, 4(4):22802284.[24]ChienChih Chen, JungShan Lin. Iterative ML estimation for frequency offset and time synchronization in OFDM systems [J]. IEEE Processing, 2004:2123.[25]Crussiere, M. Baudais, . iterative time and frequency synchronization scheme for MCCDMA systems over power line channels [J].IEEE Transactions On Broadcasting ,2004,1(3):315319.[26]Xiaojin Li,Yu Zheng,Zongsheng low plexity sign ML detector for symbol and frequency synchronization of OFDM systems [J]. IEEE 2006, 52(2):317320.[27]Huarong Zheng, Jue Tang and Bo Shen, Lowplexity joint synchronization of symbol timing and carrier frequency for OFDM systems [J]. IEEE Trans. Consumer. Electronics, 2005, 51(3):783789.[28]M. H. Hsieh,C. H. Weimar lowplexity frame synchronization and frequency offset pensation scheme for systems over fading channels [J].IEEE Trans. Vehicular. Technol., 1999, 48(5):254275.[29]A Peled, . Frequency domain data transmission using reduced Computational plexity algorithms [J]. Speech Processing, Signal, Denver, 1980:964967.[30] 關(guān)鍵技術(shù)與應(yīng)用[M].北京:：2529.[31]王文博， OFDM 技術(shù)[M].北京:: 35.[32]P. Chow, J. Cioffi, J. practical discrete multitone transceiver loading algorithm for data transmission over spectrally shaped channels [J]. IEEE 。 在實(shí)驗(yàn)室工作及撰寫論文期間，賈雄雄、張前鋒等同學(xué)對我論文中一些研究工作給予了熱情幫助，總能在與他們的探討中，獲得很多寶貴的靈感。在此表示由衷的感謝。他平易近人，從治學(xué)到為人，都讓我受益匪淺，無不潛移默化地影響我的人生。 由于受到時(shí)間和本人學(xué)習(xí)水平的限制，本課題的研究存在一些缺陷，在論文中難免存在一些不妥之處，敬請各位老師批評指正。 本文只是對算法進(jìn)行了研究，仿真的信道環(huán)境比較簡單，與實(shí)際應(yīng)用系統(tǒng)還有一定的距離。 本文的研究還有許多需要完善改進(jìn)的地方，這也將是我們以后研究中主要努力的方向，包括：對基于訓(xùn)練序列的同步算法和基于循環(huán)前綴的 ML 同步算法分析地不夠全面，比如沒有考慮捕獲時(shí)間和復(fù)雜度等問題。通過理論分析等方法研究了一些主要的同步算法原理和性能。研究了 OFDM 系統(tǒng)的原理,并對系統(tǒng)性能的優(yōu)缺點(diǎn)和關(guān)鍵技術(shù)進(jìn)行了歸納。本文主要研究OFDM 系統(tǒng)中的同步問題。 總結(jié)與展望 全文總結(jié)在無線通信系統(tǒng)中，OFDM 技術(shù)以其頻譜利用率高、抗多徑和脈沖噪聲、成本低廉等優(yōu)點(diǎn)，得到無線通信專家的廣泛關(guān)注， 并成為下一代移動(dòng)通信最具競爭力的關(guān)鍵傳輸技術(shù)之一。該算法還是成為了基于循環(huán)前綴的OFDM同步算法的典型算法模型，此后的很多學(xué)者在此基礎(chǔ)上提出了一系列的改進(jìn)算法，太大提高了同步的性能。()，對于超出這個(gè)范圍的頻偏，則無法實(shí)現(xiàn)有效的估計(jì)，所以該方法只適用于對小數(shù)頻偏的估計(jì)。： 接著，仿真系統(tǒng)采用256個(gè)子載波，循環(huán)前綴的長度為20個(gè)樣點(diǎn)，各路子載波采用QPSK調(diào)制方式。圖中確定符號定時(shí)位置的示意圖，當(dāng)其取得最大值的位置即為所要找的定時(shí)同步點(diǎn)，曲線都有較明顯的峰值。 ML算法仿真估計(jì)以下為Matlab仿真工具，： OFDM系統(tǒng)的仿真參數(shù)表參數(shù)名稱數(shù)值仿真條件子載波數(shù)（N）保護(hù)間隔長度（L）載波頻率偏差（g）信噪比（SNR）102412815信道條件為可加高斯白噪聲信道調(diào)制方式為QPSK調(diào)制方式。為了使接收數(shù)據(jù)中存在一個(gè)完整的包含循環(huán)前綴及其復(fù)制的原始數(shù)據(jù)符號部分，首先接收連續(xù)2N+L個(gè)符號數(shù)據(jù)，設(shè)OFDM符號的起始位置為d，定義兩個(gè)集合和一個(gè)2N+L長度的接收序列向量： （）可以看到，分別為循環(huán)前綴集合和OFDM符號中原始循環(huán)前綴的數(shù)據(jù)集，兩者數(shù)據(jù)是對應(yīng)相同的，而由于載波頻偏的存在，使得其對應(yīng)數(shù)據(jù)間有一個(gè)固定的相位偏差，兩者關(guān)系為：