The term noise is used to designate unwanted waves that tend to disturb the transmission and processing of signals in communication systems and over which we have incomplete control.
"Noise may also be defined as an extraneous form of energy with random frequency and amplitude which tends to interfere with reception of a signal from a distant station."
Classification of noise:
In general, noise may be picked up by a signal during transmission from a transmitter to a receiver. Such a type of noise is commonly termed as external noise Alternatively, noise may be produced within receiving equipment while it is receiving a signal. This type of noise is called as inter noise. The source of noise may be external or internal to the system.
Correlated noise:
Correlated noise is a noise that is correlated to the signal and cannot be present in a circuit unless there is an input signal. It is produced by non-linear amplification of non-linear devices such as diodes.
Uncorrelated noise:
Uncorrelated noise is present regardless of whether there is a signal present or not. It is of two types
- External noise
- Internal noise
External noise:
The noise may be picked or added up by a signal during its transmission from a transmitter to a receiver. Such type of noise is known as external noise. It is of two types.- Atmospheric noise
- Man-made noise
Internal noise:
Internal noise arises from spontaneous fluctuation of current or voltage in electrical circuits. They represent a basic limitation on the transmission or detection of signals in the communication system involving the use of electronic devices. The inter noise in classified into three types.
- Shot noise
- Thermal noise
- White noise