EE 372 – Communication Theory and Systems I

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ةبيط ةعماج

EE 372 – Communication Theory and Systems I

Lecture 1: Introduction

Omar Siddiqui

Department of Electrical Engineering College of Engineering

Taibah University Madinah

Email:[email protected]

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- Communication is the process of sending and receiving the information between two points which are separated by some distance

- As Electrical Engineers we are interested in “Sending and receiving

information between two points which are separated by some distance by using electromagnetic signals with minimum errors ”

College of Engineering, Taibah University

EE 372 Communication Theory

Why do we need the Communications?

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History – Communications Before the electronic age

Information transferred by pigeons

Information transferred by smoke

Information transferred by drum beat

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History– Evolution of Communications

Wireless

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Important Historical Moments

• 1844 Telegraph:

• 1876 Telephony:

• 1904 Radio:

• 1923-1938 Television:

• 1936 Armstrong’s case of FM radio

• 1938-1945 World War II Radar and microwave systems

• 1948-1950 Information Theory and coding. C. E.

Shannon

• 1962 Satellite communications begins with Telstar I.

• 1962-1966 High Speed digital communication

• 1972 Motorola develops cellular telephone.

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Telegraph (1830 - 1844)

Contributions in developing Telegraph

Joseph Henry (1830) – Sent electric current over one mile to activate an electromagnet William Cooke and Charles Wheatstone (1837) –

Samuel Morse (1844) – Invented Morse Code

Morse Code How does it work?

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Telephone (1876 by Alexander Graham Bell)

Bell in 1892 in New York calling Chicago

Bell to his Assistant Thomas Watson:

"Mr. Watson--come here--I want to see you."

First Telephone Conversation (March 10, 1876)

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Radio (1904)

Ampere, Faraday, Maxwell, Hertz, Marconi

Commercial Radio Inventor - Marconi

Marconi

Trans- Atlantic Radio

Antennas used by Marconi

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History

1923-1938 Television:

1936 Armstrong’s case of FM radio

1938-1945 World War II Radar and microwave systems 1948-1950 Information Theory and coding. C. E. Shannon 1962 Satellite communications begins with Telstar I.

1962-1966 High Speed digital communication 1972 Motorola develops cellular telephone.

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Examples of Communication Systems

ellular Communications

EE242 Signals and Systems

Radar

Wireless Internet

GPS Optical Communications

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Blocks of a Basic Communication system

Output message

Input message

Input Transducer

Transmitter Channel Receiver

Output Transducer Message signal or

baseband signal

Transmitted

signal Received signal Output baseband signal

Examples: Radio Channel: Air

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Transmitter Channel Receiver

Output Transducer Message signal or

baseband signal

Transmitted

Examples: Optical Channel: Fiber

Blocks of a Basic Communication system

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First Stage (Input Transducer)

Electric signal

Time (t) V(t)

Voltage

Transmitter Channel Receiver Output

Transducer Message signal or

baseband signal

Transmitted

Transducer: Converts input message to electric signal. Examples:

-Keyboard - Mic

- Camera

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Second Stage (Transmitter)

Input

Transducer Transmitter

Transmitter: A transmitter makes the signal suitable for the channel. It can do following:

- Modulation (Transforms a low frequency signal to a high frequency signal) - In a digital systems, it also does:

- Analog to digital conversion - Digital modulation

- Coding

Message or baseband signal

Transmitted signal

Analog Transmitter

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Second Stage (Transmitter)

Transmitter: A transmitter makes the signal suitable for the channel. It can do following:

- Modulation (Transforms a low frequency signal to a high frequency signal) - In a digital systems, it also does:

- Analog to digital conversion - Digital modulation

- Coding

A/D Coding Modulator

Message or baseband signal (analog)

Baseband signal (digital)

Coded signal

Digital Transmitter

Transmitter

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The Signals in the Communication system

Transmitter Channel

Message signal or baseband signal

Received signal

Time Domain

t m(t)

Frequency Domain

(bandwidth) _M(f)

t s(t)

B

S(f)

2B

t s(t)

Modulation and Bandwidth

Fourier Transform

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The Signals in the Communication system

t s(t)

Receiver Output

Transducer

Output baseband signal

m_o(t)

m(t) m_o(t)

Comparison between input and output

Output signal is distorted because of channel effects like noise and bandwidth

Effect of Channel

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1. Ease of Radiation

The size of antenna depends on the size of the wavelength. Without modulation, the baseband speech signals are in the range of 100 to 3000 Hz i.e.

 Thus antenna sizes would be impractical.

 For a 3MHz frequency signal, the wavelength is about 100m. So the antenna sizes become practical. For example a half wave dipole is 50m

f km

c 3000

3000 10 3 ⁸

 



 

Why Modulation?

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Why Modulation?

2. Multiplexing of Signals

Multiple signals with same frequency spectrum cannot be transmitted on the same channel. (Interference)

 Modulation allows several signals having different frequencies to be transmitted on the same channel

Frequency MUX

f₁ f₂ f₃ f₄ f

f₁ f

f₂ f

f₃ f

f f

4

Frequency DEMUX

f₁ f

f₂ f

f₃ f

f f

4

Frequency Division Multiplexing

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Why Modulation?

3. Exchange of Bandwidth and Signal to Noise Ratio (SNR)

Modulation can increase the bandwidth of the signal which reduces the requirement of SNR. (Shannon’s Theorem)

4. Availability of more fractional BW

Fractional BW is defined as:

 Higher frequencies result in less fractional BW

 Hardware costs are less if this is kept within 10%

Frequency Carrier

BW Baseband

BW Fractional 

S(f)

2B

S(f)

2B

f1 f2

1 1

2 f FBW  B

2 2

2 f FBW  B

1

2

FBW

FBW 

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Different Types of Modulations

Amplitude modulation

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Different Types of Modulations

Frequency modulation

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Example of a Modulated Signal (Cellular Signal)

Input Message

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Digital Communication System Analog Communication System Advantage :

 inexpensive digital circuits

 privacy preserved (data encryption)

 can merge different data (voice, video and data) and transmit over a common digital transmission system

 error correction by coding

Disadvantages :

 expensive analog components : L&C

 no privacy

 can not merge data from diff. sources

 no error correction capability

Disadvantages :

 larger bandwidth

 synchronization problem is relatively difficult

Advantages :

 smaller bandwidth

 synchronization problem is relatively easier

Comparisons of Digital and Analog Communication Systems

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What does a Communication Engineer Study?

Modulation Theory:

-Sinusoidal Modulation: Amplitude, Frequency, and phase are modified by a signal that carries the information

- Pulse Modulation: Amplitude, Width, or position of a periodic pulse is modified by a signal that carries some information

Sinusoidal Modulation Pulse Modulation

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What does a Communication Engineer Study?

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What does a Communication Engineer Study?

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Course Outline and Textbook

Introduction to Digital Modulation Schemes 1

Pulse Code modulation. 3

Pulse Analog Modulation 2

Angle Modulation 3

Amplitude Modulation 3

Representation of bandpass signals and systems 1 Transmission of signals through linear systems

(Fourier Transforms an Series)

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Course Content Weeks

Textbook:

B.P. Lathi, “Modern Digital and analog Communication Systems”, 4^th Edition

6. Final Exam 40%

5. Laboratory 20%

4. Mid Term Exam 2 15%

3. Mid Term Exam 1 15%

2. Quizzes 5%

1. Class participation and homework 5%

Grading