1. Woldia University
Institute of Technology
School of Electrical and Computer
Engineering
Chapter One
Introduction to Electronic Communication
Systems
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3. Introduction
Elements of Communication Systems
Classification of Communication Systems
Outline
1 Introduction
2 Elements of Communication Systems
3 Classification of Communication Systems
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4. Introduction
Elements of Communication Systems
Classification of Communication Systems
Introduction to Electronic communication
A communication system can be broadly defined as the transfer of
information signals from a source, located at one point in space, to
a user destination, located at another point
It could be over short or long distances, out of which
communication at a distance is known as telecommunication
In today’s world, there are number of modern communication
systems in use, which may include radio telephony and telegraph,
broadcasting (both radio and television), point to point and mobile
communication, radio telemetry, internet and so on.
In order to become familiar with these communication systems, it
is necessary to understand the basic building blocks of
communication systems, the concept of noise, modulation,
multiplexing, and various other systems.
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5. Introduction
Elements of Communication Systems
Classification of Communication Systems
Elements of Communication Systems
As shown in figure 1 below, any communication system consists of
basic elements such as, information source, input transducer,
transmitter block, communication channel/medium, receiver block,
output transducer and information sink/destination.
The source originates a message, such as a human voice, a
television picture, a computer text message, or data.
If the data is non-electrical (human voice, teletype message,
television picture), it must be converted by an input
transducer into an electrical waveform referred to as the
baseband signal or message signal.
Figure 1: Basic parts of communication system
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6. Introduction
Elements of Communication Systems
Classification of Communication Systems
Transmittere
Transmitter
The main purpose of the transmitter is to modify the message
signal into a form suitable for transmission over the channel.
It may involve signal processing techniques such as,
multiplexing, modulation, encoding and amplification.
Modulation is a process of mixing the message signal with a
very high frequency carrier, which is suitable for propagation.
Multiplexing is also another process that allows two or more
signals to share the same medium or channel.
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7. Introduction
Elements of Communication Systems
Classification of Communication Systems
Communication Channel
Is the medium by which the electronic signal is sent from one
place to another. Many different types of media are used in
communication systems, including wire conductors, fiber-optic
cable, and free space.
Various unwanted and undesirable effects crop up in the course of
signal transmission.
Attenuation is undesirable since it reduces signal strength at
the receiver.
More serious, however, are distortion, interference, and noise,
which appear as alterations of the signal shape.
Although such contamination may occur at any point, the
standard convention is to blame them entirely on the channel,
treating the transmitter and receiver as being ideal.
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8. Introduction
Elements of Communication Systems
Classification of Communication Systems
Noise refers to random and unpredictable electrical signals
produced by natural processes both internal and external to
the system.
Filtering reduces noise contamination, but there inevitably
remains some amount of noise that cannot be eliminated.
This noise constitutes one of the fundamental system
limitations.
Interference is contamination by extraneous signals from
human sources, other transmitters, power lines and machinery,
switching circuits, and so on.
Distortion Distortion is waveform perturbation caused by
imperfect response of the system to the desired signal itself.
Unlike noise and interference, distortion disappears when the
signal is turned off.
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9. Introduction
Elements of Communication Systems
Classification of Communication Systems
Receiver
The main purpose of the receiver is to reproduce the original
message signal from the degraded version of the transmitted
signal after propagation through the channel.
This is accomplished by using a process of demodulation and
amplification.
Demodulation is a reverse of modulation. It is a process of
extracting the original message from the received signal.or
Output Transducer
This device converts the electric signal at its input into the
form desired by the system user.
Perhaps the most common output transducers may include a
loudspeaker or ear phone, monitor, etc.
The destination is the unit to which the message is
communicated.
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10. Introduction
Elements of Communication Systems
Classification of Communication Systems
Classification of Communication Systems
There are three ways in which communication systems are
classified: analog or digital systems, one-way (simplex) or two-way
(half full duplex) systems, and base band or modulated systems.
According to the message signal communicated, communication
systems can be classified in to two types: Analog and Digital.
Analog communication system is the one in which message
signal is transmitted and received in analog form.
Digital communication systems are systems in which message
signal is transmitted and received in digital form.
