Definition:-                     

                        Noise is an unwanted signal which interferes with the original message signal and corrupts the parameters of the message signal. This alteration in the communication process, leads to the message getting altered. It is most likely to be entered at the channel or the receiver.

                     

Hence, it is understood that noise is some signal which has no pattern and no constant frequency or amplitude. It is quite random and unpredictable. Measures are usually taken to reduce it, though it can’t be completely eliminated.

Effects of Noise:

Noise is an inconvenient feature which affects the system performance. Following are the effects of noise:

1.Noise limits the operating range of the systems

2.Noise affects the sensitivity of receivers

Types of Noise:

The classification of noise is done depending on the type of the source, the effect it shows or the relation it has with the receiver, etc.

There are two main ways in which noise is produced. One is through some external source while the other is created by an internal source, within the receiver section.

External Source

This noise is produced by the external sources which may occur in the medium or channel of communication, usually. This noise cannot be completely eliminated. The best way is to avoid the noise from affecting the signal.

Examples:

Atmospheric noise (due to irregularities in the atmosphere).

Extra-terrestrial noise, such as solar noise and cosmic noise. Industrial noise.

Internal Source

This noise is produced by the receiver components while functioning. The components in the circuits, due to continuous functioning, may produce few types of noise. This noise is quantifiable. A proper receiver design may lower the effect of this internal noise. 

Examples

•Thermal agitation noise (Johnson noise or Electrical noise).

•Shot noise (due to the random movement of electrons and holes).

•Transit-time noise (during transition).

•Miscellaneous noise is another type of noise which includes flicker, resistance effect and mixer generated noise, etc.