s06-03.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'">数字跳频系统是指传送数字话音或数据的跳频通信系统。因此，它传送跳频同步信息是以数据帧的格式进行的。数字系统跳频同步方法也不外乎同步字头法，自同步法和参考时钟法。</SPAN><SPAN 
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            </SPAN><SPAN 
            style="FONT-SIZE: 11pt; COLOR: blue; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-bidi-font-size: 12.0pt">同步字头法。</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">发端需发送含有同步信息的码字，收端解码后，依据同步信息使收端本地跳频器与发端同步。同步信息除位同步、帧同步外，主要应包括跳频图案的实时状态信息或实时的时钟信息，即所谓的“</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">TOD</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">”信息</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">(Time of the Day)</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。实时时钟信息包括年月日时分秒，毫秒、微秒、毫微秒等；状态信息是指伪码发生器实时的码序列状态。根据这些信息，收端就可以知道当前跳频驻留时间的频率和下一跳驻留时间应当处在什么频率上，从而使收发端跳频器同步工作。为了</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">保证</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">信息的正确接收，在如图</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">所示的同步信息数据帧格式中装有位同步和帧同步位。此外，对</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">信息位可采用差错控制技术，如纠错编码，相关编码或采用大数判决，以提高传输的可靠性。</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; mso-spacerun: yes">&nbsp;&nbsp;&nbsp; 
            </SPAN><SPAN 
            style="FONT-SIZE: 11pt; COLOR: blue; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-bidi-font-size: 12.0pt">参考时钟法。</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在一个通信网内，设一个中心站，它播发高精度的时钟信息，所有网内的用户依照此标准时钟来控制收、发信机的同步定时，达到收、发双方同步。采用这种方法进行跳频同步，需要事先约定好所采用的跳频图案和频率表，或者，需通过其它方式将跳频图案情息通知网内用户。此法需要一个精度极高的标准时钟，否则不能实现跳频通信。</SPAN><SPAN 
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            </SPAN><SPAN 
            style="FONT-SIZE: 11pt; COLOR: blue; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-bidi-font-size: 12.0pt">自同步法。</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">它是依靠从接收到的跳频信号中提取有关同步信息来实现跳频同步的。</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">数字跳频系统中，根据需要也可采用不同方法的组合。比如，自同步法具有同步信息隐蔽的优点，但是存在同步建立时间长的缺点；而同步字头法具有快速</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">建立同步的优点而存在同步信息不够隐蔽的缺点。因此可将这两种方法进行组合，得到一个综合最佳的同步系统。图</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">所示的是等待自同步法的跳频同步</SPAN><SPAN 
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            </SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">过程。</SPAN><SPAN 
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            align=center><SPAN lang=EN-US style="FONT-SIZE: 12pt">&nbsp;<IMG 
            height=380 src="s06-03.files/s6-12.gif" width=500 border=0><O:P> 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">图中，接收端在频率</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">f6</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">上等待接收跳频信号；发送端发送的跳频信号的载波频率依次在</SPAN><SPAN 
            lang=EN-US style="FONT-SIZE: 12pt">f5</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">f1</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">f3</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">f4</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">f2</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">f6 …</SPAN><SPAN 
            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">上跳变。当发端信号的载频跳变至</SPAN><SPAN 
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            style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">时，收端接收到跳频信号，这时称作同步捕获，即可从跳频信号中解出它所携带的同步字头内的同步信息。接着，就依照同步信息的指令开始同步跳频，即由等待阶段转入同步跳频的阶段，从而建立了跳频系统的同步。</SPAN></P>
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            lang=EN-US style="FONT-SIZE: 12pt; COLOR: navy">6.3.3<SPAN 
            style="mso-spacerun: yes">&nbsp; </SPAN></SPAN><SPAN 
            style="FONT-SIZE: 12pt; COLOR: navy; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">跳频同步系统性能及抗干扰性</SPAN><SPAN 
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