📄 下一代移动无线通信系统的目标是实现无所不在的、高质量的、高速率的移动多媒体传输.htm
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<p class=MsoNormal><b><span style='font-size:14.0pt;mso-bidi-font-size:10.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman";color:fuchsia'>杨宝国</span></b><span lang=EN-US
style='font-size:15.0pt;mso-bidi-font-size:10.0pt;color:fuchsia'><o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:
10.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:
10.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:12.0pt;mso-bidi-font-size:10.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>论文题目：</span><span lang=EN-US style='font-size:12.0pt;
mso-bidi-font-size:10.0pt;font-family:宋体;color:blue'>OFDM无线通信系统中的定时恢复和信道估计算法</span><span
lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt;color:blue'><o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:
10.0pt;color:blue'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:12.0pt;mso-bidi-font-size:10.0pt;
font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>作者简介：</span><span style='font-size:12.0pt;mso-bidi-font-size:
10.0pt;font-family:宋体;color:#CC99FF'>杨宝国</span><span style='font-size:12.0pt;
mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";color:#CC99FF'>，男，</span><span
lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt;color:#CC99FF'>1973</span><span
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";color:#CC99FF'>年</span><span
lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt;color:#CC99FF'>01</span><span
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";color:#CC99FF'>月出生，</span><span
lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt;color:#CC99FF'>1996</span><span
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";color:#CC99FF'>年</span><span
lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt;color:#CC99FF'>07</span><span
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";color:#CC99FF'>月师从于</span><span
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;font-family:宋体;color:#CC99FF'>清华大学曹志刚</span><span
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";color:#CC99FF'>教授，于</span><span
lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt;color:#CC99FF'>2001</span><span
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";color:#CC99FF'>年</span><span
lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt;color:#CC99FF'>01</span><span
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";color:#CC99FF'>月获博士学位。</span><span
lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt;color:#CC99FF'><o:p></o:p></span></p>
<p class=MsoNormal align=center style='mso-margin-bottom-alt:auto;text-align:
center;text-indent:21.25pt;line-height:150%'><b><span lang=EN-US
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;letter-spacing:2.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></b></p>
<p class=MsoNormal align=center style='mso-margin-bottom-alt:auto;text-align:
center;text-indent:21.25pt;line-height:150%'><b><span lang=EN-US
style='font-size:12.0pt;mso-bidi-font-size:10.0pt;letter-spacing:2.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></b></p>
<p class=MsoNormal align=center style='mso-margin-bottom-alt:auto;text-align:
center;text-indent:21.25pt;line-height:150%'><b><span style='font-size:14.0pt;
mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";letter-spacing:2.0pt'>摘</span></b><b><span
style='font-size:14.0pt;mso-bidi-font-size:10.0pt;letter-spacing:2.0pt'> </span></b><b><span
style='font-size:14.0pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";letter-spacing:2.0pt'>要</span></b><span
lang=EN-US style='font-size:14.0pt;mso-bidi-font-size:10.0pt'><o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:1.0cm;line-height:150%'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman";letter-spacing:.5pt'>下一代移动无线通信系统的目标是实现无所不在的、高质量的、高速率的移动多媒体传输。但是为了实现这一目标，面临许多技术挑战。例如，移动无线通信系统面临的是十分恶劣的无线信道。稳健的移动无线通信系统不仅需要克服大的路径损耗，以及非常严重信号衰落，还要克服由于大的多径时延扩展而引起的符号间干扰。而正交频分复用</span><span
lang=EN-US style='letter-spacing:.5pt'>(Orthogonal Frequency Division
Multiplexing, OFDM)</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";letter-spacing:.5pt'>技术则是一种很有前途的、可克服信道时延扩展的传输手段。但是，</span><span
