This document provides an introduction to communication systems. It defines communication as the exchange of information from a source to a destination. An electronic communication system is defined as the whole mechanism of sending, receiving, and processing information electronically from source to destination. The main objectives of a communication system are to produce an accurate replica of the transmitted information and to transfer information between two or more points with minimum error. The basic elements of a communication system are an information source, transmitter, channel, receiver, and destination. Modulation is the process of modifying a carrier wave systematically by a modulating signal to make it suitable for transmission through a channel. There are two main types of modulation: analog modulation and digital modulation.

1. 1
Introduction to Communication Systems
Communication – Basic process of exchanging
information from one location (source) to
destination (receiving end).
Refers – process of sending, receiving and
processing of information/signal/input from
one point to another point.
Source Destination
Flow of information
Figure 1 : A simple communication system

2. 2
Electronic Communication System – defined
as the whole mechanism of sending and
receiving as well as processing of information
electronically from source to destination.
Example – Radiotelephony, broadcasting,
point-to-point, mobile communications,
computer communications, radar and satellite
systems.

3. 3
Objectives
Communication System – to produce an
accurate replica of the transmitted
information that is to transfer information
between two or more points (destinations)
through a communication channel, with
minimum error.

4. 4
NEED FOR COMMUNICATION
Interaction purposes – enables people to interact in
a timely fashion on a global level in social, political,
economic and scientific areas, through telephones,
electronic-mail and video conference.
Transfer Information – Tx in the form of audio, video,
texts, computer data and picture through facsimile,
telegraph or telex and internet.
Broadcasting – Broadcast information to masses,
through radio, television or teletext.

5. 5
Terms Related To Communications
 Message – physical manifestation produced by the
information source and then converted to electrical signal
before transmission by the transducer in the transmitter.
 Transducer – Device that converts one form of energy into
another form.
 Input Transducer – placed at the transmitter which convert an
input message into an electrical signal.
 Example – Microphone which converts sound energy to
electrical energy.
Message
Input
Transducer
Electrical
Signal

6. 6
 Output Transducer – placed at the receiver which
converts the electrical signal into the original
message.
 Example – Loudspeaker which converts electrical
energy into sound energy.
 Signal – electrical voltage or current which varies
with time and is used to carry message or
information from one point to another.
Electrical
Signal
Output
Transducer
Message

7. 7
Elements of a Communication System
The basic elements are : Source, Transmitter,
Channel, Receiver and Destination.
Information
Source
Transmitter
Channel
Transmission
Medium
Receiver Destination
Noise
Figure : Basic Block Diagram of a Communication System

8. 8
Function of each Element.
Information Source – the communication system
exists to send messages. Messages come from voice,
data, video and other types of information.
Transmitter – Transmit the input message into
electrical signals such as voltage or current into
electromagnetic waves such as radio waves,
microwaves that is suitable for transmission and
compatible with the channel. Besides, the
transmitter also do the modulation and encoding (for
digital signal).

9. 9
Block Diagram of a Transmitter
Modulating
Signal
Audio
Amplifier
Modulator
RF
Amplifier
Carrier
Signal
Transmitting
Antenna

10. 10
Channel/Medium – is the link or path over
which information flows from the source to
destination. Many links combined will
establish a communication networks.
There are 5 criteria of a transmission system;
Capacity, Performance, Distance, Security and
Cost which includes the installation, operation
and maintenance.
2 main categories of channel that commonly
used are; line (guided media) and free space
(unguided media)

11. 11
Receiver – Receives the electrical signals or
electromagnetic waves that are sent by the
transmitter through the channel. It is also separate
the information from the received signal and sent
the information to the destination.
Basically, a receiver consists of several stages of
amplification, frequency conversion and filtering.

12. 12
Block Diagram of a Receiver
Destination – is where the user receives the
information, such as loud speaker, visual display,
computer monitor, plotter and printer.
RF
Amplifier
Mixer
Local
Oscillator
Intermediate
Frequency
Amplifier
Demodulator
Audio
Amplifier
Destination
Receiving Antenna

13. 13
Analog Modulation
• Baseband Transmission
– Baseband signal is the information either in a
digital or analogue form.
– Transmission of original information whether
analogue or digital, directly into transmission
medium is called baseband transmission.
– Example: intercom (figure below)
MicrophoneVoice
Audio
Amplifier
Audio
Amplifier
Speaker
Voice
Wire

14. 14
Baseband signal is not suitable for long
distance communication….
• Hardware limitations
– Requires very long antenna
– Baseband signal is an audio signal of low frequency. For
example voice, range of frequency is 0.3 kHz to 3.4 kHz.
The length of the antenna required to transmit any signal
at least 1/10 of its wavelength (λ). Therefore, L = 100km
(impossible!)
• Interference with other waves
– Simultaneous transmission of audio signals will cause
interference with each other. This is due to audio signals
having the same frequency range and receiver stations
cannot distinguish the signals.

15. 15
Modulation Modulation – defined as the process of modifying a carrier
wave (radio wave) systematically by the modulating signal.
 This process makes the signal suitable for transmission and
compatible with the channel.
 Resultant signal – modulated signal
 2 types of modulation; Analog Modulation and Digital
Modulation.
 Analogue Modulation – to transfer an analogue low pass
signal over an analogue bandpass channel.
 Digital Modulation – to transfer a digital bit stream the carrier
is a periodic train and one of the pulse parameter (amplitude,
width or position) changes according to the audio signal.