comm 502: communication theory - guceee.guc.edu.eg/courses/communications/comm502 communication...

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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


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]

mailto:[email protected]

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Dr. Ahmed El-Mahdy


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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Grading

• Quizzes 15%

• Assignments 15%

• Practical Assignment 10%

• Midterm Exam 25%

• Final Exam 35%

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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.

2

Introduction to Source Coding:

Information sources, discrete sources, introduction to information theory, properties of source

coding, source coding theorem, Huffman code, Lempel-Ziv Coding ,..

3

Shannon Information Theory:

Information measure, entropy, mutual information, noise, ..

channel capacity: Binary symmetric channel, binary eraser channel, Shannon Theory,..

4

Introduction to channel coding: Types of error control, channel models, code rate and

redundancy, Hamming codes.

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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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Elements of Communication System

Elements for any Communication System:

- Transmitter

- Channel

- Receiver

Transmitter Channel Receiver)(tm )(~ tm

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• 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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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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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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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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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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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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• 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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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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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


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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Definitions of Bandwidth

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Example 1:

Example 2:

?

??

[Hz]

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Example 1:

Example 2:

[Hz]

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Example 1:

Example 2:

[Hz]

?

?

9.1 kHz 10.9kHz

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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


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


Ex: White Noise With zero mean

Time domain representation

comm 502: communication theory - guceee.guc.edu.eg/courses/communications/comm502 communication...

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