📄 s02.htm
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lang=EN-US 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'">简单的回答就是主要为了通信的安全可靠。</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'">扩频通信的基本特点，是传输信号所占用的频带宽度</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(W)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">远大于原始信息本身实际所需的最小</SPAN><SPAN
lang=EN-US 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'">有效</SPAN><SPAN
lang=EN-US 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'">带宽</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(</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">D</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">F)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，其比值称为处理增益</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Gp:<O:P> </O:P></SPAN></P>
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style="mso-spacerun: yes"> <B> </B></SPAN><B>Gp =
W/</B></SPAN><B><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">D</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">F<SPAN
style="mso-spacerun: yes"> ......
</SPAN>(1)</SPAN></B></P>
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align=center> </P>
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</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">众所周知，任何信息的有效传输都需要一定的频率宽度，如话音为</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">1.7 --- 3.1kHz</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，电视图像则宽到数兆赫。为了充分利用有限的频率资源，增加通路数目，人们广泛选择不同调制方式，采用宽频信道</SPAN><SPAN
lang=EN-US 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'">同轴电缆、微波和光纤等</SPAN><SPAN
lang=EN-US 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'">，和压缩频带等措施，同时力求使传输的媒介中传输的信号占用尽量窄的带宽。因现今使用的电话、广播系统中，无论是采用调幅、调频或脉冲编码调制制式，</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Gp</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">值一般都在十多倍范围内，统称为“窄带通信”。而扩频通信的</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Gp</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">值，高达数百、上千，称为</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'">“宽带通信”。</SPAN></P>
<P class=MsoNormal
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<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'">扩频通信的可行性，</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'">是从信息论和抗干扰理论的基本公式中引伸而来的。</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
<P class=MsoNormal
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color=#0000ff><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">信息论中关于信息容量的仙农</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(Shannon)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">公式为：</SPAN></FONT><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"><SPAN
style="mso-spacerun: yes"> <B> </B></SPAN><B>C
</B></SPAN><B><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"> WLog<SUB>2</SUB>(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'">十</SPAN></B><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><B>P/N)<SPAN
style="mso-spacerun: yes"> ......
</SPAN>(2)</B></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; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">式中：</SPAN></P>
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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'">信道容量</SPAN><SPAN
lang=EN-US 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'">用传输速率度量</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">)<O:P> </O:P></SPAN></P>
<P class=MsoNormal
style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21.75pt; LINE-HEIGHT: 150%"><SPAN
lang=EN-US style="FONT-SIZE: 12pt">W --- </SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">信号频带宽度</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
<P class=MsoNormal
style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21.75pt; LINE-HEIGHT: 150%"><SPAN
lang=EN-US style="FONT-SIZE: 12pt">P --- </SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">信号功率</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
<P class=MsoNormal
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lang=EN-US style="FONT-SIZE: 12pt">N --- </SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">白噪声功率</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
<P class=MsoNormal
style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21.75pt; 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'">式</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'">说明，在给定的传输速率</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'">不变的条件下，频带宽度</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">W</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">和信噪比</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">P</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">N</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是可以互换的。即可通过增加频带宽度的方法，在较低的信噪比</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">P</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">N(S</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">N)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">情况下，传输信息。</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'">扩展频谱换取信噪比要求的降低，正是扩频通信的重要特点，并由此为扩频通信的应用奠定了基础。</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'"><FONT
color=#0000ff>扩频通信可行性的另一理论基础，为柯捷尔尼可夫关于信息传输差错概率的公式：</FONT></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"><SPAN
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</SPAN><B>Pow<SUB>j<SPAN style="mso-spacerun: yes">
</SPAN></SUB></B></SPAN><B><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
lang=EN-US style="FONT-SIZE: 12pt"><SPAN
style="mso-spacerun: yes"> </SPAN>f(E/N</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></B><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><B>)<SPAN
style="mso-spacerun: yes"> ......
</SPAN>(3)</B></SPAN></P>
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