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<TD borderColor=#6699ff><FONT
size=2>您的位置：技术园地>技术讲座-GSM蜂窝移动通信系统 </FONT></TD></TR>
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<DIV align=center><FONT size=4><B><FONT color=#000099>第三讲
GSM关键技术</FONT></B></FONT></DIV></TD></TR>
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style="FONT-SIZE: 10pt; FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'"><B>3.9<SPAN
style="mso-spacerun: yes"> </SPAN></B></SPAN><B><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'">交织技术<SPAN
lang=EN-US><O:P></O:P></SPAN></SPAN></B></P>
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style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><O:P></O:P></SPAN></SPAN></B></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>在陆地移动通信这种变参信道上，比特差错经常是成串发生的。这是由于持<BR>续较长的深衰落谷点会影响到相继一串的比特。然而，信道编码仅在检测和<BR>校正单个差错和不太长的差错串时才有效。为了解决这一问题，希望能找到<BR>把一条消息中的相继比特分散开的方法，即一条消息中的相继比特以非相继方式被发送。这样，在传输过程中即使发生了成串差错，恢复成一条相继比特串的消息时，差错也就变成单个<SPAN
lang=EN-US>(或长度很短)，这时再用信道编码纠错功能纠正差错，恢复原消息。这种方法就是交织技术。</SPAN></FONT><FONT
size=3><SPAN lang=EN-US><O:P> </O:P></SPAN></FONT></SPAN></P>
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style="MARGIN-TOP: 0px; TEXT-JUSTIFY: inter-ideograph; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21pt; TEXT-ALIGN: justify"><SPAN
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style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'"><FONT
size=3> <O:P> </O:P></FONT></SPAN></P>
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</SPAN><FONT color=#0000cc>1．交织技术的一般原理<O:P>
</O:P></FONT><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>假定由一些<SPAN
lang=EN-US>4比特组成的消息分组，把4个相继分组中的第1个比特取出来，并让这4个第1比特组成一个新的4比特分组，称作第一帧，4个消息分组中的比特2～4，也作同样处理，如图3-30所示。</SPAN></FONT><FONT
size=3><SPAN lang=EN-US><O:P> </O:P></SPAN></FONT></SPAN></P>
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</SPAN><FONT face=楷体_GB2312
color=#000066>然后依次传送第1比特组成的帧，第2比特组成的帧，……。在传输期间，帧2丢失，如果没有交织，那就会丢失某一整个消息分组，但采用了交织，仅每个消息分组的第2比特丢失，再利用信道编码，
全部分组中的消息仍能得以恢复，这就是交织技术的基本原理。概括地说，交织就是把码字的b个比特分散到n个帧中，以改变比特间的邻近关系，因此n值越大，传输特性越好，但传输时延也越大，所以在实际使用中必须作折衷考虑。</FONT></FONT></SPAN></P>
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size=3><FONT face=楷体_GB2312
color=#000066><O:P></O:P></FONT></FONT></SPAN></P>
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align=center><SPAN lang=EN-US
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size=3> <IMG height=112
src="g3-9.files/g3-9.H7.gif" width=378 v:shapes="_x0000_i1025"><O:P>
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face=楷体_GB2312 color=#000066 size=3>图<SPAN lang=EN-US>3-30 交织原理<O:P>
</O:P></SPAN></FONT></SPAN></P>
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align=center><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'"><FONT
size=3><SPAN lang=EN-US><O:P></O:P></SPAN></FONT></SPAN></P>
<P class=MsoNormal
style="MARGIN-TOP: 0px; TEXT-JUSTIFY: inter-ideograph; MARGIN-BOTTOM: 0px; TEXT-ALIGN: justify"><SPAN
lang=EN-US
style="FONT-FAMILY: 宋体; mso-hansi-font-family: 'Times New Roman'"><FONT
size=3><SPAN
style="FONT-FAMILY: 宋体; mso-hansi-font-family: Times New Roman; mso-spacerun: yes">
</SPAN><O:P></O:P></FONT></SPAN></P>
<P class=MsoNormal
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lang=EN-US
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size=3><SPAN
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</SPAN><FONT color=#0000cc>2．GSM系统中交织方式<O:P>
</O:P></FONT></FONT></SPAN></P>
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lang=EN-US
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size=3><SPAN
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</SPAN><FONT face=楷体_GB2312
color=#000066>在GSM系统中，信道编码后进行交织，交织分为两次，第一次交织为内部交织，第二次交织为块间交织。</FONT><O:P>
</O:P></FONT></SPAN></P>
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