SKEE 3533

COMMUNICATION PRINCIPLES
Yusri Md. Yunos, PhD, yusri@utm.my
P19- Level 5 (Workspace Room)
Course Outline:

1.50% Coursework
a. 20% Tests 1 & 2, Thursday evening, 3-7 pm, P16
 Test 1, 12 October 2017 – Intro, Noise & AM
 Test 2, 30 November 2017 – FM & Pulse Modulation
b. 10% Matlab Assignment
c. 15% Case study assignment
d. 5% Attendance & Quizzes
(instructions) (rubric matlab) (rubric paper)

2. 50% Final exam

a. <80% attendance – barred from attending exam

Notes:
1.Details on the topics for tests and assignments are in the e-learning
website. Assignment rubrics and Turnitin report must be submitted too.
2. Books: Pn Syukie Makmal Perhubungan Asas (35303)
 1.0 Introduction

“How do you want to send data/information to

someone who is far from you?”

“If the information that you want to send is your

voice, how to make sure that what you are
saying is understood by your friend?”

“What is the source and technology available

surround you that can help?”

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1.1 Communication System History
• 1837 – Samuel Morse invented telegraph.
• 1858 – First telegraph cable across Atlantic (Canada – Ireland)
• 1876 – Alexander Graham Bell invented telephone.
• 1888 – Heinrich Hertz demonstrated the existence of EM waves.
• 1897 – Marconi invented wireless telegraph.
• 1906 – Radio communication system was invented.
• 1923 – Television was invented.
• 1938 – Radar and microwave system was invented for World War II.
• 1950 – TDM was invented.
• 1956 – First telephone cable was installed across Atlantic.
• 1960 – Laser was invented
• 1962 – Satellite communication More current
• 1969 – Internet DARPA Development
• 1970 – Corning Glass invented optical fiber.
• 1975 – Digital telephone was introduced.
• 1985 – Facsimile machine.
• 1988 – Installation of fiber optic cable across Pacific and Atlantic.
• 1990 – World Wide Web and Digital Communication.
• 1998 – Digital Television.
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o International Telecommunication Union (ITU)

is the UN specialized agency for ICTs

o ITU-T produces international standards

known as ITU-T Recommendations

o Started in 1865

o Standards are critical to the global interoperability of ICTs

o Standards enable global communications by ensuring that

countries’ ICT networks and devices are speaking the same

language (whether we exchange voice, video or data messages)

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Why regulate telecommunication
ITU : enabling communication since 1865

1865 2017
ITU’s mission: committed to connecting the world

ITU-T
develops ICT and
telecommunication standards

ITU-R ITU-D
manages radio assists developing
spectrum and countries
satellite orbits

Three sectors of ITU

General Secretariat coordinates work of ITU

MCMC – MALAYSIA
POSITIVE IMPACTS OF COMMUNICATION SYSTEM
 NEGATIVE IMPACTS
EXAMPLE:
 1.2 Communication System
• Communication system – Process of sending information
signal from one point to another point - involves 3 important
processes ie:
Transmission
Receiving
Processing
• Eg: Telegraphy, telephony, facsimile, radio, satellite, optical
fiber system, cellular mobile.

mtx(t) mrx(t)
s(t) Input Comm Output r(t)
Transducer System Transducer

Fig. 1.1 Basic communication system

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 1.3 Basic Communication System
wired / wireless
mtx(t) ptx(t) prx(t) mrx(t)
Input Transmitter
Transmission Output
Receiver
Transducer Medium Transducer

s(t) r(t)

Noise n(t)

s(t) – Input signal; audio, video, image, data etc.

mtx(t) – Modulating signal; input signal that has been converted to electrical
signal.
ptx(t) – Modulated signal transmitted by the transmitter.
n(t) – Noise signal.
prx(t) – Modulated signal received by the receiver.
mrx(t) – Modulating signal at the receiver.
r(t) – Output signal.
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Pengenalan Kepada Sistem Perhubungan
 1.3.1 Component Function in Basic
Communication System
• Input Transducer – convert input signal, s(t) in electrical forms. eg:
microphone.

• Transmitter – involve modulation process – convert modulating signal,

mtx(t) to modulated signal, ptx(t). And finally transmit the signal.

• Transmission medium – connecting the transmitter and the receiver

that enable the modulated signal, ptx(t) propagate through the medium.

• Receiver – receive the modulated signal, prx(t) and then convert the
signal to modulating signal, mrx(t) through the process called
demodulation.

