2.5  Digital Versus Analog Communication Systems

An advantage of digital over analog systems is a more efficient use of the bandwidth. Another important advantage is that, once the system is designed to transmit and receive bitstreams, any digital information can flow over the system. A good example is a wireless mobile phone system, which allows an user to send and receive text, voice, video, etc., using the same telecommunication infrastructure (physical layer).

A pertinent question is:
–If real-life channels are analog systems, why digital communication systems are becoming so popular if they require ADC and DAC chips?
The migration from analog to digital system has been done in telephony, radio and TV systems, for example.

The adoption of a finite set of symbols is typically mapped into the generation of a restricted set of waveforms, which leads to one significant advantage of a digital over an analog system: robust signal regeneration. Regeneration is a signal processing operation that recovers the original characteristics of a signal. In digital communications, this is facilitated by the fact that the system designer can assume the receiver knows the predefined set of finite symbols $M$. Application 2.1 presents an example to illustrate the concept of regeneration.

Another fact is that digital information can be more efficiently compressed to reduce the requirements for transmission or storage than what can be done in analog systems. For example, MP3 is a file extension for data generated by an audio codec that implements the standard MPEG-1 Audio Layer 3, which is very powerful. Using MP3, an uncompressed audio file can have its size decreased by a factor of more than 10 (compression ratio better than $10:1$) without noticeable degradation.

There are other good reasons for using digital signals and systems, but the mentioned four are among the most important ones:

f 1.

more efficient use of the available bandwidth;

f 2.

different media (audio, video, text, etc.) can be treated using bits, a generic representation for any information;

f 3.

efficient data compression algorithms;

f 4.

robust signal regeneration.

Application 2.1 discusses the advantage of being able to regenerate a signal in more details.