OFDM论文：OFDM快变信道多普勒分集技术

1、OFDM论文：OFDM 快变信道 多普勒分集技术【中文摘要】由于具有信道频谱利用率高、实现容易（可采用快 速傅立叶变换）等优点，正交频分复用（OFDM 技术已成为高速数据传 输的关键技术，并被纳入第四代移动通信参考标准。然而，OFDM 系统 对频率偏差非常敏感，尤其在高速移动环境下，用户移动速度快，导致 信道的时变特性更加明显，多普勒频移和多普勒扩展更加显著，频率 偏差使 OFDM 系统子载波间的正交性遭到破坏，产生子载波间干扰 （ICI）,这将大大降低系统性能。本文从分集技术对抗多普勒效应和对 OFDM 系统性能的影响入手，研究高速移动环境下 OFDMS 带通信。本 文首先研究高速无线信道的

2、物理特性和数学模型，描述各种衰落信道 的特性,分析信道的时变特性对传输信号频谱的影响，给出了几个描 述衰落信道的常用函数，特别分析了高速移动环境下 OFDM 系统的关 键问题。随后介绍了OFDM 系统的基本原理及分集技术，分析了 OFDM 传输系统的基本原理，推出了 OFDh 时域和频域的模型，然后介绍了 OFDM 系统的优点和缺点，最后介绍了分集技术，着重讨论了比较常用 的几种分集方式。研究了它们各自的优缺点，最终得出分集技术的一 般实现规律和特点。本文主要研究内容是多普勒分集技术，把多普勒扩展作为频域分集资源，这样不但可以克服多普勒扩展对 OFDM 系统 的不利影响，还可以通过分集获得系统

3、性能的提高。在接收端,针对高 速移动环境下多普勒扩展明显的特性，研究了 OFDI 系统中的多普勒 分集技术,分析了一种适用于 OFDM 系统的简化多普勒分集技术，同时也研究了 MIMO-OFD 系统的多普勒分集技术。通过仿真，得出多普勒 分集技术和发射分集相结合可以更好的提高系统性能。在发射端，根 据高速列车通信的特点，提出了基于固定轨道的多普勒发射分集技术 同时提出了未来高速移动通信的宽带OFDM 军决方案,在现有的TD-SCDM 的高速铁路解决方案的基础上，解决应用多普勒分集技术的 难题,仿真结果表明，该技术有很大的优越性。【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