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<TD borderColor=#6699ff><FONT size=2>您的位置：技術園地>技術講座-擴頻通信</FONT></TD></TR>
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<DIV align=center><FONT color=#000080 size=5><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><B>第三講 擴展頻譜通信的主要特點</B></SPAN></FONT><FONT
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style="mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><FONT
face=楷體_GB2312 color=#ff9900 size=5>由</FONT></SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">于擴頻通信能大大擴展信號的頻譜，發端用擴頻碼序列進行擴頻調制，<BR>以及在收端用相關解調技術，使其具有許多窄帶通信難于替代的優良性能，<BR>能在“軍轉民”后，迅速推廣到各種公用和專用通信網絡之中，主要有以下幾<BR>項特點：</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><SPAN
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<P class=MsoNormal
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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%"><B><SPAN
lang=EN-US><FONT color=#800080 size=4><A
name="3.1 易于重復使用頻率，提高了無線頻譜利用率">3.1<SPAN
style="mso-spacerun: yes"> </SPAN></A></FONT></SPAN><FONT
color=#800080 size=4><A name="3.1 易于重復使用頻率，提高了無線頻譜利用率"><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">易于重復使用頻率，提高了無線頻譜利用率</SPAN></A></FONT></B><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
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<SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">無線頻譜十分寶貴，雖然從長波到微波都得到了開發利用，仍然滿足不了社會的需求。在窄帶通信中，主要依靠波道劃分來防止信道之間發生干擾。</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
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<SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">為此，世界各國都設立了頻率管理機構，用戶只能使用申請獲準的頻率。</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
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<SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">擴頻通信發送功率極低</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(1 --- 650mW)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，采用了相關接收這一高技術，且可工作在信道噪聲和熱噪聲背景中，易于在同一地區重復使用同一頻率</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'">也可與現今各種窄道通信共享同一頻率資源。所以，在美國及世界絕大多數國家，擴頻通信不需申請頻率，任何個人與單位可以無執照使用。</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"> </SPAN></P>
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<P class=MsoNormal
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lang=EN-US><FONT color=#800080 size=4><A
name="3.2 抗干擾性強，誤碼率低">3.2<SPAN style="mso-spacerun: yes">
</SPAN></A></FONT></SPAN><FONT color=#800080 size=4><A
name="3.2 抗干擾性強，誤碼率低"><SPAN
style="FONT-FAMILY: 宋體; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">抗干擾性強，誤碼率低</SPAN></A></FONT></B><SPAN
lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
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<SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">擴頻通信在空間傳輸時所占有的帶寬相對較寬，而收端又采用相關檢測的辦法來解擴，使有用寬帶信息信號恢復成窄帶信號，而把非所需信號擴展成寬帶</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，然后通過窄帶濾波技術提取有用的信號。這祥，對于各種干擾信號，因其在收端的非相關性，解擴后窄帶信號中只有很微弱的成份，信噪比很高，因此抗干擾性強。</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'">如上述例子（第二講），</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'">當</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Gp = 35dB</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">時，抗干擾容限</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Mj = 22dB</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，即在負信噪聲比</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'">－</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">22dB)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">條件下，可以將信號從噪聲的湮滅中提取出來。</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'">在目前商用的通信系統中，</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt; mso-spacerun: yes">
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