Telecommunications

Velar H. Elias

velar82@hotmail.com
Content
-----------------------------------------------
• Learning outcomes.
• Introduction to communication system.
• Type of communication system.
• Transmission types.
• Communication channel.
• Analog & digital modulation.
• Basic analog communication system.
• Need of modulation.
• Modulation types.
• Home work.
• References.
Learning outcomes
At the end of the lecture, the learner will be able
to:
• Explain the principles of a communication
systems
• Discuss the nature of medium channel.
• Make the distinction between analog and digital
signal.
• Determine the need of modulation and
differentiate various type of modulation
techniques
Definitions

• Communications:
Transfer of information from one place to
another.
Should be efficient, reliable, and secured.

• Communication system:
components/subsystems act together to
accomplish information transfer/exchange
Definitions (Cont’d)
• Electronic communication system
transmission, reception and
processing of information between
two or more locations using
electronic circuits.
• Information source
analog/digital form
Information, message and signals

• Information
The commodity produced by the source for
transfer to some user at the destination.
• Message
The physical manifestation of information
as produced by the information source.
• Signals
A physical embodiment of information –
voltage signal or current signal
Need For Communication

• Importance of communication:
exchange of information between two
parties separated in distances in a
more faster and reliable way.
Introduction to communication system
• Communication is participated process intent to
transfer information from one place to another.
• A significant point about communication is that
it involves a sender (transmitter) and receiver.

Channel
receiver sender

Feed back
 Information transfer system block diagram
Information sources
> Audio
Processing
> Video Transmitter
> Data (modulator)
(with their respective
transducers)
Transmission
medium
Reproduced information
Audio
Receiver /
Video Transducers Processing
Data (demodulator)
Type of communication system
• Electronic communications are classified
according to whether they are
1. Type of transmission:
a. One-way (simplex) transmissions.
b. two-way (full duplex or half duplex)
transmissions.
2. Type of channel medium:
a. Wire-less communication.
b. Wire-line communication.
3. Type of modulating signal:
a. Analog modulation.
b. Digital modulation.
Transmission types-I
Simplex
The simplest method of
electronic communication is
referred to as simplex.

This type of communication

is one-way. Examples are:
▫ Radio
▫ TV broadcasting
Transmission types-II
Full Duplex
▫ Most electronic
communication is two-way
and is referred to as
duplex.

▫ When people can talk and

listen simultaneously, it is
called full duplex.
 Telephone, Cell phone
 Internet
Transmission types-III
Half Duplex
▫ The form of two-way communication in which
only one party transmits at a time is known as
half duplex. Examples are:
 Police, military, etc. radio transmissions
 Walky-talky
communication channel
• The communication channel is the medium
by which the electronic signal is sent from one
place to another through it.
▫ Types of media include
 Free space
 Electrical conductors
 Optical media
 waveguide
Analog & Digital modulation-I
• Analog referred to the system that used analog
signals (continuous with time) for all processes that
preferred in transmitter and receiver.
 Sine wave
 Voice
 Video (TV)
• Digital referred to the system that used digital
signals (discrete with time) for all processes that
preferred in transmitter and receiver.
▫ Most digital signals use binary or two-state codes.
Examples are:
 Telegraph (Morse code)
 Continuous wave (CW) code
 Serial binary code (used in computers)
Analog & Digital modulation-II
• Modulation is the process of changing some
property of the information sources into suitable
form for transmission through the physical
medium/channel.
▫ It is performed in the Transmitter by a device
called Modulator.
• Demodulation is the reverse process of
modulation by converting the modulated
information sources back to its original
information (it removes the carrier from the
information signal).
▫ It is performed in the Receiver by a device called
Demodulator.
 18

Basic analog communication system

EM waves (modulated
signal)
Baseband signal
(electrical signal) Transmitter

Input Transmission
Transmission
transducer Modulator channel
Channel

Carrier
Baseband signal
(electrical signal) Receiver
EM waves (modulated
Output signal)
Demodulator
transducer
Analog vs. Digital
• Analog
Continuous Variation
Assume the total range of
frequencies/time
All information is transmitted
• Digital
Takes samples:
 non continuous stream of on/off pulses
Translates to 1’s and 0’s
 Analog vs. Digital

