【正文】 題，因此應(yīng)該對該算法進行了改進，理論分析表明改進后的算法，提高了時頻估計性能。 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，得到無線通信專家的廣泛關(guān)注， 并成為下一代移動通信最具競爭力的關(guān)鍵傳輸技術(shù)之一。另一方面，與單載波傳輸系統(tǒng)相比，OFDM 系統(tǒng)對同步誤差十分敏感，因此系統(tǒng)同步是 OFDM 傳輸中的關(guān)鍵問題。本文主要研究OFDM 系統(tǒng)中的同步問題。本文主要做了以下幾方面的工作：綜述當前通信領(lǐng)域的發(fā)展狀況，引出 OFDM 技術(shù)研究的重要性,介紹了OFDM 技術(shù)的發(fā)展歷程。研究了 OFDM 系統(tǒng)的原理,并對系統(tǒng)性能的優(yōu)缺點和關(guān)鍵技術(shù)進行了歸納。研究了 OFDM 系統(tǒng)的同步原理，分析了定時偏移和載波頻率偏移對OFDM 系統(tǒng)接收機性能的影響，分析的結(jié)果表明頻率偏移對系統(tǒng)的性能影響最大，必須使頻率偏差控制在很小的范圍內(nèi)。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。使用最大似然理論推導出了估計算法，在基于循環(huán)前綴的同步算法中，針對原有的算法進行了仿真，仿真試驗結(jié)果與預(yù)期相同。 本文的研究還有許多需要完善改進的地方，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間和復(fù)雜度等問題。下一步可以針對這兩方面進一步研究。 本文只是對算法進行了研究，仿真的信道環(huán)境比較簡單，與實際應(yīng)用系統(tǒng)還有一定的距離。如何在瑞利衰落信道下或與實際相接近的系統(tǒng)來考慮同步問題，有待進一步研究。 由于受到時間和本人學習水平的限制，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。致謝在四年的學習生活當中，我首先要感謝我的導師王桂寶教授，從他身上我不僅學到了科學的研究方法和技能，而且還認識到嚴謹求實的學術(shù)作風。他平易近人，從治學到為人，都讓我受益匪淺，無不潛移默化地影響我的人生。王老師除了在工作和學習上給我很多的指導和有益的建議，在生活上也給我極大的幫助。在此表示由衷的感謝。感謝我們這一組的朱貝貝同學，黨蕊萍同學，郝曉燕同學，劉博濤同學及實驗室所有同學，在共同工作和學習中，大家互相幫助和鼓勵。 在實驗室工作及撰寫論文期間，賈雄雄、張前鋒等同學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。在此向他們表達我的感激之情。 參考文獻[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],. 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