Basics of Digital
Communication
A communication system's goal is to produce data-carrying
signals from a source in one location to a user destination in another.
Communication systems may be classified into two categories based on the type
of signal processing used on the information-carrying signal. They are:
1) Analog
Communication System
2) Digital
Communication System
The information-carrying analog signal in an analog
communication system is constantly changing in both amplitude and time. It is
directly used to change the amplitude, phase, or frequency of a high-frequency
sinusoidal carrier wave. Analog signals include speech, video, temperature, and
pressure signals, among others.
The information-carrying digital signal is processed in a
digital communication system so that it may be represented by a series of
binary digits (discrete messages). Then it's used to toggle between ON and OFF
any aspect of a high-frequency sinusoidal carrier wave, such as amplitude,
phase, or frequency. If the input message signal is analog, sampling, quantizing,
and encoding are used to transform it to digital form. Digital signals include
computer data and telegraph signals. A digital communication system's most
distinguishing feature is that it works with a limited number of distinct
messages.
Due to the ever-increasing demand for data communication, digital communication technologies are becoming more appealing. Because digital transmission provides data processing choices and flexibility that analog transmission does not. Furthermore, advances in digital technology have resulted in the creation of increasingly powerful microprocessors, larger and larger memory devices, and a growing number of programmable logic devices. Due to the widespread availability of these devices, designing digital communication networks has become much easier.
DIGITAL COMMUNICATION SIGNAL PROCESSING
Information (speech, video, or data) is transmitted along a
path (channel) made up of wires, waveguides, or space. A digital communication
system's main characteristic is that it delivers a signal waveform from a
finite set of potential waveforms over a fixed period. The amplitude and shape
of the signal waveform deteriorate throughout propagation. The receiver's goal
is to figure out which waveform from a finite number of waveforms was delivered
by the transmitter from a noise-perturbed signal.
An ideal binary digital pulse traveling through a
transmission wire is shown in the figure. Two fundamental mechanisms influence
the waveform's shape.
1) All transmission lines and circuits have a non-ideal
frequency transfer function.
2) Electrical noise or other interference alters the pulse
waveform much more.
As shown in the figure, both of these methods lead the pulse form to degrade as a function of line length.
The pulse is increased by a digital amplifier in Regeneration, which restores its original perfect form. As a result, the pulse is "reborn" or "regenerated." Regenerative repeaters are circuits that execute this function at regular intervals throughout a transmission system.