EIE 312
Moodle 1
COMMUNICATION SYSTEMS
Outline
• Electrical Communication System
• Analog Communication System
• Digital Communication System
• Mathematical Models for Communication
Channels
Historical Background
• Telecommunications development has been
the result of timely use of newly discovered
technical features by ingenious pioneers
who had the vision to create new
applications.
Telegraphy
• It is any machine or system that allows the
transmission of information by coded signal
over distance. A message sent this way is
called a telegram, while someone who
operates the machine is known as a
telegrapher. Telegraphy was a major mode of
communication from mid 1800s until 1900s,
before eventually being replaced by
inventions like the telephone and the
Internet.
Telegraph Device
Historical Background(contd)
• Morse code was invented by Samuel Morse
in
1837(e.g.
letters(A-Z),numbers(1,2,3..)
Punctuation and Special Characters .,:?)
binary digital communication system
Historical Background(contd)
• Emile Baudot developed the Baudot code for
telegraphy in 1875 , each letter was encoded
into fixed-length binary code words of length
5
Historical Background(contd)
Telephone
• Telephone is an instrument that sends and
receives information usually by means of
electricity.
• The word telephone comes from Greek word
meaning “far and sound”.
• The telephone is one of the best ways to
communicate and can be made almost
everywhere in the world. Through the use of
a telephone life's can be saved in cases of
emergency.
Box Telephone
• Alexander Graham Bell while experimenting
with telegraph instruments in the early
1870s, he realized it might be possible to
transmit the human voice over a wire by
using electricity. His interest in electricity
continued and he attempted to send several
telegraph messages over a single wire at a
time.
• Lacking the time and skill to make the
equipment for these experiments he enlisted
the help of Thomas A. Watson from a nearby
electrical shop.
• The two became friends and worked together
on the experiment to produce sounds over
the "harmonic telegraph." It was on June 2,
1875, while Bell was at one end of the line
and Watson worked on the reeds of the
telegraph in another room that he heard the
sound of a plucked reed coming to him over
the wire.
subsequently, after much tinkering, the
instrument transmitted the sound of Bell's
voice to Watson. The instrument transmitted
recognizable voice sound, not words.
• Bell and Watson experimented all summer
and in September, 1875, Bell began to write
the specifications for his first telephone
patent. Bell's greatest success was achieved
on March 10, 1876, this marked not only the
birth of the telephone but the death of the
telegraph as well.
Different Types of Telephones
Historical Background(contd)
Wireless Communications
• James C. Maxwell in 1864 predicted the
existence of electromagnetic radiation and
formulated the basic theory (Maxwell's
equations)
• Maxwell's theory was verified experimentally
by Hertz in 1887
• On December 12, 1901, Guglielmo Marconi
successfully invented wireless telegraph to
send signal across Atlantic ocean
Historical Background(contd)
from cornwall to Newfoundland a distance of
about 1800 miles
• Amplitude modulation (AM) broadcast
started in 1920.
• Edwin Armstrong built and demonstrated the
first
frequency
modulation
(FM)
communication system in 1933.
Historical Background(contd)
• First television system was built in the
United States by Vladimir Zworykin and
demonstrated in 1929
• Satellite named Telstar 1 was launched in
1962 and used to relay TV signals between
Europe and the United States.
Historical Background(contd)
• Commercial
satellite
communication
services began in 1965 with the launching of
the Early Bird satellite
• First global mobile satellite communication
system (Iridium) came into operation in 1999.
• Mobile cellular systems was developed since
1980‘ e.g. analog (TACS, AMP),digital (GSM,
CDMA)and third generation (wideband
CDMA)
Overview of a communication
systems
• Communication system conveys information
from one point to another through a series of
certain processes.
• The system is designed to send information
from a source to one or more destinations
some distance away .
Basic Communication Block
Diagram
• The Figure below depicts the functional
elements of a communication system.
• There are five essential components of any
communication system, and each plays a
particular role in signal transmission, as
follows:
Functional block diagram of a
communication system
Elements of a Communication
System
Information source
• The information source acts as an interface
between the communication system and the
outside world and provides the message
signal that is processed by the transmitter.