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11. Introduction
Elements of Communication Systems
Classification of Communication Systems
Analog Communication System
Figure 2: Typical Block diagram of Analog communication Systems
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12. Introduction
Elements of Communication Systems
Classification of Communication Systems
Digital Communication System
Figure 3: Typical Block diagram of digital Communication Systems
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13. Introduction
Elements of Communication Systems
Classification of Communication Systems
Comparison of Digital and Analog communication Systems
Digital communication has a number of advantages
Relatively inexpensive digital circuits can be used
Privacy is preserved by using data encryption
Greater dynamic range is possible
Data from voice, video, and data sources can be merged and
transmitted over a common digital transmission system.
In long distance systems, noise does not accumulate from
repeater to repeater.
Errors in detected data are small, even when there is a large
amount of noise on the received signal.
Errors can often be corrected by the use of coding
Digital communication also has disadvantages
Generally more bandwidth is required than that for analog
systems.
Synchronization between the transmitter and receiver is
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14. Introduction
Elements of Communication Systems
Classification of Communication Systems
Base Band Transmission
In a communication system, the original information signal
(baseband signals) could be transmitted over the medium.
Putting the original signal directly into the medium is referred
to as baseband transmission.
Limitations of Baseband Transmission
There are many instances when the baseband signals are
incompatible for direct transmission over the communication
medium.
Although it is theoretically possible to transmit voice signals
directly by radio, realistically it is impractical.
For example, voice signals can’t travel longer distances in air
as they get attenuated rapidly.
Hence to overcome the limitations of baseband transmission,
modulation techniques has to be used.
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15. Introduction
Elements of Communication Systems
Classification of Communication Systems
Modulation Techniques
In modulation process, the baseband signal (such as voice,
video, etc.) modifies another higherfrequency signal called
carrier which is usally a sinusoidal wave that is higher in
frequency than the highest baseband signal frequency.
The baseband signal modifies the amplitude or frequency or
phase of the carrier in the modulation process.
Need for Modulation We have seen that baseband signals are
incompatible for direct transmission over the medium and therfore
we have to use modulation techniques for the communication of
baseband signal.
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16. Introduction
Elements of Communication Systems
Classification of Communication Systems
The advantages of using modulation technique are as given below;
Reduce the height of antenna
Avoids mixing of signals
Increase the range of communication
Allows multiplexing of signals
Allows adjustments in the bandwidth
Modulation Types There are many modulation and demodulation
techniques;
Continuous wave modulation- DSB, DSB-SC, SSB, VSB, FM,
PM
Pulse modulation- PAM, PWM, PPM, PCM, DPCM, DM
Digital modulation- ASK, FSK, PSK, QAM
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17. Introduction
Elements of Communication Systems
Classification of Communication Systems
Fundamental Limitations of Communication Systems
The goal of a communication system engineer is to design
systems that provide high quality service for the maximum
number of user with the smallest cost and least usage of
limited resources.
Communication systems face fundamental limitations such as
noise, distortion and bandwidth which determine the
performance each system.
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18. Introduction
Elements of Communication Systems
Classification of Communication Systems
Signal Distortion in Transmission
A signal transmission medium is the electrical channel
between an information source and destination.
These systems range in complexity from a simple pair of wires
to a sophisticated laseroptics links
Distortion-less Transmission
Distortion-less transmission means that the output signal has
the same shape as the input.
More precisely, given an input signal x(t) we say that the
output is undistorted if it differs from the input by a
multiplying constant and a finite time delay.
Analytically, we have distortion-less transmission if its output is
related to its input as;
y(t) = Kx(t − td ) (1)
Where K and td are constants.
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19. Introduction
Elements of Communication Systems
Classification of Communication Systems
For the purpose of studying distortion effects on various
signals, we’ll define three major types of distortion:
The first two types can be grouped under the general
designation of linear distortion, described in terms of the
transfer function of a linear system.
For the third type, the nonlinearity prevents the existence of a
transfer function.
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20. Introduction
Elements of Communication Systems
Classification of Communication Systems
Linear Distortion includes any amplitude or delay distortion
associated with a linear transmission system
Nonlinear Distortion A system having nonlinear elements
cannot be described by a transfer function. Instead, the
instantaneous values of input and output are related by a
curve or function y(t) = T[x(t)], commonly called the
transfer characteristic.
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21. Introduction
Elements of Communication Systems
Classification of Communication Systems
Equalization
Linear distortion-both amplitude and delay-is theoretically curable
through the use of equalization networks.
Figure 4: Channel with equalization for linear distortion
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22. Introduction
Elements of Communication Systems
Classification of Communication Systems
Companding
To utilizes two nonlinear signal processors, a compressor at
the input and an expander at the output as shown below
Figure 5: Companding System
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