Noise is a third impairment. It can be define as an unwanted energy from sources other than the transmitter.
- Thermal noise is caused by the random motion of the electrons in a wire and is unavoidable.
- In communication systems too, noise is an error or undesired random disturbance of a useful information signal in a communication channel.
- Image noise is random variation of brightness or color information in images, and is usually an aspect of electronic noise. It can be produced by the sensor and circuitry of a scanner or digital camera.
The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources.
There are two important characteristics of sound or noise – frequency and loudness. At the receiver, the signal is recovered from the received signal that is signals are reconstructed by sampling. Increased data rate implies “shorter” bits with higher sensitivity to noise.