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<TD borderColor=#6699ff><FONT size=2>您的位置：技术园地>技术讲座-扩频通信</FONT></TD></TR>
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<DIV align=center><FONT color=#000080 size=5><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><B>第三讲 扩展频谱通信的主要特点</B></SPAN></FONT><FONT
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face=楷体_GB2312 color=#ff9900 size=5>由</FONT></SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">于扩频通信能大大扩展信号的频谱，发端用扩频码序列进行扩频调制，<BR>以及在收端用相关解调技术，使其具有许多窄带通信难于替代的优良性能，<BR>能在“军转民”后，迅速推广到各种公用和专用通信网络之中，主要有以下几<BR>项特点：</SPAN><SPAN
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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 易于重复使用频率，提高了无线频谱利用率">3.1<SPAN
style="mso-spacerun: yes"> </SPAN></A></FONT></SPAN><FONT
color=#800080 size=4><A name="3.1 易于重复使用频率，提高了无线频谱利用率"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">易于重复使用频率，提高了无线频谱利用率</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: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">无线频谱十分宝贵，虽然从长波到微波都得到了开发利用，仍然满足不了社会的需求。在窄带通信中，主要依靠波道划分来防止信道之间发生干扰。</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: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">为此，世界各国都设立了频率管理机构，用户只能使用申请获准的频率。</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: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">扩频通信发送功率极低</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(1 --- 650mW)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，采用了相关接收这一高技术，且可工作在信道噪声和热噪声背景中，易于在同一地区重复使用同一频率</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'">也可与现今各种窄道通信共享同一频率资源。所以，在美国及世界绝大多数国家，扩频通信不需申请频率，任何个人与单位可以无执照使用。</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt"> </SPAN></P>
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lang=EN-US><FONT color=#800080 size=4><A
name="3.2 抗干扰性强，误码率低">3.2<SPAN style="mso-spacerun: yes">
</SPAN></A></FONT></SPAN><FONT color=#800080 size=4><A
name="3.2 抗干扰性强，误码率低"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">抗干扰性强，误码率低</SPAN></A></FONT></B><SPAN
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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'">扩频通信在空间传输时所占有的带宽相对较宽，而收端又采用相关检测的办法来解扩，使有用宽带信息信号恢复成窄带信号，而把非所需信号扩展成宽带</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，然后通过窄带滤波技术提取有用的信号。这祥，对于各种干扰信号，因其在收端的非相关性，解扩后窄带信号中只有很微弱的成份，信噪比很高，因此抗干扰性强。</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'">如上述例子（第二讲），</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'">当</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Gp = 35dB</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">时，抗干扰容限</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">Mj = 22dB</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，即在负信噪声比</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'">－</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">22dB)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">条件下，可以将信号从噪声的湮灭中提取出来。</SPAN></P>
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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'">在目前商用的通信系统中，</SPAN><SPAN
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