s05-03.htm

关于扩频的一些好资料

            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">7(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'">中所示。</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'">平衡调制器的一个重要特性是输出的调制信号是载波抑制的。这对于扩频通信是很重要的。无载波发射，既可节省功率，又可使扩频信号更加隐蔽，不易被</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt; mso-spacerun: yes">&nbsp; 
            </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">发觉。平衡调制器对两个输入信号来说相当于乘法器。</SPAN><SPAN 
            style="FONT-SIZE: 12pt"> </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">如果载波信号用</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">Acos</SPAN><SPAN lang=EN-US 
            style="FONT-SIZE: 12pt; FONT-FAMILY: Symbol; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman; mso-char-type: symbol; mso-symbol-font-family: Symbol">v</SPAN><SUB><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">c</SPAN></SUB><SPAN lang=EN-US 
            style="FONT-SIZE: 12pt">t</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">表示，脉冲信号用</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">m(t)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">表示，则输出信号为二者乘积：</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">A[m(t)]cos</SPAN><SPAN lang=EN-US 
            style="FONT-SIZE: 12pt; FONT-FAMILY: Symbol; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman; mso-char-type: symbol; mso-symbol-font-family: Symbol">v</SPAN><SUB><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">c</SPAN></SUB><SPAN lang=EN-US 
            style="FONT-SIZE: 12pt">t<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'">如果</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">m(t)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">取值为土</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">l</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，则输出信号根据三角公式可分解为相位相差</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">180</SPAN><SPAN lang=EN-US 
            style="FONT-SIZE: 12pt; FONT-FAMILY: Symbol; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman; mso-char-type: symbol; mso-symbol-font-family: Symbol">°</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的两个分量之和如图</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'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">7(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'">所示，它相当于只有两个边频而无载波。但在直扩系统</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt; mso-spacerun: yes"> </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，调制脉冲不是周期性的规则脉冲，而是</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">PN</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">码脉冲序列。</SPAN></P>
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            align=center><IMG height=444 src="s05-03.files/s5-5.gif" width=450 
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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">图5-7 
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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"></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"></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'">在图</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'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">2</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中已示出周期性的脉冲序列的频谱，而是呈</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">[(sinx/x)<SUP>2</SUP></SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">型的分布。因此，实际</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">PN</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">码调制载波获得的功率谱边呈</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">[(sinx/x)<SUP>2</SUP></SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">型分布，如图</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'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">8(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'">所示，它好像是分布为</SPAN><SPAN 
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            [(sinx)/x]<SUP>2</SUP></SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的噪声一样。图中这一波型是比较理想的平衡调制器的波型。实际的平衡调制器，有时不能做到真正平衡。因此，可能出现载波不能完全抑制，或调制的</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">PN</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">脉冲信号有泄漏，以及钟脉冲信号泄漏到输出端的情况。图</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'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">8(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'">，</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(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><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(d)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">分别示出这三种情况的输出波形。当然，它们都是我们所不希望的和应尽量想法避免的。</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=321 src="s05-03.files/s5-6.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">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'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">8<O:P> </O:P></SPAN></P>
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            align=center><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; mso-spacerun: yes">&nbsp;&nbsp;&nbsp;&nbsp;</SPAN></P>
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            style="FONT-SIZE: 12pt; mso-spacerun: yes">&nbsp;&nbsp;&nbsp; 
            </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">除了</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">BPSK</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">调制获得扩频信号外，还可以采用</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">QPSK</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">及</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">MSK</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">调制来进行扩频调制。</SPAN><SPAN