• Output Transducer – convert the modulating signal, mrx(t) to its

original forms (output signal), r(t) that is useful to the users. eg: loud
speaker.

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Pengenalan Kepada Sistem Perhubungan
 Analog vs Digital Systems
ANALOG DIGITAL

• Signal processed is analog, • Information signal can be digital

takes any value within a range or analogue signal (through A/D
conversion), takes limited no. of
values
• An audio amplifier produces an
output voltage which can be
any value within the range of its • A computer is a digital system
power supply. contains logic gates that takes
two values; true or false
• More sensitive to noise as noise • Noise is easier to distinguish as
is harder to be distinguished the desired signals can take
from the desired signal only specific values
 1.4 Signal Classification
– Continuous-time and discrete-time
Continuous: The signal can be described by functions of a continuous time
e.g. x(t) = e−|t| , for ∞<t<∞
Discrete: Signals are defined only at discrete values of time
e.g. x(tn) = e−|tn| , for n=0,±1,±2..

– Analog and digital

Analog: Signal whose amplitude can take on any value in a continuous range
Digital: Signal with finite values of amplitude

– Periodic and Aperiodic

Periodic : x(t)=x(t+To), the smallest value of To is the period of x(t)
Aperiodic: x(t) – no repetition, eg: audio signal

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Pengenalan Kepada Sistem Perhubungan
 g(t) g(t)

t
Analog, continuous-time Digital, continuous-time

g(t) g(t)

Analog, discrete-time Digital, discrete-time

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Pengenalan Kepada Sistem Perhubungan
Aperiodic signal: Unit pulse signal Periodic signal: A sinusoidal signal

An example of a periodic signal is a sinusoidal signal:

x(t )  A sin(2f ot   )

0  2f 0 ; T0  2  1
0 f0
sin (x+y) = sin x cos y + cos x sin y
2  2 
x(t  )  A sin 0 (t  )     A sin(0t  2   )
0  0 
 Asin(0t   ) cos(2 )  cos(0t   ) sin(2 )

But cos(2  ) =1 and sin(2  )=0 2

x (t  )  A sin(0t   )  x(t )
0

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Pengenalan Kepada Sistem Perhubungan
1.4.1 Harmonic signal
-A harmonic is a signal whose frequency
is an integral multiple of the frequency of
a reference signal.

-If f is the fundamental frequency, the 2nd

harmonic has frequency 2f, 3rd has 3f etc

-Nearly all signals have energy at harmonic

frequencies in addition to the fundamental

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1.5 Transmission Medium (Guided)
Kabel Terpiuh (Twisted pair)
– Unshielded Twisted Pair (UTP)
– Shielded Twisted Pair (STP)
Kabel Sepaksi (Coaxial)

Kabel Gentian Optik (Fiber Optic)

– Singlemode step index
– Multimode step index
– Multimode graded index
Pandu Gelombang (Waveguide)

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1.6 Transmission Medium (Unguided)

Ruang Bebas (Free Space)

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 Pengenalan Kepada Sistem Perhubungan
Representative
applications
Transmission

Propagation
designations

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Frequency
Wavelength

modes

Frequency
media
Optical Fiber

Laser beam

1015Hz
1.7 Frequency Spectrum

Ultraviolet
10-6m

Wideband data
Visible
Infrared
1014Hz
Extra High Satellite-satellite 1G0Hz
Frequency Microwave relay
EHF Earth-satellite
Waveguide
1cm

Line-of-sight

Super High Radar 10GHz

Frequency
radio

SHF
10cm

Broadband PCS
Ultra High Wireless communication 1GHz
Frequency Cellular, Pager
UHF
UHF TV
1m

Very High Mobil and Aeronautical

Frequency
VHF TV and FM 100MHz
Coaxial Cable

VHF
10m

Skywave
High Mobil radio

radio
Frequency
CB radio 10MHz
100m

HF
Amateur radio
Medium
Frequency
AM broadcasting 1MHz
MF
1km

Groundwave
Low
100kHz

radio
Frequency
Aeronautical
10km
LF
Submarine cable

Twisted Pair
Very Low Navigation

Cable
Frequency Transoceanic radio 10kHz
100km
VLF
Audio Telephone
Telegraph
1kHz
 1.8 Communication System Efficiency
• We can measure the level of efficiency of communication system
through several ways:
– How close the received signal to the transmitted input signal?
s(t), r(t) ; Needs high quality of transmission.
s(t) Analog – Signal to Noise Ratio (SNR).


s(t) Digital – Bit Error rate (BER).

