📄 g3-1.htm
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face=楷体_GB2312 color=#000066>图<SPAN lang=EN-US>3-3 900MHz
3／9方式频道分配图<O:P> </O:P></SPAN></FONT></SPAN></P>
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style="mso-hansi-font-family: Times New Roman"> </SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">因总的频道数<SPAN
lang=EN-US>N是固定的，所以分组数F越少则每组的频道数就越多。但是，频率分组数的减少也使同频道复用距离减小，导致系统中平均C／I值降低。因此，在工程实际使用中是把同频干扰保护</SPAN><FONT
size=3>比<SPAN
lang=EN-US>C／I值加3dB的冗余来保护，采用12分组方式，即4个基站，12组频率(见图3-2和图3-4所示)。</SPAN></FONT></SPAN><SPAN
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color=#000066>图<SPAN lang=EN-US>3-4 频率复用方式<O:P>
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style="mso-hansi-font-family: Times New Roman"> </SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">对于有向天线而言，天线可采用<SPAN
lang=EN-US>120</SPAN></SPAN><SPAN lang=EN-US
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style="mso-hansi-font-family: Times New Roman">或<SPAN
lang=EN-US>60</SPAN></SPAN><SPAN lang=EN-US
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style="mso-hansi-font-family: Times New Roman">的定向天线，形成三叶草小区，即把基站分成<SPAN
lang=EN-US>3个扇形小区。如采用4／12复用方式，每个小区最大可用到5个频道，一般的也可用到4个频道。如采用3／9复用方式，则每个小区可用到6个或5个频道。</SPAN></SPAN><SPAN
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size=3>对于无方向性天线，即全向天线建议采用<SPAN
lang=EN-US>7组频率复用方式，其7组频率可从12组中任选，但相邻频率组尽量不在相邻小区使用(见图3-5)。业务量较大的小区可借用剩余的频率组，如使用第9组的小区可借用第2组频率等。<O:P>
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color=#000066 size=3>图<SPAN lang=EN-US>3-5<SPAN
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</SPAN>7小区分组</SPAN></FONT></SPAN><FONT face=楷体_GB2312
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style="mso-hansi-font-family: Times New Roman"> 以上所谈每小区可用频道数都是在可用频段为<SPAN
lang=EN-US>10MHz情况下，目前10MHz中4MHz为邮电部使用，另6MHz为</SPAN></SPAN><SPAN
lang=EN-US style="mso-ascii-font-family: 宋体">“</SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">中国联通公司</SPAN><SPAN
lang=EN-US style="mso-ascii-font-family: 宋体">”</SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">使用。从频道序号来看，<SPAN
lang=EN-US>76～95为邮电部使用，95～124为</SPAN></SPAN><SPAN lang=EN-US
style="mso-ascii-font-family: 宋体">“</SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">中国联通公司</SPAN><SPAN
lang=EN-US style="mso-ascii-font-family: 宋体">”</SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">使用。这样，邮电部建的<SPAN
lang=EN-US>GSM数字移动通信网如采用4／12频率复用方式时，每小区可用频道数最大仅有2个(16个信道)，有些只能用到1个(8个信道)。为此，邮电部下属大部分邮电管理局将4MHz带宽向下端扩展2MHz，即占用模拟B网2MHz，使GSM数字移动通信网从可用频道76～95(20个)扩展到66～95(30个)，4／12方式每个小区一般可用3个频道(24信道)，最小也能用到2个频道(16个信道)。</SPAN></SPAN></FONT><FONT
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<P class=MsoNormal><SPAN lang=EN-US
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style="mso-spacerun: yes"> </SPAN></FONT><B><FONT
size=3><SPAN style="mso-spacerun: yes"> </SPAN>(7)
保护带宽：400kHz<O:P> </O:P></FONT></B></SPAN></P>
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color=#000066>当一个地区数字移动通信系统与模拟移动通信系统共存时，两系统之间<SPAN
lang=EN-US>(频道中心频率之间)应有约400kHz的保护带宽，通常是由模拟B网预留。邮电部的数字移动通信系统与</SPAN></FONT></SPAN><FONT
face=楷体_GB2312 color=#000066><SPAN lang=EN-US
style="mso-ascii-font-family: 宋体">“</SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">中国联通公司</SPAN><SPAN
lang=EN-US style="mso-ascii-font-family: 宋体">”</SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">的数字移动通信系统之间也应有<SPAN
lang=EN-US>400kHz的保护带宽，即它们之间少用一个频道，或由邮电部一方预留，或由</SPAN></SPAN><SPAN
lang=EN-US style="mso-ascii-font-family: 宋体">“</SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">中国联通公司</SPAN><SPAN
lang=EN-US style="mso-ascii-font-family: 宋体">”</SPAN><SPAN
style="mso-hansi-font-family: Times New Roman">一方预留。<SPAN
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