📄 s07.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'">跳时系统虽然也是一种扩展频谱技术，但因其抗干扰性能不强，通常并不单独使用。在时分多址通信系统中利用跳时来减少网内干扰，并能改善系统中存在</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的远近效应。</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'">将跳时</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'">分别与直接扩频</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(DS)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">和跳频</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(FH)</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">相结合则构成直扩／跳时</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(DS</SPAN><SPAN
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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'">系统和跳频／跳时</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(FH</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">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'">系统。若将直扩、跳频和跳时三者结合在一起则构成直扩／跳频／跳时</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">(DS</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">FH</SPAN><SPAN
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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'">扩展频谱系统。</SPAN></P>
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lang=EN-US style="FONT-SIZE: 12pt">7.1.5<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'">混合式扩频系统的好处</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'">正如上面所列举的，每一种扩展频谱系统都有各自的长处和短处，优点和局限性。</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'">比如，当抗干扰指标要求很高时，单独的任一种扩展频谱系统往往很难达</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'">到要求，甚至遇到技术上的难题得不到解决；或者要大大增加设备的复杂程度从而使成本也大为提高。若是采用几种基本扩展频谱系统的组合，优势互补，则可满足高抗干扰指标的要求，又可能缓解某些技术难点，降低成本，从而达到更合理的性能价格比。当然，其代价是系统的复杂程度有所增加。</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'">概括而言，混合式扩展频谱系统可以带来的好处是：<SPAN
style="COLOR: teal">提高系统的抗干扰能力，降低部件制作的技术难度，使设备简化，降低成本，满足使用要求。</SPAN></SPAN><SPAN
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color=#0000cc>以下举一例来说明采用混合式扩展频谱系统的必要性。</FONT></SPAN><FONT
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face=楷体_GB2312 color=#000066>例如某系统要求扩展频谱的射频带宽应达到</FONT></SPAN><FONT
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style="FONT-SIZE: 12pt">1000MHz</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，试设计一扩展频谱系统。</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'">若采用直接序列扩展频谱系统来满足此项指标要求时，需要产生码片速率</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">500Mchip</SPAN><SPAN
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lang=EN-US style="FONT-SIZE: 12pt">s</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的伪随机序列，这在技术上是难度极大的。</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'">如果用跳频系统来实现，假设跳频频率的间隔是</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">25kHz</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">时，要求跳频器输出的跳频频率数是</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'">万个。制作跳频带宽为</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">1000MHz</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">这样的宽带和</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'">万个输出频率的跳频器在技术上也是很困难的。</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'">但是，如果采用直接序列／跳频扩展频谱系统时，直接序列的码片速率用</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">5Mchip</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">s</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，跳频器输出的跳频频率数为</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">100</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">个，最小跳频频率间隔为</SPAN><SPAN
lang=EN-US style="FONT-SIZE: 12pt">10MHz</SPAN><SPAN
style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">就可以满足要求。显然，这种混合式扩展频谱系统中的各部件的技术难度就大大降低了。</SPAN></P>
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name="7.2 几种主要的混合式扩展频谱系统">7.2<SPAN style="mso-spacerun: yes">
</SPAN></A></SPAN><A name="7.2 几种主要的混合式扩展频谱系统"><SPAN
style="FONT-SIZE: 14pt; COLOR: purple; FONT-FAMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">几种主要的混合式扩展频谱系统</SPAN><SPAN
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lang=EN-US style="FONT-SIZE: 12pt">7.2.1<SPAN
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