s04.htm

扩频通信讲座

            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在上述几种基本的扩频方式的基础上，可以组合起来，构成各种混合方式。例如</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">／</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">／</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">TH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">／</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">／</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">TH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">等等。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">一般说来，采用混合方式看起来在技术上要复杂一些，实现起来也要困难一些。但是，不同方式结合起来的优点是有时能得到只用其中一种方式得不到的特性。例如</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">／</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">系统，就是一种中心频率在某一领带内跳变的直接序列扩频系统。其信号的频谱如图</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">4</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">5</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">所示。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
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            align=center><SPAN lang=EN-US style="FONT-SIZE: 12pt">&nbsp;<IMG 
            height=142 src="s04.files/b6.gif" width=450 border=0><O:P> 
            </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; TEXT-ALIGN: center; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt" 
            align=center><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">图</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">4</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">5<O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">由图可见，一个</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">扩频信号在一个更宽的频带范围内进行跳变。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS/FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">系统的处理增益为</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">和</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">处理增益之和。因此，有时采用</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS/FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">反而比单独采用</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">或</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">获得更宽的频谱扩展和更大的处理增益。甚至有时相对来说，其技术复杂性比单独用</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">来展宽频谱或用</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在更宽的范围内实现频率的跳变还要容易些。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">对于</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">／</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">TH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">方式，它相当于在扩频方式中加上时间复用。采用这种方式可以容纳更多的用户。在实现上，</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">本身已有严格的收发两端扩频码的同步。加上跳时，只不过增加了一个通－断开关，并不增加太多技术上的复杂性。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">对于</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">／</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">／</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">TH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，它把三种扩频方式组合在一起，在技术实现上肯定是很复杂的。但是对于一个有多种功能要求的系统，</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">DS</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">FH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">TH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">可分别实现各自独特的功能。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">因此，对于需要同时解决诸如抗干扰、多址组网、定时定位、抗多径和远－近问题时，就不得不同时采用多种扩频方式。</SPAN></P></TD>
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