• Digital CS
Advantages: • Analog CS
-Privacy preserved(data Disadvantages:
encrypted)
-Can merge different data -No privacy preserved
-error correction -Cannot merge different data
- high immunity to noise -No error correction capability
- Susceptible to noise
Disadvantages: Advantages:
-synchronization problem is -synchronization problem is
relatively difficult relatively easier.
Basic Requirements of Communication
System
• Rate of information transfer:
how fast the information can be
transferred
• Purity of signal received:
whether the signal received is the same
as the signal being transmit
• Simplicity of the system
the simpler the system, the better
• Reliability
Trade-off between analog and digital
modulations
Analog modulation
Wide bandwidth
medium
Simple Simple
modulation demodulation
and hardware and hardware

Digital modulation
Narrow bandwidth
Complex medium Complex
modulation demodulation
and hardware and hardware
A Communication System as a System
Example
• A communication system has an information
signal plus noise signals
• This is an example of a system that consists of
an interconnection of smaller systems
Signal Types
Conversions Between Signal Types

Sampling

Quantizing

Encoding
Sound Recording System
Recorded Sound as a Signal Example

• “s” “i” “gn” “al”

W2-1

Elements of Communication
System(CS)
Elements of CS(cont’d)
• Information
The communication system exists to convey a
message.
Message comes from information source
Information forms - audio, video, text or data
cont’d…
• Transmitter:
Processes input signal to produce a transmitted
signal that suited the characteristic of transmission
channel.
E.g. modulation, coding, mixing, translate
Other functions performed - Amplification,
filtering, antenna
Message converted to into electrical signals by
transducers
E.g. speech waves are converted to voltage
variation by a microphone
Elements of CS(cont’d)

• Channel (transmission media):

a medium that bridges the distance from source to
destination. Eg: Atmosphere (free space), wires,
coaxial cable, fiber optics, waveguide
signals undergoes degradation from noise ,
interference and distortion
Elements of CS(cont’d)
• Receiver:
to recover the message signal contained in the
received signal from the output of the channel,
and convert it to a form suitable for the output
transducer.
E.g. mixing, demodulation, decoding
Other functions performed: Amplification,
filtering.
Transducer converts the electrical signal at its
input into a form desired by the system used
Various forms of communication
system

• Broadcast: radio and television

• Mobile communications
• Fixed communication system- land line
• Data communication-internet
Need of modulation
1. Ease of radiation
Wavelength (λ) = speed of light (c) ÷ frequency (f)
Length of antenna (L) =wavelength ÷ 10
2. Reduce noise & interference
3. Overcome equipment limitation
4. Frequency assignment
5. For multiplexing
Need of modulation
• •To reduce noise and interference
• •Interference can be eliminated, although in
theoretically noise cannot eliminated.
• •So certain modulation methods are used to
reduce noise but usually by increasing
bandwidth
• •Bandwidth needed >> Original bandwidth
Need of modulation
• •Frequency assignment
• •Proper assignment of frequencies for different
types of communication, reduce inter-symbol-
interference ISI and increase data rate.
Need of modulation
• For Multiplexing
• •Sending many signals in one channel (wire,
cable …..

• •Ex: telephone
Need of modulation
• •To overcome equipment limitation
• •To place signals in the proper frequencies
where equipment are available.
Modulation types
Modulation

Analog

AM FM PM

pulse

digital

PAM PWM PPM

ASK FSK PSK QAM

Home work
• Determine the wavelength and antenna size for
the following devices:
▫ Home electricity.
▫ FM radio device.
▫ Satellite device.
▫ Mobile device.
▫ Microwave oven.

Use internet, catalogs or device features to

determine the operate frequency.
references
• U. A. Bakshi & A. P. Godse, “Analog
communication”, second edition-2009.
• M. L. Anand, “Electronic Communications”, first
edition-2004.
• Leon W. Couch, “Analog and Digital
Communication system”, fifth edition-2007.
• Abhishek Yadar, “Analog Communication
system”, second edition-2009.
references
• Wayne Tomasi, “ Electronic Communication Systems
Fundamentals Through Advanced” 5th Ed, Prentice
Hall, 2004.

• Paul Young, “Electronics Communications

Techniques”, 5th Edition, Prentice Hall, 2004.

• Mullet , “Basic Telecommunications:The Physical

Layer”, Thomson Learning, 2003.