s04.htm

扩频通信讲座

            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">    
            总之，跳频系统占用了比信息带宽要宽得多的频带。</SPAN></P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%"><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><B><FONT color=#0080c0><A 
            name="4.2.3  跳变时间(Time Hopping)工作方式，简称跳时(TH)方式">4.2.3<SPAN 
            style="mso-spacerun: yes">&nbsp; 
            </SPAN></A></FONT></B></SPAN><B><FONT color=#0080c0><A 
            name="4.2.3  跳变时间(Time Hopping)工作方式，简称跳时(TH)方式"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">跳变时间</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(Time Hopping)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">工作方式，简称跳时</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(TH)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">方式</SPAN></A></FONT></B></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">与跳频相似，跳时</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(TH</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">Time Hopping)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是使发射信号在时间轴上跳变。首先把时间轴分成许多时片。在一帧内哪个时片发射信号由扩频码序列去进行控制。可以把跳时理解为：用一定码序列进行选择的多时片的时移键控。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">由于采用了窄得很多的时片去发送信号，相对说来，</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">信号的频谱也就展宽了。图</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">4</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">3</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是跳时系统的原理方框图。在发端，输入的数据先存储起来，由扩频码发生器的扩频码序列去控制通－断开关，经二相或四相调制后再经射频调制后发射。在收端，由射频接收机输出的中频信号经本地产生的与发端相同的扩频码序列控制通－断开关，再经二相或四相解调器，送到数据存储器和再定时后输出数据。只要收发两端在时间上严格同步进行，就能正确地恢复原始数据。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">&nbsp;</SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt" 
            align=center><IMG height=307 src="s04.files/b4.gif" width=450 
            border=0><SPAN lang=EN-US style="FONT-SIZE: 12pt"><O:P> 
            </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; TEXT-ALIGN: center; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt" 
            align=center><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">图</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">4</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">3<SPAN 
            style="mso-spacerun: yes">&nbsp; </SPAN>(a),<SPAN 
            style="mso-spacerun: yes">&nbsp; </SPAN>(b)&nbsp;</SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; TEXT-ALIGN: center; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt" 
            align=center><SPAN lang=EN-US 
            style="FONT-SIZE: 12pt"><O:P></O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">跳时也可以看成是一种时分系统，所不的地方在于它不是在一帧中固定分配一定位置的时片，而是由扩频码序列控制的按一定规律跳变位置的时片。跳时系统的处理增益等于一帧中所分的时片数。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">由于简单的跳时抗于拢性不强，很少单独使用。跳时通常都与其他方式结合使用，组成各种混合方式。</SPAN><B><FONT 
            color=#0080c0><SPAN lang=EN-US style="FONT-SIZE: 12pt"><O:P> 
            </O:P></SPAN></FONT></B></P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%"><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><B><FONT color=#0080c0><A 
            name="4.2.4  宽带线性调频(Chirp Modulation)工作方式，简称Chirp方式">4.2.4<SPAN 
            style="mso-spacerun: yes">&nbsp; 
            </SPAN></A></FONT></B></SPAN><B><FONT color=#0080c0><A 
            name="4.2.4  宽带线性调频(Chirp Modulation)工作方式，简称Chirp方式"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">宽带线性调频</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(Chirp Modulation)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">工作方式，简称</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">Chirp</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">方式</SPAN></A></FONT></B></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">如果发射的射频脉冲信号在一个周期内，其载频的频率作线性变化，则称为线性调频。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">因为其频率在较宽的领带内变化，信号的频带也被展宽了。这种扩频调制方式主要用在雷达中，但在通信中也有应用。图</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">4</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">4</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是线性调频的示意图。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt" 
            align=center><SPAN lang=EN-US style="FONT-SIZE: 12pt"><IMG 
            height=156 src="s04.files/b5.gif" width=600 border=0>&nbsp;<O:P> 
            </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; TEXT-ALIGN: center; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt" 
            align=center><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">图</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">4</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">4<O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">发端有一锯齿波去调制压控振荡器，从而产生线性调频脉冲。它和扫频信号发生器产生的信号一样。</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在收端，线性调频脉冲由匹配滤波器对其进行压缩，把能量集中在一个很短的时间内输出，从而提高了信噪比，获得了处理增益。匹配滤波器可采用色散延迟线，它是一个存储和累加器件。其作用机理是对不同频率的延迟时间不一样。如果使脉冲前后两端的频率经不同的延迟后一同输出，则匹配滤波器起到了脉冲压缩和能量集中的作用。匹配滤波器输出信噪比的改善是脉冲宽度与调频频偏乘积的函数。一般，线性调频在通信中很少应用。</SPAN><B><FONT 
            color=#0080c0><SPAN lang=EN-US style="FONT-SIZE: 12pt"> 
            </SPAN></FONT></B></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><B><FONT 
            color=#0080c0><SPAN lang=EN-US 
            style="FONT-SIZE: 12pt"></SPAN></FONT></B></P>
            <P class=MsoNormal 
            style="MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px; LINE-HEIGHT: 150%"><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt"><B><FONT color=#0080c0><A 
            name="4.2.5  各种混合方式">4.2.5<SPAN style="mso-spacerun: yes">&nbsp; 
            </SPAN></A></FONT></B></SPAN><B><FONT color=#0080c0><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><A 
            name="4.2.5  各种混合方式">各种混合方式</A></SPAN></FONT></B></P>
            <P class=MsoNormal 
            style="TEXT-INDENT: 24pt; LINE-HEIGHT: 150%; mso-char-indent-count: 2.0; mso-char-indent-size: 12.0pt"><SPAN