?? s02.htm
字號:
lang=EN-US style="FONT-SIZE: 12pt">? </SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">簡單的回答就是主要為了通信的安全可靠。</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; LINE-HEIGHT: 150%"><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><SPAN
style="mso-spacerun: yes"> </SPAN><SPAN
style="mso-spacerun: yes"> </SPAN></SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">擴頻通信的基本特點，是傳輸信號所占用的頻帶寬度</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(W)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">遠大于原始信息本身實際所需的最小</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; 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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">帶寬</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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，其比值稱為處理增益</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Gp:<O:P> </O:P></SPAN></P>
<P class=MsoNormal
style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%"
align=center><SPAN lang=EN-US style="FONT-SIZE: 12pt"><SPAN
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>
<P class=MsoNormal
style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%"
align=center> </P>
<P class=MsoNormal
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lang=EN-US
style="FONT-SIZE: 12pt; mso-spacerun: yes">
</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">眾所周知，任何信息的有效傳輸都需要一定的頻率寬度，如話音為</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">1.7 --- 3.1kHz</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，電視圖像則寬到數兆赫。為了充分利用有限的頻率資源，增加通路數目，人們廣泛選擇不同調制方式，采用寬頻信道</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">同軸電纜、微波和光纖等</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，和壓縮頻帶等措施，同時力求使傳輸的媒介中傳輸的信號占用盡量窄的帶寬。因現今使用的電話、廣播系統中，無論是采用調幅、調頻或脈沖編碼調制制式，</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Gp</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">值一般都在十多倍范圍內，統稱為“窄帶通信”。而擴頻通信的</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Gp</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">值，高達數百、上千，稱為</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt; mso-spacerun: yes">
</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">“寬帶通信”。</SPAN></P>
<P class=MsoNormal
style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21.75pt; LINE-HEIGHT: 150%"> </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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">擴頻通信的可行性，</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt; mso-spacerun: yes">
</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是從信息論和抗干擾理論的基本公式中引伸而來的。</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%"><FONT
color=#0000ff><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">信息論中關于信息容量的仙農</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(Shannon)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">公式為：</SPAN></FONT><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%"
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: 宋體; 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: 宋體; 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>
<P class=MsoNormal
style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21.75pt; LINE-HEIGHT: 150%"
align=center><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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">式中：</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">C --- </SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; 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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">用傳輸速率度量</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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">信號頻帶寬度</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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">信號功率</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
lang=EN-US style="FONT-SIZE: 12pt">N --- </SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">白噪聲功率</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: 宋體; 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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">說明，在給定的傳輸速率</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">C</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">不變的條件下，頻帶寬度</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">W</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; 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: 宋體; 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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是可以互換的。即可通過增加頻帶寬度的方法，在較低的信噪比</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">P</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; 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: 宋體; 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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">情況下，傳輸信息。</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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">擴展頻譜換取信噪比要求的降低，正是擴頻通信的重要特點，并由此為擴頻通信的應用奠定了基礎。</SPAN></P>
<P class=MsoNormal
style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21.75pt; LINE-HEIGHT: 150%"> </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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
color=#0000ff>擴頻通信可行性的另一理論基礎，為柯捷爾尼可夫關于信息傳輸差錯概率的公式：</FONT></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%"
align=center><SPAN lang=EN-US style="FONT-SIZE: 12pt"><SPAN
style="mso-spacerun: yes">
</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: 宋體; 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>
<P class=MsoNormal
style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21.75pt; LINE-HEIGHT: 150%"
align=center><SPAN lang=EN-US
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