– How much power needed to transmit modulated signal?
Low power; Lifespan of a battery is longer.
High power; Lifespan of a battery is shorter.
– How much Bandwidth, BW is needed to transmit the modulated
signal?
Low BW application means more users can share the
communication medium
– How much signal or signal size needs to transmit?
Analog system depends on s(t) BW.
Digital system depends on BW and bit rate, bit/s. 26
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1.8.1 Obstacle to Communication System

• Technology Problem
– Hardware
– Economy
– Law and Regulation

• Physical Problems
– BW
– Signal Power
– Noise

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 Important Parameters
• Bit Rate, fb = 1/Tb
– Important performance parameter for digital system
– The no of bits per second, inverse of bit duration
• 10 Gb/s bit rate, 0.1 ns bit duration
– Industry keeps demanding for higher bit rate due to user demands

• Bandwidth, B
– Range of frequencies
– Characteristics of an information signal, channel medium or devices
– E.g. voice (4 to 4 KHz), optical channel bandwidth (180 to 200 THz)
and LPF (0 to 500 KHz)
– B is related to fb
– Signal bandwidth depends on analogue or digital modulation
formats e.g. BAM = fm or 2fm , BNRZ= fb/2, BRZ= fb
– Bandwidth is a valuable resource in communication system
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• Channel capacity, C
– Maximum rate for information to be reliably transmitted over a noisy
communications channel
– C = B log2 (1 + S/N) {Shannon Limit}
B is channel BW and S/N is Signal to noise ratio
– For a given SNR, channel with higher bandwidth has higher capacity
– Medium (wireless/optical links) that has larger capacity can support
more users
 Unit dB in Communication
If P1 is the reference power: If V1 is the reference voltage:

 P2   V2 
PdB  10 log10   VdB  20 log10  
 P1   V1 
R1 does not have to = R2
 V2 
PdB  20 log10  
 V1  R1 = R2

1mw
average
dBm - Power measurement in unit mW i.e. P1 = 1 mW power of
telephone
transmitter
dBW - Power measurement in unit W i.e. P1 = 1 W

dBV – Voltage measurement in unit V i.e. V1 = 1 V

Purpose of using dB:
- shows ratio
- loss, gain and SNR of
a communication
system
- Power can vary Mwatt
from transmitter to
picowatt at receiver
input
- Easier working in dB
than absolute/linear
form

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> 1 mW

< 1 mW
 1.8.2 Types of Transmission
• Simplex
One way transmission
• Half-Duplex
Two way transmission but only one user can transmit the
signal at one time.
• Full-Duplex
Two way transmission, both users can transmit the signal at
the same time.

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Pengenalan Kepada Sistem Perhubungan
 1.10.4 Transmission Loss
• Attenuation is a major source of transmission loss
– Occurs along the transmission medium
• Will attenuate power and cause power loss => Pout < Pin.
 Power loss or power attenuation is given by:

Pin 1
L 
Pout G

 Pin 
LdB  10 log10    GdB
 Pout 
 Also can be calculated using :
LdB  
where:
l = length of the transmission medium
α = attenuation constant
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Pengenalan Kepada Sistem Perhubungan
 1.10.5 Attenuation
Transmission Medium Frequency Attenuation dB/km
Kabel Terpiuh (Twisted- 10kHz 2
pair Cable) 100kHz 3
300kHz 6
Kabel Sepaksi (Coaxial 100kHz 1
Cable) 1MHz 2
3MHz 4
Pandu Gelombang
Empat Segi (Rectangular 10GHz 5
Waveguide)
Kabel Fiber Optik (Fiber 3.6 x 1014Hz 2.5
Optic Cable) 2.4 x 1014Hz 0.5
1.8 x 1014Hz 0.2

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Pengenalan Kepada Sistem Perhubungan
Example 1.1
Calculate signal power if its value in dBm is 0 dBm.
dBm = 10 log P2 / P1 = 10 log P2 / 1 mW = 0
P2 = 1 mW

Example 1.2
Calculate signal power in dB if its value is 1 mW.

dB = 10 log P2 / P1 = 10 log P2 / 1 W = 10 log 1 mW / 1 W = - 30 dB

Example 1.3
A carrier signal, vc(t) = 100 cos 10t Volt was suppressed by 20 dB.
What is the carrier’s new amplitude?
dB = 20 log V2 / V1 = 20 log 100 / 1 = 40 dB
New carrier amplitude = 40 dB – 20 dB = 20 dB ;
20 log V = 20 dB ; V = log-1 1 = 10 Volt.
Therefore, vc(t)new = 10 cos 10t Volt 36
 1.9 Noise

• In practice, we cannot avoid the existence of

unwanted signal together with the modulated signal
transmitted by the transmitter.
• This unwanted signal is called noise.
• Noise is a random signal that exists in a
communication system.
• Random signal normally represented using
statistical properties e.g. PSD.
• The existence of noise will degrade the level of
quality of the receive signal at the receiver.

