1、OFDM論文：OFDM 快變信道 多普勒分集技術【中文摘要】由于具有信道頻譜利用率高、實現容易（可采用快 速傅立葉變換）等優點，正交頻分復用（OFDM 技術已成為高速數據傳 輸的關鍵技術，并被納入第四代移動通信參考標準。然而，OFDM 系統 對頻率偏差非常敏感，尤其在高速移動環境下，用戶移動速度快，導致 信道的時變特性更加明顯，多普勒頻移和多普勒擴展更加顯著，頻率 偏差使 OFDM 系統子載波間的正交性遭到破壞，產生子載波間干擾 （ICI）,這將大大降低系統性能。本文從分集技術對抗多普勒效應和對 OFDM 系統性能的影響入手，研究高速移動環境下 OFDMS 帶通信。本 文首先研究高速無線信道的

2、物理特性和數學模型，描述各種衰落信道 的特性,分析信道的時變特性對傳輸信號頻譜的影響，給出了幾個描 述衰落信道的常用函數，特別分析了高速移動環境下 OFDM 系統的關 鍵問題。隨后介紹了OFDM 系統的基本原理及分集技術，分析了 OFDM 傳輸系統的基本原理，推出了 OFDh 時域和頻域的模型，然后介紹了 OFDM 系統的優點和缺點，最后介紹了分集技術，著重討論了比較常用 的幾種分集方式。研究了它們各自的優缺點，最終得出分集技術的一 般實現規律和特點。本文主要研究內容是多普勒分集技術，把多普勒擴展作為頻域分集資源，這樣不但可以克服多普勒擴展對 OFDM 系統 的不利影響，還可以通過分集獲得系統

3、性能的提高。在接收端,針對高 速移動環境下多普勒擴展明顯的特性，研究了 OFDI 系統中的多普勒 分集技術,分析了一種適用于 OFDM 系統的簡化多普勒分集技術，同時也研究了 MIMO-OFD 系統的多普勒分集技術。通過仿真，得出多普勒 分集技術和發射分集相結合可以更好的提高系統性能。在發射端，根 據高速列車通信的特點，提出了基于固定軌道的多普勒發射分集技術 同時提出了未來高速移動通信的寬帶OFDM 軍決方案,在現有的TD-SCDM 的高速鐵路解決方案的基礎上，解決應用多普勒分集技術的 難題,仿真結果表明，該技術有很大的優越性。【英文摘要】 Because of the high spectr

4、um efficiency,easeof implementation (via Fast Fourier Transform) and so on, orthog onalfreque ncy divisio n multiplex ing (OFDM) tech no logy has becomethekey tech no logy of high-speed data tran smissi on, and has bee nadopted by the fourth gen erati on mobile com muni cati on. ButOFDMystems are ve

5、ry sen sitive to freque ncy deviati on, particularly inhigh-speed mobile en vir onment.Because the user moves fast, the channel s time-varying characteristicsis obvious, the Doppler shift and Doppler spread are significant.Thesecause the frequency offset, thusthe orthog on ality betwee n OFDM sub-ca

6、rriers is destroyed, whichresults in inter-carrier interferenee(ICI) and greatlyreduces the system performanee. In this thesis we focus on the Dopplereffects which affect OFDkftignificantly,and study keytech no logies of OFDM in high-speed mobile com muni cati ons.ln thisthesis we study the physical

7、 properties and mathematicalmodel of high-speed wireless cha nn els, describe the characteristics ofseveral fadi ng cha nn els, and an alyze the impact of time-vary ing channel on sig nal spectrum. We an alyze several com mon fadi ng cha nn els fun cti on, and mainly focus on the key tech niq ues of

8、 OFDM systemsun der high-speed mobile en vir onment. The n we in troduce the OFDMsystems basic principle and diversity techniques, give OFDM timedomain and freque ncy domai n model, and discuss the OFDM systems adva ntages and disadva ntages. Fin ally we in troduce diversity tech niques and several

9、com monly used methods. The adva ntages and disadvantages of diversity are an alyzed, and the gen eral rules andcharacteristics of diversity tech niq ues are give n. The mai n word of thisthesis is Doppler diversity tech no logy. Wetake the Doppler spread as afreque ncy diversity resource, which not

10、 only overcomes the impact ofDoppler spread on OFDM systems, but also improves the performa nee ofsystem through diversity. At the receiver, we study Doppler diversity forOFDM systems under high-speed mobile environment, analyze asimplified Doppler diversitytech no logy for OFDMystems, anddiscuss the Doppler div