Communications Principles
(EE 322)
By
Dr. Eng. Omar Abdel-Gaber M. Aly
omar.aly@aun.edu.eg
Assistant Professor
Electrical Engineering Department
College of Engineering Al-Majmaa
Al-Majmaa University
Schedule & Instructors
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Schedule:
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/2D 025
/3D 039
Instructors: Dr. Omar Abdel-Gaber
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Mon 10:00 – 12:00
We 9:00 – 10:00
(omar.aly@aun.edu.eg)
Office hours: sat (12:0-13:0pm), Mon(12:0-13:0pm),
or by appointment.
Research areas: Wireless Communication.
TAs:


Eng.
Office hours: As indicated in Students Schedule
Communications Principles, Dr. Omar Aly
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Recommended Texts
1- “Introduction to Analog and Digital Communications”
Author: S. Haykin, M. Moher 2007
2- “Modern Digital and Analog Communications Systems”
Author: B P Lathi, 1998
3- “Communication Systems” Author: Simon Haykin, 2001
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Grading
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EE 322 Grade breakup:
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First Midterm exam :
25 (25%)
Second Midterm exam :
25 (25%)
Home Work:
5 (5%)
Quiz:
5 (60%) Total 60
Extra Grade:
5 (5%)
 Mimi Project (Hardware Implementations):
(groups of maximum 3 Persons are allowed)
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First Midterm exam:
Second Mid exam:
Communication Principles, Dr. Omar Aly
MATLAB Simulink
Homework includes some MATLAB
programming and Simulink assignments.
 Simulink:
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A block diagram-based MATLAB extension that
allows engineers to rapidly and accurately
build computer models of dynamic systems.
Simulink is a programming language itself.
The simulink diagrams can be converted to C
codes, which can be compiled for different
target platforms.
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An Example of Simulink
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Type “simulink” from MATLAB command line to
launch the simulink window.
A short tutorial will be distributed with the first
Simulink assignment.
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Content of the Course
 Analog
Communications
 Linear modulation: AM, SSB, VSB
 Angle modulation: PM and FM
 Pulse modulation
 Random processes
 Autocorrelation
 Power spectral density
 Effect of noise in analog communication
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Introduction
 What
is a communication systems ?
The function of a communication system is to
transfer information from one point to another
via some communication links.
 Examples of Communication Systems
 Postal System
 Cellular System
 Television & Radio
 Home Telephone System
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Block Diagram of a Comm System
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Input message may not be suitable for transmission directly
 e.g., may need to be compressed
Transmitter: make the signal suitable for transmission
 By modulating a carrier signal: change its amplitude, phase, or
frequency
Channel: air, phone line, coaxial cable, power line, optical cable……
 Noise can be introduced during transmission
 Different channels and noises have different characteristics
Receiver: recover (demodulate) the message signal
 The transmitter and the receiver are jointly designed.
Modem: The combination of Modulator and Demodulator
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Types of Communications Systems
There are two basic types of communications
systems:
1.
Analog Communications Systems
2.
Digital Communications Systems
 It is necessary to introduce the concept of modulation
and demodulation.
Modulation is simply the process of changing one or
more properties of a high frequency analog signal
(called a carrier) in proportion with that of a low
frequency information signal.
Demodulation as you may have guessed is the reverse
of modulation.

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Analog Communications System
 An
analog communications system is a system
in which energy is transmitted and received in
analog form. In this system both the carrier
and the information are analog signals.
 An analog signal is a continuously varying
signal such as a sine wave.
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Simplified block diagram of an
analog communications system
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Modulation

The equation below is the mathematical
representation of a time-varying sine
wave such as a high frequency carrier.
x(t )  A sin( 2pft   )
x(t) = Instantaneous value
A
= Peak value
w
= Angular Frequency = 2pf

= Phase angle

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Modulation
If an analog information signal is use to:
• Vary the amplitude of the carrier in accordance to the
information signal. This is referred to as Amplitude
Modulation (AM).
• Vary the frequency of the carrier in accordance to the
information signal. This is referred to as Frequency
Modulation (FM).
• Vary the phase of the carrier in accordance to the
information signal. This is referred to as Phase
Modulation (PM) .
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Modulation
 Modulation
is performed in a transmitter by a
circuit called a modulator.
 A carrier that has been acted on by an
information signal is called a modulated wave
or modulated signal.
 Demodulation is performed in a receiver by a
circuit called a demodulator.
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Primary Resource and
Operational Requirements
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The two primary communication resources:
 Transmitter power
 Channel bandwidth
The performance of the system is also affected by the noise
Signal-to-noise ratio (SNR):
 Joint effect of the signal power and noise power
The design of a communication system is a tradeoff between SNR
and channel bandwidth.
To improve the performance of a system:
 If there is a limitation on bandwidth, we can increase the SNR
(easier)
 If there is a limitation on SNR, we can increase the bandwidth
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Electromagnetic Frequency
Spectrum
The purpose of communications system is to communicate
information between two or more locations commonly called
stations.
 This is accomplished by converting the information into
electromagnetic energy and then transmitting it to one or more
stations.
 Electromagnetic energy can propagate:
1. As a voltage or current along a metallic wire
2. As emitted radio waves through free space
3. As light waves down optical fiber
 Electromagnetic energy is distributed throughout an almost
infinite range of frequencies

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Electromagnetic Frequency
Spectrum
The electromagnetic frequency spectrum is divided
into subsections, or bands, with each band having a
different name and boundary.
 The International Telecommunications Union (ITU)
is an international agency, which is in control of
allocating frequencies and services within the overall
frequency spectrum.
 The total usable radio-frequency (RF) spectrum is
divided into narrow frequency bands, which are given
descriptive name and band numbers
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Electromagnetic Frequency
Spectrum
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Electromagnetic Frequency
Spectrum
Medium frequencies are signals in the 300-KHz to 3MHz range and are used primarily for commercial
AM broadcast (535 kHz to 1605 kHz).
 Very high frequencies are signals in the 30 MHz to
300-MHz range and are used for mobile radio,
commercial FM broadcasting (88 MHz to 108MHz).
 Ultrahigh frequencies are signals in the 300 MHz to
3GHz range and are used by cellular telephones, etc.
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Problem transmitting at low
frequency
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Interference
Large antenna
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Problem transmitting at low
frequency
 Electromagnetic
waves travel at the speed
of light
 = c/f
 c = 299 792 458 m / s
 Suppose f = 60 Hz
 Then  = 299792458/60
 = 4,996,540.97m
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