Transcript Introduction to telecommunication_part 1

EKT 231
COMMUNICATION
SYSTEM
MEETING
 LECTURE
 LABORATORY
: 3 HOURS
: 2 HOURS
LECTURER
PUAN NORSUHAIDA AHMAD
04-9798416
[email protected]
Other Lecturers

Pn Sabarina /Pn Yusnita
 Microelectronics

PM Dr Brijmohan/Pm Dr R. Badlishah
 Industrial

Electronic & Electrical System
Cik Junita
 Electronics
& Mechatronics
OBJECTIVES
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To understand and use various terminologies in Communication
System.
To emphasize on the importance of modulation and demodulation of
analog signals along with associated system design issues.
To be able to select a channel and assimilate associated peripherals
for DAQ and signal processing.
To characterize amplitude, double-sideband and single sideband
modulated waveforms in the time and the frequency domains.
To characterize frequency and phase modulated signals in the time
domain and tone modulated signals in the frequency domain.
To study the quantization process in a pulse code modulation system
in terms of how it is created and how to minimize its effect.
To assimilate SNR in various system.
Textbook

Mullet “Basic Telecommunications : The
physical layer", Thomson Learning, 2003.
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Ziemer/Tranter “Principles of
communication systems, modulation and
noise, 5th Ed, Wiley,2002
References
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Wayne Tomasi, “ Electronic Communication
Systems Fundamentals Through Advanced” 5th Ed,
Prentice Hall, 2004.
William Schweber, “ Electronic Communication
Systems- A complete Course”, Prentice Hall, 1999.
Haykin Simon, “Communication System” 4th Ed.
Lathi B.P “Modern Digital & Analog
Communication System”
Blake “Electronic Communication System”
Assessment

Final Exam = 50 %

Coursework = 50 %
 Assignments/Quiz
=5%
 Tests = 15 % (test 1, test 2 & test 3)
 Labs/Tutorials = 30 %
Communication System
Communication system is
IT DEALS in
alternatively known as
TELECOMMUNICATION
It deals in
Tele-Communication of
Audio
Video
and/or
Data
COMMUNICATION
means
and/or
and/or
For conveying
information and thoughts,
we need
in depth vocabulary.
In depth Vocabulary means:
Specific words for specific sense.
Primitive communication …..
In primitive times, when vocabulary was
in infancy, communication was through
 facial
expressions,
 vocal sound and
 body language were used to express,
as we do to a dumb-person or, pet
animal.
Improved primitive communication
was basically digital…..
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
Earlier telecommunication incorporated the
coded position of torches; had to be in LOS;
were error prone.
Improved by use of drum beatings;
LOS not needed,
information could be repeated in speed.
Coding information possible.

Multi colored flags in different position
represented different meanings. Improved
coding. Has to be LOS.
As vocabulary and technology of
printing improved….
began sending of
Written or verbal message through man
and
 Written/pictorial message by trend birds.

Today..
Perspective is altogether changed.
 We have ever improving vocabulary, voice
and video communication and soft and hard
printing technology.
 Most work, including purchases and bank
transactions are executed from home, on
net.

Cont’d…



Hard printing restricted, soft printing
encouraged and e_communication promoted.
Net is an intelligent, smart and active
communication link between electronic gazettes
including computers.
Internet besides computer, is now accessible
on: personal diaries, mobile phone, VoIP
phones, TVs etc.
Present era is information age
Information is available in abundance.
 This leads to knowledge that helps to develop
strategy.
 It has become possible due to availability of
Communication channels, that include data
acquisition, transmission and reception.
 High degree of intelligence and security has
been included into these channels to take
appropriate decisions.

Intonation
is the process of
communicating quality of
feelings/emotions.
The process includes
pitch in the vocal card enhanced by music,
body language with expressions on face
and eye.
Diagrams, graphs, pictures and photos.
intonation is unmasked expression
Providing
 media
for tele-communication
including multi-media and data
communication
and

Providing controlled QoS.
History
Evolving of Communication System took
centuries of hardships.
 Techniques developed were mathematically
founded and accelerated by material cum
fabrication science.
 Looking to the rate of development, it still
seems to be in infancy stage.
 Now we see the history of advancement.

Terminology in
Communication
Purpose is to
familiarize & correlate
the terminologies for
Communication Systems.

Power: a measure of time rate of energy
spent or, generated.
Units  watts  scalar.
For the instant values of variables voltage v(t)
volt and current i(t) ampere in a circuit or it’s
any element, the average power in watts
consumed is time integral of the product of
instant values of voltage and currents over a
period of time (t2-t1).
 P ={ v(t)i(t) dt}/(t2-t1) Watt
Divided by over a time “(t2-t1)”
Non-zero power
P
will be non zero for (t2-t1)=T,
if and only if
the two variables v(t) and i(t)
(a) have same periodicity, T
and/or
(b) not in quadrature phase.
Calculation of Power by Graph
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
Tabulate the Multiplication of v(t) and i(t)
at different instances of time in seconds.
Plot them with time as x-axis.
The area under the curve between the
time limit corresponds to the integral.
It is equal to the work done, in wattsecond.
Cont’d…


The average power is obtained by divide
the area obtained by the time limit.
In place of voltage and current, the
variables can be torque and angular
velocity; force and velocity etc.
If the frequency of the two signals is not
same, power developed by them over
composite period is essentially zero.
Alternatively:
If the periodicity of the two signals differ, the
integral over the composite period will always
be zero.
This we have seen while computing the coefficients
of a wave by Fourier Series.
Example: Calculation of Average power
v(t)= Vp cos(t+) and i(t) = Ip(t+)
1 
P( t ) 

T 
T
v ( t ) i( t ) d t
0

T
1 

T 
V cos  t    I  cos  t    d t
p
p
0
V I

p
T
p 


T
cos  t    cos  t    d t
0
 Vp  Ip  T


 cos       cos  2t   d t


 2 T 

0


If Vp/2
P( t )
=V and Ip/ 2 =I :: effective values
 V I cos     
For average Power: V and I should be effective values
Average Power by dot product
 Let V(t) = |V| = iVcos + jVsin
 and I(t) = |I|  = I Icos + j I sin;
 P(t) =V(t).I(t) =Vcos()xIcos() + Vsin()xIsin()
= VI cos(-)
Angle between
the two
vectors
same
Average Power by complex variable
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Let V(t) = |V| =Vcos + jVsin
and I(t) = |I|  =Icos + j I sin ;
Complex conjugate of I(t) = I*(t) = |I| - = Icos - j I sin 
V(t)I*(t) = VI[cos()cos() + sin()sin()]
= VI cos(-)
Power gain
Signal level gain
signal gain
In Engineering Problems, we have known
the term signal gain / mechanical
advantage;
Examples are chain pulley block, cantilever,
gear, amplifier, transformer.
 Voltage amplifier: Av= Vo/Vi.

Cont’d…
Transistors current gain:  = ic/ib,
 Chain pulley block: weight lifted/weight
applied.
 Transformer: secondary voltage/primary
voltage
 gear box: output torque/input torque.

Power gain
It is the ratio of output power over input power.
Ap = Po/Pi.
 If the energy is consumed in doing a work,
Power gain is always  1.
 Example is transformer, chain pulley block, gear
boxes etc have power gain less than one.
 In amplifiers, the apparent power gain may be
more than one. The signal power is amplified.
DC electric power is transformed into signal
power.

In signal gain:
The advantage or, signal gain may be >1
though the power gain is < 1.
 At first instance, it appears that there is no
apparent relation between signal gain and
power gain.
 It is because the friction of the load in which the
power is fed, is not accounted.

Power and voltage gain in
communication
In communication, due to known
characteristic impedance of the
channel, the power and voltage gains
become explicit.
 It is designated in terms of decibels, dB.
 Power gain in dB = 10 log (Po/Pi) dB.
Voltage gain in dB = 20 log (Vo/Vi) dB.
Here if power gain < 1, voltage gain <1.

Here the load impedance in which the power of the
signal fed, is predefined.
Zo is generally the load or, source impedance in
communication channels.
Zo for a given channel is generally fixed.
The source as well as load impedance are matched with
the characteristic impedance, Zo.
It is because our interest in tele-communication
transmission lies in maximum power transfer.
The maximum efficiency thus is 50%.
This implies that voltage gain and power gain go hand
to hand in communication system.
Standard characteristic
impedances of various channels
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Audio Applications:
Twisted pairs:
600 ohm
100 ohm
one twist per 4 cm.
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Cables TV
RF signal delivery
Air
75 ohm
50 ohm
377 ohm
We are yet to discuss channel’s characteristic
impedance as frequency dependant.
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Power gain in dB =10 log (Po/Pi) dB.
Voltage gain in dB = 20 log (Vo/Vi) dB.
are absolute gains
power ratio Po/Pi = 10,000 = 40 dB
Voltage ratio Vo/Vi = 100 = 40 dB.
See that
Po/Pi = (Vo/Vi)2
Term is power
(Po/Pi) dB = 2(Vo/Vi)dB
For the power gain
2n = 3n dB.
Voltage gain is
2n = 2x3n dB
For that power gain 10n = 10n dB
Voltage gain of
10n = 2x10n dB
In attenuation, gain < 1, the dB gain is negative.
Alternatively:
(gain in dB/10)
Power gain
= 10
Voltage gain
= 10 (gain in dB/20)
Examples:
A 64 dB gain means 106.4 = 2.5212x106 watts.
An attenuation by
0.01= 10 log(0.01)
= -20 dB
Examples:
Let there be two amplifiers in cascade.
Their gains are 13 dB and 10 dB Sum
respectively.
 The overall gain is 13+10 = 23 dB.
 In terms of ratio:
 23 dB = 10(23/10)= 200
 13 dB = 10(13/10)= 20
same
 10 dB = 10(10/10)= 10
 Again 20 x 10 = 200.

multiplication
Relative dB
It is convenient to express signals with some
reference such as
1mW power or,
1 V voltage level.
 This permits input- and output- signals to be
expressed in terms of relative dB.
 When referenced to 1mW, it is written dBm
 When referenced to 1 V, it is written as dBV

Relative dB is not a gain
but is termed as gain wrt a reference.
5 watts signal,
 In relative dB; 10 log(5W/1mW) = 36.99 dBm
 500 V signal:
 In relative dB; 20 log(500/1)
= 53.98 dBV

Application

Reference gain
Input to an amplifier is -12 dBV . The gain of
the amplifier is 27 dB. The overall gain is 12+27 = 15 dBV.
Absolute gain
Note here that input signal is relative to 1 V.
 The gain of the amplifier is absolute.
 Output signal is again relative to 1 V.

Why dB representation?
 The
concept of decibels originated from
the term of sound “loudness”.
 Double (half) the power does not mean
double (half) the loudness. It follows the
log rule: 10 log(Po/Pi).
 It permits the large changes to be
incorporated in small displays that helps in
interpretation.
Advantages….
We can estimate the whispers as well as
loudness.
 It enables predicting the characteristics
without experimentation: Bode plot.
 Addition in dB is simple compared to
multiplication to get output for a given input
through a system.
 Specification are provided in dB.

Communication Process
The three basic factors that
quantify the communication
process:
Bandwidth
Power
Noise
Channel:
is a media through which communication proceeds.
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Basically it is a passive.
Inclusion of dynamic programming has made it
sufficient intelligence to take decisions and act.
They can
route.
.
They can detect and correct the error in the signal.
They can re-pack the signal-data.
Communication networks, channels, of today are
more flexible,
cost effective and
have better quality of service.
.
The three factors that control the
selection of a channel are:
.
Bandwidth of the channel
Its attenuation characteristics
Impairment of the signal due to
noise and
distortion
Channel capacity is decided by its susceptibility to noise.
Channel Capacity
Hartley Shannon proved that Maximum data rate
in a channel is governed by its
1.
Bandwidth
and
2.
SNR: signal to noise ratio.
An intelligible speech (audible) should have SNR > 10 dB.
Ex. A receiver input is 42.2 mW while the
noise is 33.3 W.
Soln. The SNR = 10 log (42.2 mW/33.3 W)
= 31.03 dB.
Every body says Noise is
detrimental…..
 What
is noise?
From where they come?
 Noise can be an unwanted part of the signal.
• It may be added to the signal by the

processing equipments,
 environment conditions of the channel
 and similar.

Part of the signal
When it is a part of the signal, a suitable
filter can remove the undesired part of the
signal.
 It equally reduces the noise also.
 The noise outside the desired frequency
range of signal can only be removed.

When it is external to signal:
It can be
due to processing equipments
or,
man made
or,
created by environment / atmospheric
or
due to solar-space characteristics.
Due to processing equipments
White Noise: it theoretically contains all
possible frequencies of same amplitude.
A time impulse has this characteristic.
The shot noise:
cause: abrupt variation in current flow/power flow:
can be considered as time-impulse.
Thermal noise also called Johnson noise also fall
under this category.
Thermal noise:
The thermal noise generated due to random
motion of electrons that produces “additional”
heat.
For the device of unknown resistance, its
equivalent resistance is calculated from the
heat developed.
The voltage level of the noise is then
calculated.
This noise is temperature dependent.
Can be controlled by controlling temperature.
Thermal noise
The Controlling equation for thermal noise
power and voltage are:
Pth= kTB
watt and
eth = [4kTBR] volt
where
 k = Boltzman constant =1.38x10-23 J/°K,
 T = temperature in Kelvin,
 B = Bandwidth
 R = equivalent resistance.
Note that
The equations
Pth = kTB
watt and
eth = [4kTBR] volt
indicate that available noise power from a
source does not depend on the value of
equivalent resistance but the open circuit rms
voltage does.

Couch-II Digital and analog communication system, 6/e, pp 579
Noise in active devices
Thermal noise developed by transistors,
ICs, diodes etc. is difficult to calculate.
Therefore they are experimentally found
out by the amount of heat developed.
The equivalent resistance is calculated.
Power flow generates noise

Flicker Noise:
This noise is inversely proportional to
frequency.
Has reduced effect at high frequency.
Prominent at low frequencies and it affects
the base-band signals.
Man made noises:

automobiles,
 computers,
 switching
electronics,
 power switches,
 commutator
 Sparking,
 Switching on and off of electric gazzets and
alike.

The range is upto 600 MHz.
[Kennedy et al,”Electronic communication Systems” 4/e pp14-32]
atmospheric
Thunder storm/Static discharge,
 Vicinity of radiating sources, such as
corona discharge, spark.
 Solar radiations.
 Many unknown sources those radiate
energy.
 Such noises are impulsive and occupy
radio frequency spectrum upto 30 MHz.

[Kennedy et al,”Electronic communication Systems” 4/e pp14-32]
NOISE FACTOR

The noise that has been multiplied during
transmission of the signal is:
NF = SNRinputdB – SNRoutputdB.
Ex: If the input SNR is 25 dB and NF = 10,
the output SNR in dB is 25 dB + 10 dB
=35 dB
System generated Distortion
An amplifier beside thermal noise, can
generate inter modulation signals and
harmonics.
 The later is due to operating point in non
linear region of transfer characteristic.
 A transfer characteristic with y as output
and x as input is defined by a power
series:
y = ao+a1x+a2x2+…..+aixi+……anxn+…

The power series :
y =ao+a1x+a2x2+…..+aixi+……anxn+…
 These coefficients are assumed to be constants.
 Except coefficients of x, other represent non-linearity.
y = ao+a1x
is linear in mathematical sense,
but it is nonlinear in engineering sense.
y = a1 x
is an LTI system equation in engineering sense.
 The values of other coefficients provide the measure
of non linearity.
 The non-linearity generates harmonics and intermodulation signals in the output.
Generates Harmonic Signals
Take the part of the equation:
y’ = a2x2.
 Let x = cos. x2 = cos2 = (1-cos 2)/2
 y’ = (a2/2) (1-cos 2)

2nd Harmonic generated
Coeff. 2
3rd Harmonic Generated
Try for
y”=a3x3.
 The result should be: y”= (a3/2) (cos - cos3)
 Output depends on the values of coefficients. If
say a3 =0; then y”….??

Inter-modulation distortion

Let x = (mcos  + ncos)
(hint take m = dcos and n = dsin)
Try both cases. y’ = a2x2
y”= a3x3
The output is inter-modulation distortion.
Phase distortion
Besides amplitude distortion due to non
linear transfer characteristic of the system,
there also exists a phase distortion.
 Phase distortion is due to non linear phase
delay vrs frequency characteristic of the
system.
 It does not affect the signal power but
does affect the properties of the signal.
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What does distortions do?
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Phase distortion results into hazy signal
reconstruction. In video, one will miss the
sharpness in the figures.
Phase distortion does not affect audio. It is due to
characteristics of our ear.
In Audio, due to amplitude distortion, generation of
harmonics distorts intelligence.
In video, amplitude distortion does not make too
much sense. It is due to characteristic of our eyes.
Signal and Noise
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Signal is a vector quantity.
Noise is a random signal from unknown sources.
Unwanted noise of signal is also termed as
noise.
When vectorially added, can randomly add or
subtract to the amplitude of the intelligence. The
resultant signal may not remain dependable. It
can create bit error in digital signaling.