lang=EN-US style='letter-spacing:.5pt'>OFDM</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
letter-spacing:.5pt'>系统对于同步误差和信道估计误差都很敏感。针对上述问题，本文重点研究了</span><span lang=EN-US
style='letter-spacing:.5pt'>OFDM</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";letter-spacing:.5pt'>接收机中的定时恢复和信道估计算法。分别提出了一种包括码元同步和采样时钟同步在内的</span><span
lang=EN-US style='letter-spacing:.5pt'>OFDM</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
letter-spacing:.5pt'>系统定时恢复方案，一种适用于稀疏多径衰落信道、基于参数化信道模型的信道估计算法，以及一种低复杂度、基于加窗离散傅立叶变换的、针对非参数化信道模型的最小均方误差的信道估计算法。</span><span
lang=EN-US style='letter-spacing:.5pt'><o:p></o:p></span></p>
<p class=MsoPlainText style='text-indent:1.0cm;line-height:150%'><span
style='font-size:10.5pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-hansi-font-family:
"Courier New";letter-spacing:.5pt;mso-fareast-language:ZH-CN'>在第二章中，我们首先简要介绍有关无线通信信道的基本概念，并主要讨论多径信道的时延扩展对接收信号的影响。</span><span
lang=EN-US style='font-family:宋体;mso-hansi-font-family:"Courier New";
letter-spacing:.5pt;mso-fareast-language:ZH-CN'><o:p></o:p></span></p>
<p class=MsoPlainText style='text-indent:1.0cm;line-height:150%'><span
style='font-size:10.5pt;mso-bidi-font-size:10.0pt;font-family:宋体;mso-hansi-font-family:
"Courier New";letter-spacing:.5pt;mso-fareast-language:ZH-CN'>第三章主要讨论<span
lang=EN-US>OFDM系统接收机的设计问题。首先，我们介绍OFDM的基本原理，包括其理想的信号模型。特别是，我们引入了OFDM的块传输模型，从中我们可以看到循环前缀对于OFDM系统接收机的简化起着关键作用。然后，我们讨论当考虑了各种非同步因素后，OFDM系统的实际传输模型。其中，我们将OFDM接收机分成内接收机和外接收机来讨论。接着，我们分析了各种非理想传输条件对OFDM接收机性能的影响。最后，我们总结了实现OFDM内接收机中各部分功能的主要算法，并给出了一个OFDM内接收机的总体设计。<o:p></o:p></span></span></p>
<p class=MsoNormal style='text-indent:1.0cm;line-height:150%'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman";letter-spacing:.5pt'>论文第四章提出了一种包括实现</span><span lang=EN-US
style='letter-spacing:.5pt'>OFDM</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";letter-spacing:.5pt'>码元同步和采样时钟同步的定时恢复算法。在</span><span
lang=EN-US style='letter-spacing:.5pt'>OFDM</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
letter-spacing:.5pt'>传输系统中，同步的任务包括载波同步和定时恢复。而定时恢复又可进一步划分为</span><span
lang=EN-US style='letter-spacing:.5pt'>OFDM</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
letter-spacing:.5pt'>码元同步和采样时钟同步。码元同步的目的就是找到正确的</span><span lang=EN-US
style='letter-spacing:.5pt'>FFT</span><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";letter-spacing:.5pt'>窗位置。</span><span
lang=EN-US style='letter-spacing:.5pt'>OFDM</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
letter-spacing:.5pt'>码元的循环前缀可被用来做码元同步。但是在多径衰落信道中，由多径信道引起的</span><span
lang=EN-US style='letter-spacing:.5pt'>ISI</span><span style='font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
letter-spacing:.5pt'>已破坏了循环前缀的重复特性。在这种情况下，基于循环前缀的码元同步方法的性能将得不到保证。如果码元定时误差超出一定范围后，不准确的码元同步将引入</span><span
lang=EN-US style='letter-spacing:.5pt'>ISI</span><span style='font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
letter-spacing:.5pt'>，破坏各子载波之间的正交性，使</span><span lang=EN-US style='letter-spacing:
.5pt'>OFDM</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman";letter-spacing:.5pt'>系统性能下降。更严重的是，常用在相干</span><span
lang=EN-US style='letter-spacing:.5pt'>OFDM</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
letter-spacing:.5pt'>系统中，基于</span><span lang=EN-US style='letter-spacing:.5pt'>Wiener</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman";letter-spacing:.5pt'>滤波器的信道估计算法对码元同步误差非常敏感。所以，相干</span><span
lang=EN-US style='letter-spacing:.5pt'>OFDM</span><span style='font-family:
宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman";
letter-spacing:.5pt'>系统对码元同步准确性的要求更高。</span><span style='font-family:宋体;
mso-hansi-font-family:"Times New Roman";letter-spacing:.5pt'>另一方面，采样时钟同步的主要目的是使接收机和发射机的采样时钟频率保持一致。采样时钟频率偏差将导致<span
lang=EN-US>ICI。采样时钟频率偏差还将导致码元定时的漂移，进一步恶化码元同步的问题。而在已往算法中，采样时钟同步和码元同步没有有机地结合在一起。所以，我们提出一种基于导频的，包括码元和采时钟同步的OFDM传输系统定时恢复方法。在该方法中，我们用路径时延估计来提高基于相关算法的码元定时估计的准确性，并用一个反馈环路来跟踪采样时钟和锁定码元定时。我们提出了两种非相干反馈环路：DLL和MLL。该两种方法都可看成是在AWGN信道下，对码元定时和载波相位进行联合最大似然估计的递归解。我们分析了在AWGN信道下两种环路的跟踪误差均方值，并推导了对码元定时估计方差的CRB界。分析显示，MLL的跟踪误差的均方值渐近于该CRB界。而可以看成近似解的DLL，其性能相对于非近似解的MLL下降很小。另外，我们分别对以上算法在AWGN信道、非频率选择性衰落信道和多径衰落信道中进行了仿真，来验证其性能。结果表明，相对于传统的基于相关算法的码元同步方法而言，本章中提出的方法可将定时估计误差的均方值减小几个数量级。而且，这里提出的反馈环路方法可以跟踪由于采样时钟频差引起的码元定时漂移。<o:p></o:p></span></span></p>
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