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Pengenalan Kepada Sistem Perhubungan
 1.9.1 Types of noise
• An undesired disturbance within the frequency band of interest; the summation
of unwanted or disturbing energy introduced into a communications system
from man-made and natural sources.

• A disturbance that affects a signal and that may distort the information carried
by the signal.

Noise

Internal Noise External Noise

Interference within a device or Man-made noise and

electronic circuit natural resources
• Thermal noise/Johnson noise • Lightning
•Random movement of • Solar noise
electrons within a conductor
due to thermal agitation • Ignition
• Shot noise • Crosstalk
• Random arrival of carriers
(electrons and holes) at the
output element of an electronic 38
device e.g. diode, transistor Pengenalan Kepada Sistem Perhubungan
 1.9.2 Noise Effect
• Degrade system performance for both analog and
digital systems.
• Receiver faces difficulties to understand the
original signal.
• Thus, receiver performance not optimum.
• Reduce the efficiency of communication system.

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 1.9.3 Thermal Noise
• Thermal noise is the Electronic noise - generated by the thermal
agitation of the charge carriers (the electrons) inside an electrical
conductor in equilibrium, which happens regardless of any applied
voltage.

• Movement of the electrons will form kinetic energy in the conductor

related to the temperature of the conductor.

• When the temperature increases the movement of free electrons will

increase and the current flows through the conductor.

• Current flows due to the free electrons will create noise voltage, n(t).

• Noise voltage, n(t) is influenced by the temperature and therefore it is

called thermal noise.

• Also known as Johnson noise or white noise or Nyquist noise.

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This type of noise was first measured by John B. Johnson at Bell Labs in 1928. He described his
findings to Harry Nyquist, also at Bell Labs, who was able to explain the results.

In 1928, J. B. Johnson proved that noise power generated is

proportional to the temperature and the BW.

Pn  TB
Pn  kTB Watt

where
Pn = noise power (Watt)
k = Boltzmann’s constant (1.38 x 10-23 J/K)
T = Temperature (K)
B = BW spectrum system (Hz)

Noise power can be modeled using voltage equivalent circuit (Thevenin

equivalent circuit) or current equivalent circuit (Norton equivalent circuit)

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It can be modeled by a voltage source representing the noise of the non-ideal
resistor in series with an ideal noise free resistor.

Vn, Noise
voltage source
Rn, Noise
=
source Rn, noise
free

(a) Noise source circuit (b) Thevenin equivalent circuit

• Noise source will be connected to a system with the input resistance RL.
• Therefore, total noise power is Pn.
• With the concept of maximum power transfer i.e when Rn = RL all the
power will be transferred to the load.
• Also called as impedance matching.

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Pengenalan Kepada Sistem Perhubungan
 Vn, Noise
voltage source
VL RL, system input
Rn, Noise resistance
free

(c) Thevenin equivalent circuit with the load

Given Rn  RL  R
Note: Vn = Vrms
Voltage across RL :
=> Vn2
RL 2  kTB
VL  Vn Vn  4R
Rn  RL VL2  2  Vn2 Vn2  4kTBR
=> PL   
Vn R R 4R
 Vn  4kTBR
2 and Pn  PL  kTB
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Pengenalan Kepada Sistem Perhubungan
 1.9.4 How to determine noise level in
communication system?
• Noise effect can be determined by measuring:
- Signal to Noise Ratio, SNR for analog system
- probability of error / bit error rate, BER for digital system

• To determine the quality of received signal at the receiver or an

antenna, SNRi is used.

• SNR o is always less than SNRi , due to the facts that the
existence of noise in the receiver itself. In the receiver usually
constitute a process of filtering, demodulation and
amplification.

• Other parameters that can be used are Noise Factor, F and

Noise Temperature, Te .

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Pengenalan Kepada Sistem Perhubungan
 1.10 Noise Calculation

• SNR is a ratio of signal power, S to noise power, N.

