?? g3-2.htm
字號:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-- saved from url=(0052)http://www.mc21st.com/techfield/systech/gsm/g3-2.htm -->
<HTML><HEAD><TITLE>GSM蜂窩移動通信系統－第三講 GSM關鍵技術</TITLE><!-- #BeginTemplate "/Templates/systech-gsm.dwt" --><!-- #BeginEditable "doctitle" --><!-- #EndEditable --><LINK
href="g3-2.files/main.css" type=text/css rel=stylesheet>
<META http-equiv=Content-Type content="text/html; charset=gb2312">
<SCRIPT language=JavaScript>
<!--
function MM_reloadPage(init) { //reloads the window if Nav4 resized
if (init==true) with (navigator) {if ((appName=="Netscape")&&(parseInt(appVersion)==4)) {
document.MM_pgW=innerWidth; document.MM_pgH=innerHeight; onresize=MM_reloadPage; }}
else if (innerWidth!=document.MM_pgW || innerHeight!=document.MM_pgH) location.reload();
}
MM_reloadPage(true);
// -->
</SCRIPT>
<META content="Microsoft FrontPage 5.0" name=GENERATOR></HEAD>
<BODY bgColor=#ffffff leftMargin=2 topMargin=2>
<DIV id=Layer1
style="Z-INDEX: 1; LEFT: 671px; WIDTH: 81px; POSITION: absolute; TOP: 108px; HEIGHT: 76px"><IMG
height=77 src="g3-2.files/techspeech.gif" width=80></DIV>
<TABLE width="100%" border=0>
<TBODY>
<TR>
<TD> </TD></TR></TBODY></TABLE><!-- #BeginEditable "article" -->
<TABLE borderColor=#6666ff width="98%" align=center border=1>
<TBODY>
<TR>
<TD borderColor=#6699ff><FONT
size=2>您的位置：技術園地>技術講座-GSM蜂窩移動通信系統 </FONT></TD></TR>
<TR>
<TD borderColor=#6699ff bgColor=#ccffff>
<DIV align=center><FONT size=4><B><FONT color=#000099>第三講
GSM關鍵技術</FONT></B></FONT></DIV></TD></TR>
<TR>
<TD background=g3-2.files/bgyellow2.gif>
<DIV align=center>
<P> </P>
<TABLE cellSpacing=1 cellPadding=1 width="98%" border=0>
<TBODY>
<TR>
<TD width="12%"> </TD>
<TD width="83%">
<P style="TEXT-JUSTIFY: inter-ideograph; TEXT-ALIGN: justify"><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman"><B>3.2
時分多址技術（TDMA）<O:P> </O:P></B></SPAN></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 24pt; TEXT-ALIGN: justify; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"><SPAN
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman"><FONT
face=楷體_GB2312
color=#000066>多址技術就是要使眾多的客戶公用公共通信信道所采用的一種技術。實現多<BR>址的方法基本上有三種，即采用頻率、時間或碼元分割的多址方式，人們通常<BR>稱它們為頻分多址（<SPAN
lang=EN-US>FDMA）、時分多址（TDMA）和碼分多址（CDMA）。在傳統的無線電廣播中，均采用頻分多址（FDMA<SPAN
style="mso-spacerun: yes">
</SPAN>）方式，每個廣播信道都有一個頻點，如果你要收聽某一廣播信道，則必須把你的收音機調諧到這一頻點上。模擬蜂窩移動系統也采用了此技術，某一小區中的某一客戶呼叫占用了一個頻點，即一個信道（實際上是占用兩個，因為是雙向連接，即雙工通信），則其</SPAN>它呼叫就不能再占用。</FONT></SPAN><FONT
face=楷體_GB2312 color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman"> </SPAN></FONT><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman"><O:P>
</O:P></SPAN></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 24pt; TEXT-ALIGN: justify; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"><SPAN
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman"><FONT
face=楷體_GB2312 color=#000066>在<SPAN
lang=EN-US>GSM中，無線路徑上是采用時分多址（TDMA）方式。每一頻點（頻道或叫載頻TRX）上可分成8個時隙，每一時隙為一個信道，因此，一個TRX最多可有8個移動客戶同時使用，見圖3－6所示。<O:P>
</O:P></SPAN></FONT><FONT face=楷體_GB2312><SPAN
lang=EN-US><O:P></O:P></SPAN></FONT><FONT face=楷體_GB2312><SPAN
lang=EN-US><O:P></O:P></SPAN></FONT><SPAN
lang=EN-US><O:P></O:P></SPAN></SPAN></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 96pt; TEXT-ALIGN: justify; mso-char-indent-count: 8.0; mso-char-indent-size: 10.5pt"
align=left><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">
<IMG height=133 src="g3-2.files/g3-2.H8.gif" width=305
v:shapes="_x0000_i1025"><O:P> </O:P></SPAN></P>
<P
style="TEXT-INDENT: 24pt; TEXT-ALIGN: center; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"
align=center><SPAN
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman"><FONT
face=楷體_GB2312 color=#000066>圖<SPAN lang=EN-US>3－6
頻分多址和時分多址方式</SPAN></FONT></SPAN><FONT face=楷體_GB2312
color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman"> <O:P>
</O:P></SPAN></FONT></P>
<P
style="TEXT-INDENT: 24pt; TEXT-ALIGN: center; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"
align=center><FONT face=楷體_GB2312 color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">
<O:P></O:P></SPAN></FONT></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 24pt; TEXT-ALIGN: justify; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"><FONT
face=楷體_GB2312 color=#000066><SPAN
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">圖中所示（<SPAN
