Noise
Noise is charcterized as random, unpredictable electrical
signals from natural sources, for example, atmospheric noise, thermal noise, shot
noise, and so on.
Because of the multiplicity of noise sources in a communications link, it is difficult to
define the properties (frequency range, level and instantaneous phase) of noise and hence
equally difficult to reduce its effect on the communications link performance. For
convenience, most textbooks and indeed practising engineers assume noise to fall
predominantly into the class of Additive White Gaussian Noise
(AWGN) which does indeed form an adequate clasification for most cases. However, we
should not forget that this is a general simplification of
the whole noise issue.
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