S
SNR  10 log dB
N
• Noise Factor, F
Si N i
F
So N o

• Noise Figure, NF NF  10 log F

Si N i
 10 log dB
So N o
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 1.10.1 Noise calculation in Amplifier
• To simplify the analysis the following noise model is used.
• - Amplifier with noise (Noisy Amp.)

G
Ni
Na
No
N o  GNNi  N a  GG( N i  NNai )
i
o
Nai
Noisy Amplifier

where N ai 
Na and Pn  N i  kTi B
G

Pengenalan Kepada Sistem Perhubungan

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 1.10.2 Analysis Amplifier Noise
Si
Ni+Nai
G So
No
(1) S o  GSi
N o  G N i  N ai 
Si SNRo  SNRi
(2) SNR Ni
i

SNRo GS i (3) We have:
G  N i  N ai  N i  kTi B and N ai  kTe B
N  N ai
 i kTe B
Ni => F  1 
N ai kTi B
 1
Ni Noise Factor: Noise Temperature:

Te  F  1Ti
N ai Te
F  1 F  1
Ni Ti 47
 1.10.3 Cascaded Connection
• In communication system cascaded connection is commonly
used:
• Below is the example of cascaded connection.

antenna
F1 , Te1 F3 , Te3
Si S1 S2
Ni N1 N2
G1 G3 So
Ti F2 , G2 , Te2
Nai1 Nai2 Nai3 No

pre-amplifier demodulator amplifier

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Pengenalan Kepada Sistem Perhubungan
Level 1: Si F1 , Te1 Level 2:
Ni S1 S1 S2
G1 F2 , G2 , Te2
Ti N1 N1 N2
Nai1 Nai2

S 2  G2 S1
S1  G1Si
N1  G1  N i  N ai1   G1G2 S i
 G1kTi B  G1kTe1 B N 2  G2 N1  N ai 2 
 G1kBTi  Te1   G1G2 N i  N ai1   G2 N ai 2
 G1G2 kTi B  G1G2 kTe1 B  G2 kTe 2 B
Level 3:  G1G2 kBTi  Te1   G2 kTe 2 B
F3 , Te3

S 0  G3 S 2
S2
G3 So
N2
Nai3 No
 G1G2G3 Si
N o  G3 N 2  N ai 3 
 G2G3 N1  N ai 2   G3 N ai 3
 G1G2G3kTi B  G1G2G3kTe1 B  G2G3kTe 2 B  G3kTe3 B
 G1G2G3kBTi  Te1   G2G3kTe 2 B  G3kTe3 B
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 SNRi
Ftot  
SNRo
Si
Ni

So
No
Si
kTi B

G1G2G3 S i
G1G2G3 kBTi  Te1   G2G3 kTe 2 B  G3 kTe 3 B
G1G2G3 kBTi  Te1   G2G3 kTe 2 B  G3 kTe 3 B

G1G2G3 kTi B
Ti  Te1 T Te 3
  e2 
Ti G1Ti G1G2Ti
Te1 T Te 3
 1  e2 
Ti G1Ti G1G2Ti

We have:
T
F  1 e
Therefore:
Ftot  F1 
F2  1  F3  1
Ti G1 G1G2 50
 Friss’s Formula:

Total Noise
Ftot  F1 
F2  1  F3  1  ...  Fn  1
Figure:
G1 G1G2 G1G2 ...Gn 1

Total Noise Te  F  1Ti

Temperature
Te 2 Te 3 Tn
Tetot  Te1    ... 
G1 G1G2 G1G2 ...Gn 1

CAUTION!!!!!!!!!!!
-This formula works in linear.
-Values e.g. SNR, F, loss, gain
etc are normally given in dB!
(need to convert to linear first)
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Example 1.4
One operational amplifier with a frequency range of (18-20) MHz has
input resistance 10 k. Calculate noise voltage at the input if the
amplifier operate at ambient temperature of 270C.