lang=EN-US>a為FDMA，b為TDMA）是一個方向的情況，在相反方向上必定有一組對應的頻率（FDMA）／時隙（TDMA）。</SPAN></SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman"> <O:P>
</O:P></SPAN></FONT></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 24pt; TEXT-ALIGN: justify; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"><FONT
face=楷體_GB2312 color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">TDMA系統具有如下特性：<O:P>
</O:P></SPAN></FONT></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 24pt; TEXT-ALIGN: justify; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"><FONT
face=楷體_GB2312 color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">(1)
每載頻多路。如前所述，TDMA系統形成頻率時間矩陣，在每一頻率上產生多個時隙，這個矩陣中的每一點都是一個信道，在基站控制分配下，可為任意一移動客戶提供電話或非話業務。 </SPAN></FONT></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 24pt; TEXT-ALIGN: justify; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"><FONT
face=楷體_GB2312 color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman; mso-char-type: symbol; mso-symbol-font-family: Wingdings; mso-ascii-font-family: 宋體"> (2)
</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">突發脈沖序列傳輸。移動臺信號功率的發射是不連續的，只是在規定的時隙內發射脈沖序列。 </SPAN></FONT></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 24pt; TEXT-ALIGN: justify; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"><FONT
face=楷體_GB2312 color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman; mso-char-type: symbol; mso-symbol-font-family: Wingdings; mso-ascii-font-family: 宋體"> (3)
</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">傳輸速率高，自適應均衡。每載頻含有時隙多，則頻率間隔寬，傳輸速率高，但數字傳輸帶來了時間色散，使時延擴展量加大，則務必采用自適應均衡技術。 </SPAN></FONT></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 24pt; TEXT-ALIGN: justify; mso-char-indent-count: 2.0; mso-char-indent-size: 10.5pt"><FONT
face=楷體_GB2312 color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman; mso-char-type: symbol; mso-symbol-font-family: Wingdings; mso-ascii-font-family: 宋體"> (4)
</SPAN><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">傳輸開銷大。由于TDMA分成時隙傳輸，使得收信機在每一突發脈沖序列上都得重新獲得同步。為了把一個時隙和另一個時隙分開，保護時間也是必須的。因此，TDMA系統通常比FDMA系統需要更多的開銷。 <O:P>
</O:P></SPAN></FONT></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 21pt; TEXT-ALIGN: justify"><FONT
face=楷體_GB2312 color=#000066>(5) <SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">對于新技術是開放的。例如當話音編碼算法的改進而降低比特速率時，TDMA系統的信道很容易重新配置以接納新技術。</SPAN></FONT></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 21pt; TEXT-ALIGN: justify"><FONT
face=楷體_GB2312 color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman; mso-char-type: symbol; mso-symbol-font-family: Wingdings; mso-ascii-font-family: 宋體">(6)</SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman">
共享設備的成本低。由于每一載頻為許多客戶提供業務，所以TDMA系統共享設備的每客戶平均成本與FDMA系統相比是大大降低了。</SPAN></FONT></P>
<P
style="TEXT-JUSTIFY: inter-ideograph; TEXT-INDENT: 21pt; TEXT-ALIGN: justify"><FONT
face=楷體_GB2312 color=#000066><SPAN lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman; mso-char-type: symbol; mso-symbol-font-family: Wingdings; mso-ascii-font-family: 宋體">(7)</SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 12pt; mso-bidi-font-size: 10.0pt; mso-hansi-font-family: Times New Roman"><SPAN
style="mso-char-type: symbol; mso-symbol-font-family: Wingdings; mso-ascii-font-family: 宋體">
</SPAN>移動臺較復雜。它比FDMA系統移動臺完成更多的功能，需要復雜的數字信號處理。</SPAN></FONT></P>
<P> </P></TD>
<TD width="5%"> </TD></TR></TBODY></TABLE>
<P> </P>
<P> </P></DIV></TD></TR>
<TR>
<TD bgColor=#ccffff>
<DIV align=center><B><a href="main.htm">目錄</a>
<a href="g3-1.htm">上一頁</a>
<a href="g3-3.htm">下一頁</a></B></DIV></TD></TR></TBODY></TABLE><!-- #EndEditable -->
<P align=center><!-- #BeginLibraryItem "/Library/close.lbi" --><A
href="javascript:window.close();">關閉窗口</A><!-- #EndLibraryItem --></P>
<TABLE width="100%" border=0>
<TBODY>
<TR>
<TD>
<DIV align=center><FONT size=2><!-- #BeginLibraryItem "/Library/copyright.lbi" --><FONT
size=2>版權所有：移動通信國家工程研究中心
2000-2001©</FONT><!-- #EndLibraryItem --></FONT></DIV></TD></TR>
<TR>
<TD>
<DIV align=center><FONT size=2></FONT><FONT size=2><!-- #BeginLibraryItem "/Library/tel.lbi" --><FONT
size=2>tel:020-84227969</FONT><!-- #EndLibraryItem --> <!-- #BeginLibraryItem "/Library/email.lbi" --><FONT
size=2><A
href="mailto:mc21stmaster@163.net">mailto:mc21stmaster@163.net</A></FONT><!-- #EndLibraryItem --></FONT></DIV></TD></TR></TBODY></TABLE>
<P> </P><!-- #EndTemplate --></BODY></HTML>?? 快捷鍵說明
復制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -