📄 s06.htm
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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'">跳频系统的特点，在很大程度上取决于它的扩展频谱机理。跳频扩展频谱在机理上与直接序列扩展频谱大不相同。从图</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'">的跳频图案上可以看出，每一</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'">跳频驻留时间的瞬时所占的信道带宽是窄带频谱，依照跳频图案随时间的变化，这些瞬时窄带频谱在一个很宽的频带内跳变，形成一个跳频带宽。由于跳频速率</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'">很快，从而在宏观上实现了频谱的扩展。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'">所示是由频谱仪上观察到的跳频信号的频谱。</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'">图中箭头所标示的，是载波频率跳变的过程。载波频率之间的频率间隔就是信道带宽，跳频的载波数目乘上信道带宽就是跳频带宽。因此，跳频系统有如下特点：</SPAN><SPAN
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color=#008080>由于它是瞬时窄带系统，它易于与目前的窄带通信系统兼容。</FONT></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'">目前的通信系统不论是模拟调制的还是数字调制的，通常都是窄带的通信系统。如果给现有的窄带通信系统加装上能使其载波频率按照某种跳频图案跳变并能实现同步接收的装置，则可改造成为跳频通信系统。</SPAN><SPAN
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style="FONT-SIZE: 12pt; COLOR: teal; FONT-FAMILY: 宋体; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">由于它是宏观的宽带系统，它具有扩展频谱的抗干扰能力。</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'">跳频扩展频谱具有抗单频干扰、多频干扰的能力，还具有抗部分频带和宽带干扰的能力。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'">给出单频干扰和部分频带干扰对跳频信号影响的示意图。</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'">所谓跳频抗干扰，是指跳频的跳频图案被敌方发现、识别的概率，以及跳频频率与敌方干扰频率相一致的概率。这种概率越小，抗干扰能力越强。</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'">表征抗多频及宽带干扰能力的跳频系统参数叫处理增益</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">G<SUB>H</SUB></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
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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'">跳频处理增益的定义是：跳频带宽内的总信道数</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'">越大，处理增益越大。但是，不能用处理增益</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'">来表征抗跟踪式干扰的能力。</SPAN><SPAN
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style="FONT-SIZE: 12pt; COLOR: teal; FONT-FAMILY: 宋体; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">由于它是按照跳频图案进行频率跳变的，它具有码分多址和频带共享的组网通信能力。</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'">组网能力是现代通信的基本要求之一。跳频通信组网可分为正交跳频网和非正交跳频网。如果多个跳频通信所采用的跳频图案在时频域“棋盘”上相互不发生重叠，则称它们为正交跳频网；如果发生重叠，则称为非正交跳频网。如图</SPAN><SPAN
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根据跳频网的同步方式，可分为同步网和异步网。正交跳频网为了保证跳频图案的正交，要求全网严格的定时，采用同步网方式，所以它是正交跳频同步网。由于正交网的跳频图案不发生重叠，所以它不存在因跳频频率重合引起的网间⌨️ 快捷键说明
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