digital transmission provides a powerful method for overcoming noisy environments.
数字传输对于克服噪声环境的影响提供了一个强有力的手段(method方法)
noise can be introduced into transmission path in many different ways; perhaps via anearbylightning strike,the sparking of a car ignition system, orthe thermal low-levelnoisewithin the communication equipment itself.
sparking of a car ignition system?
汽车点火系统的打火。
thermal low-level noise?
低电平的热噪声。
噪声可以以多种不同的方式进入传输信道,比如说因为附近的闪电、汽车点火系统的打火或因通信设备本身低电平热噪声所致。
it is the relationship of the true signal to the noise signal,known as
the signal-to-noiseratiowhichis of the most interest to
the communication engineer.
正是这种被称为信噪比的即真实信号与噪声的关系引起了通信工程师的极大的兴趣。
basically, if the signal is very large compared to the noise level, then a perfect messagecan take place; however,this is not always the case.
this is not always the case
实际情况并非如此.
从本质上讲,如果信号比噪声电平大得多,则信息的传输是完美的。但是,实际情况并不总是这样。
for example, the signal received from a satellite,located in far outer space,is very weakand is at a level only slightly above that of the noise.
例如,从位于遥远太空中的卫星接收的信号极其微弱,其电平仅比噪声稍高一点。
alternative examplesmay be found within terrestrial systems
where, although themessage signal is strong, so is the noise power.
地面系统则是另一类例子,尽管信号很强,噪声也很强。
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