Q.Why is digital communication preferred?

In digital communication, information is encoded as discrete (digital) signals — sequences of 1s and 0s — and transferred electronically to the recipient. It is one of the commonest modes of communication today: the source is often simply a computer keyboard, a single person can operate it, and it is among the cheapest, fastest and most reliable modes, delivering a message in a fraction of a second.

Analog and digital communication differ in several ways. An analog signal varies continuously through infinitely many values and uses modulation schemes such as AM, FM, PAM and PWM; its circuitry is simpler and needs less bandwidth, but it is slower, noisier and less efficient. A digital signal takes only a finite set of discrete values and uses schemes such as PCM; its circuitry is more complex and needs larger bandwidth, but it is faster, far less noisy and more efficient — which is why digital communication is generally preferred.

A digital communication system passes the signal through the following blocks:

Information input → Source encoder → Channel encoder → Modulator → Channel → Detector → Channel decoder → Source decoder → Information output.

• Source encoder — converts the information into binary code (digitising an analog input if necessary). …