g3-10.htm

介绍移动通信gsm原理的书籍

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            style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'"><FONT 
            size=3>&nbsp;<O:P> </O:P></FONT></SPAN></P>
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            size=3>射频跳频是将话音信号用固定的发射机，由跳频序列控制，采用不同频率发射，原理图如图<SPAN 
            lang=EN-US>3-37所示，实施框图如图3-38所示。需要说明的是，射<SPAN 
            style="mso-hansi-font-family: Times New Roman; mso-spacerun: yes">&nbsp; 
            </SPAN>频跳频必须有两个发射机，一个固定发射载频Fo，因它带有控制信道BCCH；另一发射机载波频率可随着跳频序列的序列值的改变而改变。<O:P> 
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            style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'"><FONT 
            size=3>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
            <IMG height=83 src="g3-10.files/g3-10.3.gif" width=293 
            v:shapes="_x0000_i1027"><O:P> </O:P></FONT></SPAN></P>
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            style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'"><FONT 
            face=楷体_GB2312 color=#000066 size=3>图<SPAN lang=EN-US>3-37 射频跳频<O:P> 
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            v:shapes="_x0000_i1028"><O:P> </O:P></FONT></SPAN></P>
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            align=center><SPAN 
            style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'"><FONT 
            face=楷体_GB2312 color=#000066 size=3>图<SPAN lang=EN-US>3-38 
            射频跳频实施框图<O:P> </O:P></SPAN></FONT><FONT face=楷体_GB2312 size=3><SPAN 
            lang=EN-US><O:P></O:P></SPAN></FONT><FONT face=楷体_GB2312 
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            style="mso-hansi-font-family: Times New Roman; mso-spacerun: yes">&nbsp;&nbsp;&nbsp; 
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            size=3>射频跳频比基带跳频具有更高的性能改善和抗同频干扰能力，但其缺点是：</FONT><FONT size=3><SPAN 
            lang=EN-US><O:P> </O:P></SPAN></FONT></SPAN></P>
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            style="FONT-FAMILY: 宋体; mso-hansi-font-family: Times New Roman; mso-spacerun: yes">&nbsp;&nbsp;&nbsp; 
            </SPAN><FONT face=楷体_GB2312 color=#000066>(1) <SPAN lang=EN-US 
            style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'">射频跳频目前还不成熟。<O:P> 
            </O:P></SPAN></FONT></SPAN></FONT></P>
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            style="FONT-FAMILY: 宋体; mso-hansi-font-family: Times New Roman; mso-spacerun: yes">&nbsp;&nbsp;&nbsp; 
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            射频跳频只有当每小区拥有4个频率以上时效果比较明显。<O:P> </O:P></SPAN></FONT><SPAN lang=EN-US 
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            <O:P></O:P></SPAN></SPAN></FONT></P>
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            </SPAN>(3)<SPAN lang=EN-US 
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            射频跳频必须使用HIBRID合成器，每小区如使用4个载频就需要配置3个HIBRID，损耗约6dB，比空腔合成器的损耗大3dB 
            左右。对基站覆盖范围有一定影响。<O:P> </O:P></SPAN></SPAN></FONT></P>
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            style="mso-hansi-font-family: Times New Roman">(4)<SPAN lang=EN-US 
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            合成器要求网路中各基站必须同步，而目前很多供货商难满足。<O:P> </O:P></SPAN></SPAN></FONT></P>
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            <O:P></O:P></SPAN></SPAN></FONT><FONT 
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            <O:P></O:P></SPAN></SPAN></FONT></P>
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            style="mso-hansi-font-family: Times New Roman; mso-spacerun: yes">&nbsp;&nbsp;&nbsp; 
            </SPAN><FONT face=楷体_GB2312 
            color=#000066>综上原因，大多数厂家的BTS是采用基带跳频技术，而不采射频跳频技术。<O:P> 
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      size=2>版权所有：移动通信国家工程研究中心 
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