There are three main classes ,namely voice
(speech/audio source), picture (image/video
source), text or data
Elements of a Communication
System(contd)
Input Transducer
• It converts the output of the information
source into an electrical signal that is
suitable for transmission. For instance, a
microphone serves as the transducer that
converts an acoustic speech(sound) signal
into an electrical signal, a video camera
converts an image into an electrical signal.
Elements of a Communication
System(contd)
Transmitter
• It converts the electrical signal into a form
that is suitable for transmission through the
physical channel or transmission medium.
e.g. Modulator or amplifier
For instance, the Federal Communications
Commission (FCC) specifies the frequency
range for each transmitting station(radio and
TV broadcast). Hence, the transmitter must
translate the information signal
Elements of a Communication
System(contd)
into the appropriate frequency range that
matches the frequency allocation assigned
to the transmitter so that signals transmitted
by multiple radio stations do not interfere
with one another.
Communication Channels and
their Characteristics
Transmission Channel
• This is the physical medium that bridges the
distance from transmitter to the receiver.
TELECOM MEDIA
MEDIA
GUIDED
UNGUIDED
Wired Communications Channels: These are
physical mediums that can be used to
transmit data from one point to another.
 Twisted pair cable (1–128 Mbps): Twistedpair cable consists of two strands of
insulated copper wire, twisted around each
other to reduce interference from electrical
fields. Example the telephone line is a
twisted-pair cable.
TWISTED PAIR CABLE
 coaxial cable (up to 200Mbps): consist of an
insulated thick copper wire wrapped in solid
or braided metal shield, then in an external
plastic cover. It is used for higher bandwidth
communications than twisted pair. Example
Television cable (i.e. Optus cable)
COAXIAL CABLE
 Fibre optic cable (100Mbps to 2Gbps): It
consists of hundreds of thin strands of
glass/plastic fiber that transmits data
through pulses of light rather than electronic
signals eliminating the problem of electrical
interference. These strands, each as thin as a
human hair, can transmit up to 2 billion
pulses per second (2Gbps). Example used
for internet back bones
Communication Channels and
their Characteristics(contd)
Wireless/Non Cable methods communication
channels: These are channels that can be
used to transmit data through free space.
Example satellite, microwave, infrared, and
Bluetooth.
Free Space: When free space is the medium,
the resulting system is known as “radio”.
Radio is the broad general term applied to
any form of wireless communication from
one point to another.
 Infrared transmission (1– 4 Mbps): Infrared
wireless transmission sends data signals
using infrared-light waves. Infrared ports can
be found on some laptop computers and
printers, as well as wireless mouse.
 Bluetooth: Bluetooth is a short range
wireless personal area network technology
used to exchange information between
wireless devices such as computers, cell
phones within 10m distance.
 Communications satellites: Communication
satellites are microwave relay stations in the
orbit around the earth. Transmitting a signal
from a ground station to a satellite is called
up-linking; the reverse is called downlinking.
• Broadcast radio (up to 2 Mbps): These is a
wireless transmission medium that sends
data over long distances between regions,
states, or countries.
• Microwave radio (45 Mbps): Microwave radio
transmits voice and data through the
atmosphere as super high frequency radio
waves.
Whatever the physical medium for signal
transmission, the essential feature is that
every channel introduces some amount of
transmission loss or attenuation, such that
the
transmitted
signal
undergoes
degradation from transmitter to receiver.
Attenuation is undesirable, thus reduces the
signal strength at the receiver.
Although this degradation may occur at any
point of the communication system, it is
usually associated with the channel alone
and often results from noise and other
undesired signals or interference.
Communication Channels and
their Characteristics(contd)
Receiver
• The function of the receiver is to recover the
message signal contained in the received
signal. Its operations include amplification to
compensate
for
transmission
loss,
demodulation and decoding to reverse the
signal-processing
performed
at
the
transmitter.
• Output Transducer: converts electric signal
to the desired message form. For instance
loudspeaker, images etc
Illustration
TRANSMISSION LIMITATIONS
• The
fundamental
limitations
of
communication systems can be classified
into two categories:
 Technological problems: These is made up
of constraints availability of hardware,
government regulations etc
 Physical limitations : These is subjected to
the law of nature in decision whether a given
assignment can be achieved or not.
