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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Comm 502: Communication Theory
Prof. Dr. Ahmed El-MahdyDean of the faculty of IET
The German University in Cairo
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
COMM 502: Communication Theory
• Instructor: Ahmed El-Mahdy
• Office : C3.319
• Lecture Time: Sat. 2nd Slot
• Office Hours: Sunday (12am-4 pm)
• Email: [email protected]
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Text BookText Book:
• B. Sklar, Digital Communications: Fundamentals and Applications, Prentice Hall, 2001
Reference Book:
* Leon Couch II, Digital and Analog Communication Systems, 7th edition, Prentice-Hall, 2007
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Grading
• Quizzes 15%
• Assignments 15%
• Practical Assignment 10%
• Midterm Exam 25%
• Final Exam 35%
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Course ContentsSubjectNo
Basic Concepts of Communications: Elements of a communication system, channel
impairments, baseband and band-pass signals, noise, random variable, probability density
function, Gaussian distribution.
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Transmission of Baseband Signals:
Pulse amplitude modulation: Sampling: impulse sampling, natural sampling, and flat-top
sampling. Pulse code modulation: quantization, coding: Line codes.
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Introduction to Source Coding:
Information sources, discrete sources, introduction to information theory, properties of source
coding, source coding theorem, Huffman code, Lempel-Ziv Coding ,..
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Shannon Information Theory:
Information measure, entropy, mutual information, noise, ..
channel capacity: Binary symmetric channel, binary eraser channel, Shannon Theory,..
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Introduction to channel coding: Types of error control, channel models, code rate and
redundancy, Hamming codes.
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Comm 502: Communication Theory
Lecture 1
- Basic Concepts of communications:
Elements of the communication system,Channel impairments, noise,
baseband and band-pass signals, random variable, probability density function,
Gaussian distribution
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Elements of Communication System
Elements for any Communication System:
- Transmitter
- Channel
- Receiver
Transmitter Channel Receiver)(tm )(~ tm
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
• A communication system consists of three main blocks:
Transmitter: modifies the signal for efficient transmission.
Channel: medium in which the modified signal is sent. The channel acts as a linear filter.
Receiver: reprocesses the signal to get estimate of the transmitted signal.
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Channel impairments
– Noise:Unwanted signals that disturb or contaminate the
desired signals. For ex. thermal noise, ..
– Interference:
Is the mixing of the transmitted signal with another signal. This interfering signal carries information from another source to another destination.
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Channel impairments
-Jamming:• A strong signal, not carrying information transmitted on
the same channel with the aim of disturbing communications. Intended to prevent reception at the required destination (in Military applications).
– Distortion: • Is a change in the transmitted signal due to the non-
ideality of the channel.
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Channel impairments
– Fading:• Change in signal amplitude and phase due to motion
and scattering.
• The receiver may receive multiple copies of the signal with short spacing.
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Communication System Parameters
1. Quality of transmission:
How close is the estimate to the original signal m(t)?
- Better estimate =higher quality transmission
We measure the quality by:
- Analog: Signal-to-noise ratio (SNR) - Digital : Bit Error Rate (BER)
2. Power:
How much power is required to transmit s(t)?
• Lower power=longer battery life, less interference
3. Bandwidth:
How much bandwidth is required to transmit s(t)?
• Less BW means more users can share the channel
)(~ tm
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Baseband and bandpass Signals
• Baseband Signal: Has its spectrum centered around the origin f=0 and is zero elsewhere.
- fm 0 +fm
W(f)
f
baseband Signal
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
• Bandpass Signal: Has its spectrum shifted to a
higher frequency (carrier frequency ),
Its frequency content is centered around .
0
)( fW
2
ccc ffWffWtftw 2
12cos
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Modulation
Modulation Types
Analogue
Modulation
Digital Modulation
bit stream (1 0 0 0 0 1 1)
What is Modulation?
•Modulation is varying the parameters of signal
transmission in accordance to the information to be
transmitted
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Communication SystemsDigital
– Finite set of messages (signals)
– Privacy & security (ease of encryption)
– Error detection and correction.
– More bandwidth– More overhead– Synchronization is required – Need for A/D and D/A
converters
Analog
- Continuous set of messages (signals).
– More affected by noise than digital (noise is part of the signal)
Disadvantages:
Disadvantages:
Advantages:
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Performance measure
• Analog communications:
Output signal to noise ratio:
• Digital communications:
Probability of error:
BandwidthsignalinpowerNoise
powerSignalSNR
bits ed transmittofnumber total
errorin bitsP e
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Definitions of Bandwidth
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Example 1:
Example 2:
?
??
[Hz]
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Example 1:
Example 2:
[Hz]
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Example 1:
Example 2:
[Hz]
?
?
9.1 kHz 10.9kHz
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Example 1:
Example 2:
[Hz]
10.9-9.1=1.8kHz
9.1 kHz 10.9kHz
12-8=4 kHz
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
White Noise• A white noise process has a flat PSD over a wide range
of frequencies:
is called the height of the power spectral
density of the noise .
2
oN
2)( o
w
NfS
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Dr. Ahmed El-Mahdy
Communications DepartmentComm 502: Communication Theory
Ex: White Noise With zero mean
Time domain representation