## Sources of link degradation (cont. 3)

### 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. |