s04.htm

扩频通信讲座

            color=#0080c0><B><A 
            name="4.2.1  直接序列扩频(Direct Sequence Spread Spectrum)工作方式，简称直扩(DS)方式"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">直接序列扩频</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(Direct Sequence Spread 
            Spectrum)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">工作方式，简称直扩</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'">方式</SPAN></A></B></FONT></P>
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            <SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">所谓直接序列</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(DS-Direct Scquency)</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，就是直接用具有高码率的扩频码序列在发端去扩展信号的频谱。而在收端，用相同的扩频码序列去进行解扩，把展宽的扩频信号还原成原始的信息。直接序列扩频的原理如图</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">1</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=389 src="s04.files/b2.gif" width=450 border=0><O:P> 
            </O:P></SPAN></P>
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            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">1<SPAN 
            style="mso-spacerun: yes">&nbsp;</SPAN></SPAN></P>
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            align=center><SPAN lang=EN-US style="FONT-SIZE: 12pt"><SPAN 
            style="mso-spacerun: yes">&nbsp; </SPAN><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'">例如我们用窄脉冲序列对某一载波进行二相相移键控调制。如果采用平衡调制器，则调制后的输出为二相相移键控信号，它相当于载波抑制的调幅双边带信号。图中输入载波信号的频率为</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">fc</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，窄脉冲序列的频谱函数为</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">G(C)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，它具有很宽的频带。平衡调制器的输出则为两倍脉冲频谱宽度，而</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">fc</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">被抑制的双边带的展宽了的扩频信号，其频谱函数为</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">fc </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"> G(C)</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></P>
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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'">在接收端应用相同的平衡调制器作为解扩器。可将频谱为</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">fc</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">G(C) </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的扩频信号，用相同的码序列进行再调制，将其恢复成原始的载波信号</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">fc</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></P>
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            lang=EN-US style="FONT-SIZE: 12pt"><B><FONT color=#0080c0><A 
            name="4.2.2  跳变频率(Frequency Hopping)工作方式，简称跳频(FH)方式">4.2.2<SPAN 
            style="mso-spacerun: yes">&nbsp; 
            </SPAN></A></FONT></B></SPAN><B><FONT color=#0080c0><A 
            name="4.2.2  跳变频率(Frequency Hopping)工作方式，简称跳频(FH)方式"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">跳变频率</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(Frequency Hopping)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">工作方式，简称跳频</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'">方式</SPAN></A></FONT></B></P>
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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'">另外一种扩展信号频谱的方式称为跳频</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">Frequency Hopping)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。所谓跳频，比较确切的意思是：用一定码序列进行选择的多频率频移键控。也就是说，用扩频码序列去进行频移键控调制，使载波频率不断地跳变，所以称为跳频。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
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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'">简单的频移键控如</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">2FSK</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，只有两个频率，分别代表传号和空号。而跳频系统则有几个、几十个、甚至上干个频率、由所传信息与扩频码的组合去进行选择控制，不断跳变。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
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            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%"><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">2(a)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">为跳频的原理示意图。发端信息码序列与扩频码序列组合以后按照不同的码字去控制频率合成器。</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'">从图</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">2(b)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中可以看出在频域上输出频谱在一宽频带内所选择的某些频率随机地跳变。在收端，为了解跳跳频信号，需要有与发端完全相同的本地扩频码发生去控制本地频率合成器，使其输出的跳频信号能在混频器中与接收信号差频出固定的中频信号，然后经中频带通滤波器及信息解调器输出恢复的信息。</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=376 src="s04.files/b3.gif" width=450 border=0><O:P> 
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            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">2 (a) ,<SPAN 
            style="mso-spacerun: yes">&nbsp; </SPAN>(b)<O:P> </O:P></SPAN></P>
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