Vn2 = 4KTBR
= 4 x 1.38 x 10-23 x (273+ 27) x 2 x 106 x 104
Vn = 18 volt

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 Example 1.5
Noise generated in amplifier of 5 MHz bandwidth is represented by
amplifier input noise power of 0.082 pW. Calculate noise factor and
noise figure if the amplifier was fed with the
(a) source input signal match the temperature of 300 K
(b) source input signal match the temperature of 100 K

Ni No

(a) Noise power from the source input = KTiB

= 1.38 x 10-23 x 300 x 5 x 106 Ne = 0.082PW

= 0.021 pW

Ni  Ne 0.021 0.082 0.103

Noise Factor     4.9
Ni 0.021 0.021

Noise figure = 10log10 4.9 = 6.9 dB

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 Ni No
(b) Noise power from the source input = KTiB
= 1.38 x 10-23 x 100 x 5 x 106
= 0.007 pW Ne = 0.082PW

Ni  Ne 0.007  0.082 0.103

Noise factor     12.7
Ni 0.007 0.007

Noise Factor = 10log10 12.7 = 11.04 dB

Noise factor and noise figure were higher when operated at

lower room temperature, suggesting SNRi is much larger than
SNRo compared to the previous case

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Example 1.6
An antenna is connected to an amplifier with noise temperature, Te = 125 oK,
gain, G = 108. Given the bandwidth, B = 10 MHz and output receiver noise, No
= 10 W. Determine the antenna temperature, Ti and noise factor, F of the
receiver.

N o   N i  N e G
 KTi B  KTe B G
 KB Ti  Te G
10  1.38  10  23  10  106 Ti  125108
 Ti  600 o K

Te 125 N i  N e 100
F  1  1  1.2 or F   1.2
Ti 600 Ni 82.8

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Example 1.7
Three amplifiers, ABC was connected in series. Noise figure and power
gain of the amplifiers are given below:
Amplifier A : GA = 20 dB FA = 3 dB
Amplifier B : GB = 10 dB FB = 5 dB
Amplifier C : GC = 5 dB FC = 10 dB
An input signal of 50 dB higher than noise level was fed at the input of the
network. Calculate:
(a) Total noise factor
(b) SNR at the output

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Solution:
Amplifier A : GA = 20 dB FA = 3 dB
F  1 F3  1
F  F1  2  Amplifier B : GB = 10 dB FB = 5 dB
G1 G1G 2
Amplifier C : GC = 5 dB FC = 10 dB
10  1 10  1
5 / 10
 103 10  
100 100  10
3.16  1 10  1
 1.99   A B C
100 1000
 1.99  0.0216  9  10 3
 2.03
(a) Noise Factor = 10 log10 2.03 = 3.05 dB

(b) Di beri, SNRin = 50 dB

SNR input
F
SNR output
FdB = SNR in (dB) – SNR out (dB)
SNR out = 50 dB – 3.05 dB = 46.95 dB 57
 1.11 Noise in Modulation Systems
• To compare different modulation techniques, approach is from
system level, previously it is analyzed from circuit level
• Noise is modeled as Additive White Gaussian Noise
Additive
Random noise, n(t) is usually additive, it adds to the information signal, S(t).

S(t) + yo (t)= S(t) + n(t)

n(t)

White Constant PSD for all frequencies

Noise Uniform

Freq
Gaussian
Noise voltage amplitudes are assumed to have a Gaussian distribution.
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 Terms and Definitions
Gaussian probability density function (pdf)

X is the random variable, m is the mean of the distribution, s 2 is the

variance.

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 Autocorrelation and Power Spectral
Density
• Finding the frequency content of a random process. Define
autocorrelation at times t1 and t2 as

• Average power of a waveform is the mean square, Hence

• PSD – shows distribution of power of random signal with
frequency

• The average power can be found by integrating the PSD

• Extremely important PSD in communication, is the one

constant over all frequencies, also known as white noise

Ƞo

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 Band-limited Noise
• Any communication system that uses modulation typically
have a bandpass filter at the front end of the receiver.

• Function of the BPF – sufficiently allow modulated signals of

interest, restrict noise.
• If white noise with PSD of N/2, passed through such a filter,
then the PSD that enters the receiver is given by

Ƞo/2
Ƞo/2
N/2

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 Bandpass Representation of the noise
• It can be shown that

• For zero-mean Gaussian Process, Power = variance.

Lathi, pg. 514

Pn= Pc= Ps

63
• Thus, the average power in each waveform nc(t) and ns(t) is
identical to the power of the bandpass noise, n(t)

• The PSD of nc(t) and ns(t) is given by

N
Ƞo/2

Ƞ
No

• Which is equal to the PSD of n(t).

• The bandpass model of noise will be used for SNR
comparisons in later chapters
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HOMEWORKS (Discuss next Thursday)

1.Define the following terms

1. Modulation
2. Modulating signal
3. Modulated Signal
4. Modulation index
2.With the aid of block diagram, describe the generation of a
Double Side-band Full Carrier (DSCFC) AM signal.
3.Sketch the waveform and frequency spectrum of DSBFC
modulated signal

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