Q. What do you mean by Noise?

In any communication system there are usually two dominant factors that limit the performance of the system:

1. Additive noise, generated by electronic devices that are used to filter and amplify the communication signal.

2. Signal attenuation, as the signal travels through a lossy channel. A simple mathematical model of a channel with attenuation and additive noise is shown in Figure. If the transmitted signal is s(t), the received signal is given by

r(t) = αs(t) + n(t)

where α < 1, and n(t) represents an additive random noise process corrupting the transmitted signal. Physically, the additive noise may arise from electronic components and amplifiers at the receiver of the communication system, or from interference encountered in transmission as in the case of radio-signal transmission. The effect of signal attenuation is to reduce the amplitude of the desired signal s(t) and, thus, to render the information-bearing signal more vulnerable to additive noise.

Signal attenuation in many channels can be offset by using amplifiers to boost the signal level during transmission. However, the amplifier also introduces additive noise in the process of amplification, thereby corrupting the signal. The additional noise must also be taken into consideration in the design of the communication system.