TRANSMISSION
LIMITATIONS(CTND)
The fundamental limitations of information
transmission by means of electrical signals
are “Bandwidth and Noise”.
 Bandwidth: The amount of data which can be
transmitted on a medium over a fixed amount
of time (second). It is measured on Bits per
Second or Baud
• Bits per Second (bps): This is a measure of
transmission speed. The number of bits (0 or
1) which can be transmitted in a second.
• Baud Rate: This is a measure of how fast a
change of state occurs i.e. a change from 0
to 1
 Noise: These are unwanted waves that tend
to disturb the transmission and processing
of messages and could be internal or
external to the system.
Transmission Direction
• Simplex
• Half duplex
• Full Duplex
Simplex Transmission
simplex:
One
direction
only
Half Duplex Transmission
Half duplex: Both
directions but
only one
direction at a
time
Full Duplex Transmission
Full duplex:
send and
receive
both
directions
at once
Analog Communication
system
Analog Communication System
Analog systems convert analog message into
signals that can propagate through the
channel.
• Analog sources: are information sources that
produce analog signals
• Analog signals : are continuous-time signal
waveforms and can have an infinite number
of values in a range
• Analog
communication
systems:
are
systems that transmits analog signals
directly via carrier modulation over the
communication channel and demodulate
accordingly at the receiver e.g. AM, FM
Digital Communication
System
Digital Communication System
• Digital systems convert bits(digits, symbols)
into signals
• Digital signals are transmitted via digital
modulation and demodulated as a digital
signal at the receiver
Advantages of Digital
Communication Systems
• Digital signals are better suited to
processing and multiplexing than analog
signals.
• Digital transmission systems are more noise
resistant than the analog transmission
systems.
• Digital systems are better suited to evaluate
error performance.
• Provides better security by the use of data
encryption.
• Inexpensive digital circuits may be used.
Disadvantages of Digital
Communication Systems
• Analog signal must be converted to digital
codes prior to transmission and converted
back to analog form at the receiver, thus
necessitating additional encoding and
decoding circuitry.
• Digital communications require greater
bandwidth than analogue to transmit the
same information.
• The detection of digital signals requires the
communications system to be synchronized,
which is not with analogue systems.
Mathematical Models for
Communication Channels
• In the design of communication systems for
transmitting information through physical
channels, it
is appropriate to construct
mathematical models that reflect the most
important characteristics of the transmission
medium.
• The mathematical model for the channel is
used in the design of the channel encoder
and modulator at the transmitter and the
demodulator and channel decoder at the
receiver.
The Additive Noise Channel.
The Additive Noise Channel.
• The simplest mathematical model for a
communication channel is the additive noise
channel as illustrated below
where
s(t)= transmitted signal
n(t)= additive random noise process
r(t)= received signal
In this model the transmitted signal s(t) is
corrupted by an additive random noise
process n(t).
• In wireless channels noise can be generated
due to interference encountered during
transmission. But if noise arise from
electronic components then its thermal
noise.
• if the signal undergoes attenuation in
transmission through the channel, the
received signal is
r(t) =α ⋅ s(t) + n(t) where α is the attenuation
factor.
Linear filter channel with
additive noise.
The linear filter channel
• In some physical channels such as wire-line
telephone channels, filters are used to
ensure that the transmitted signals do not
exceed specified bandwidth limitations, such
that signals do not interfere with one
another. These channels are characterized
mathematically as linear filter channels with
additive noise as illustrated below. if the
channel input is the signal s(t), the channel
output is the signal
r(t) = s(t) ∗ c(t) + n(t)
Linear time-variant filter
channel with additive noise.
• Physical channels such as underwater
acoustic channels and radio channels at
frequencies below 30 MHz result in timevariant multipath propagation of the
transmitted
signal
are
characterized
mathematically as time-variant linear filters.
Therefore for an input signal s(t), the channel
output signal is
where
c(τ ; t) : time-variant channel impulse response
of the channel at time t due to an impulse
applied at time (t - τ )
The End