lang=EN-US 
            style="FONT-SIZE: 12pt; mso-spacerun: yes">    
            </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">擴(kuò)頻通信提高了抗干擾性能，但付出了占用頻帶寬的代價(jià)。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">&nbsp;&nbsp;&nbsp; 
            </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">如果讓許多用戶共用這一寬頻帶，則可大為提高頻帶的利用率。由于在擴(kuò)頻通信中存在擴(kuò)頻碼序列的擴(kuò)頻調(diào)制，充分利用各種不同碼型的擴(kuò)頻碼序列之間優(yōu)良的自相關(guān)特性和互相關(guān)特性，在接收端利用相關(guān)檢測(cè)技術(shù)進(jìn)行解擴(kuò)，則在分配給不同用戶碼型的情況下可以區(qū)分不同用戶的信號(hào)，提取出有用信號(hào)。這樣一來(lái)，在一寬頻帶上許多對(duì)用戶可以同時(shí)通話而互不干擾。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%">　</P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%"><SPAN 
            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%"><FONT 
            size=4><A name="3.5  抗多徑干擾"><B><FONT color=#800080><SPAN 
            lang=EN-US>3.5<SPAN style="mso-spacerun: yes">&nbsp; 
            </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋體; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">抗多徑干擾</SPAN></FONT></B></A></FONT><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: 12pt; LINE-HEIGHT: 150%; mso-char-indent-count: 1.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在無(wú)線通信的各個(gè)頻段，長(zhǎng)期以來(lái)，多徑干擾始終是一個(gè)難以解決的問(wèn)題之一。在以往的窄帶通信中，采用兩種方法來(lái)提高抗多徑干擾的能力：</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: 12pt; LINE-HEIGHT: 150%; mso-char-indent-count: 1.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">一是把最強(qiáng)的有用信號(hào)分離出來(lái)，排除其他路徑的干擾信號(hào)，即采用分集／</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">接收技術(shù)；</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: 12pt; LINE-HEIGHT: 150%; mso-char-indent-count: 1.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">二是設(shè)法把不同路徑來(lái)的不同延遲、不同相位的倍號(hào)在接收端從時(shí)域上對(duì)齊</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">相加，合并成較強(qiáng)的有用信號(hào)，即采用梳狀濾波器的方法。</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: 12pt; LINE-HEIGHT: 150%; mso-char-indent-count: 1.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">這兩種技術(shù)在擴(kuò)頻通信中都易于實(shí)現(xiàn)。利用擴(kuò)頻碼的自相關(guān)特性，在接收端</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt; mso-spacerun: yes"> </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">從多徑信號(hào)中提取和分離出最強(qiáng)的有用信號(hào)，或把多個(gè)路徑來(lái)的同一碼序列的波形相加合成，這相當(dāng)于梳狀濾波器的作用。另外，采用頻率跳變擴(kuò)頻調(diào)制方式的擴(kuò)頻系統(tǒng)中，由于用多個(gè)頻率的信號(hào)傳送同一個(gè)信息，實(shí)際上起到了頻率分集的作用。</SPAN></P>
            <P>　</P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 12pt; LINE-HEIGHT: 150%; mso-char-indent-count: 1.0; mso-char-indent-size: 12.0pt"></P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 12pt; LINE-HEIGHT: 150%; mso-char-indent-count: 1.0; mso-char-indent-size: 12.0pt"><SPAN 
            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%"><FONT 
            size=4><A name="3.6  能精確地定時(shí)和測(cè)距"><B><FONT color=#800080><SPAN 
            lang=EN-US>3.6<SPAN style="mso-spacerun: yes">&nbsp; 
            </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋體; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">能精確地定時(shí)和測(cè)距</SPAN></FONT></B></A></FONT><SPAN 
            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%"><SPAN 
            lang=EN-US 
            style="FONT-SIZE: 12pt; mso-spacerun: yes">&nbsp;&nbsp;&nbsp; 
            </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">我們知道電磁波在空間的傳播速度是固定不變的光速。人們自然會(huì)想到如果能夠精確測(cè)量電磁波在兩個(gè)物體之間傳播的時(shí)間，也就等于測(cè)量?jī)蓚€(gè)物體之間的距離。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">&nbsp;&nbsp;&nbsp; 
            </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在擴(kuò)頻通信中如果擴(kuò)展頻譜很寬，則意味著所采用的擴(kuò)頻碼速率很高，每個(gè)碼片占用的時(shí)間就很短。當(dāng)發(fā)射出去的擴(kuò)頻信號(hào)在被測(cè)物體反射回來(lái)后，在接收端解調(diào)出擴(kuò)頻碼序列，然后比較收發(fā)兩個(gè)碼序列相位之差，就可以精確測(cè)出擴(kuò)頻信號(hào)往返的時(shí)間差，從而算出二者之間的距離。測(cè)量的精度決定于碼片的寬度，也就是擴(kuò)展頻譜的寬度。碼片越窄，擴(kuò)展的頻譜越寬，精度越高。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%">　</P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%"><SPAN 
            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%"><FONT 
            size=4><A name="3.7  適合數(shù)字話音和數(shù)據(jù)傳輸，以及開(kāi)展多種通信業(yè)務(wù)"><B><FONT 
            color=#800080><SPAN lang=EN-US>3.7<SPAN 
            style="mso-spacerun: yes">&nbsp; </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋體; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">適合數(shù)字話音和數(shù)據(jù)傳輸，以及開(kāi)展多種通信業(yè)務(wù)</SPAN></FONT></B></A></FONT><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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">擴(kuò)頻通信一般都采用數(shù)字通信、碼分多址技術(shù)，適用于計(jì)算機(jī)網(wǎng)絡(luò)，適合于數(shù)據(jù)和圖象傳輸。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21.75pt; LINE-HEIGHT: 150%">　</P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; TEXT-INDENT: 21.75pt; LINE-HEIGHT: 150%"><SPAN 
            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%"><FONT 
            size=4><A name="3.8  安裝簡(jiǎn)便，易于維護(hù)"><B><FONT color=#800080><SPAN 
            lang=EN-US>3.8<SPAN style="mso-spacerun: yes">&nbsp; 
            </SPAN></SPAN><SPAN 
            style="FONT-FAMILY: 宋體; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">安裝簡(jiǎn)便，易于維護(hù)</SPAN></FONT></B></A></FONT><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: 宋體; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">擴(kuò)頻通信設(shè)備是高度集成，采用了現(xiàn)代電子科技的尖端技術(shù)，因此，十分可靠、小巧，大量運(yùn)用后成本低，安裝便捷，易于推廣應(yīng)用。</SPAN></P></TD>
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