COMM 601: Modulation I - GUCeee.guc.edu.eg/Courses/Communications/COMM601... · COMM 601: Modulation I Lecture 1 ... - The communication process takes place over a link between a

Dr. Ahmed El-Mahdy COMM 601: Modulation I

COMM 601: Modulation I

Prof. Ahmed El-Mahdy, Communications Department

The German University in Cairo


Text Books

[1] Couch, Digital and Analog Communication Systems, 7th edition, Prentice Hall, 2007.

[2] Simon Haykin, Communication Systems, 4th edition, John Wiley & Sons, 2001.


COMM 601: Modulation I • Instructor: Prof. Ahmed El-Mahdy

• Office : C3.319

• Office Hours: Monday (12 am-5pm)

• Email: [email protected]

mailto:[email protected]


Grading

• Quizzes (3 Quizzes best 2) 20% (NO compensation Quizzes will be held)

• Assignments (2 Assignments best 2) 10%

• Project 5%

• Midterm Exam 25%

• Final Exam 40%


Course Contents

Subject No.

Introduction 1

Hilbert Transform 2

Linear CW Modulations (AM, DSB, SSB, & VSB) 3

Angle Modulations (FM & PM) 4

Noise in AM receivers. 5

Noise in FM receivers. 6

Channel Estimation & Equalization 7


COMM 601: Modulation I

Lecture 1

- Introduction & Revision - Hilbert Transform


: Elements of Communication SystemRemember

• The transmitter is located at some point in space

• The receiver is located at some other point separate from the

transmitter

• The channel is the physical medium that connects them


Transmitter • The purpose of the transmitter is to convert the

message signal produced by the source of information into a form suitable for transmission over the channel.

• One of the process performed by the transmitter is the MODULATION.

• MODULATION is the process of transformation of baseband signal m(t) into a passband signal s(t) using a carrier signal c(t).


Receiver • The purpose of the receiver is to recover the message

signal through demodulation.

• DEMODULATION is the inverse process of modulation i.e transformation of passband signal s(t) into the original baseband signal m(t).

• Some other tasks of the receiver are:

- Noise reduction

- Interference suppression.


Channel


Fundamental Concepts

There are TWO basic modes of communication:

(1)Broadcasting:

- Use of a single powerful transmitter and several receivers (ex.

broadcasting).

- Signals flow only in one direction.

(2) Point to Point:

- The communication process takes place over a link between a

single transmitter and a receiver.

- Signals flow in two direction.


Main Resourses of Communication Systems

• Transmitted Power: is the average power of the transmitted

signal.

• Channel Bandwidth: is the range of frequencies allocated to

the channel.

Performance measure • In Analog communications: Performance is measured by “output

signal to noise ratio” defined by:

BandwidthsignalinpowerNoise

powerSignalSNR


Effect of multiplying by exponential Remember :

tfj cetxty2

)()( )()( cffXfY


Effect of multiplying byRemember : )2cos( tfc

)2cos()()( tftxty c )()(2

1)( cc ffXffXfY


Analog Signals - Used in:

- Radio broadcasting

- TV

- Microwave Communications.

• Processing of analog signals: is simple in concept but difficult to build because of requirements on linearity and system adjustment. For example: voice communication requires non-linear distortion.

• Analog Signals more affected by noise than digital (noise is part of the signal).


Analog Signals Example:


Signal Frequencies

around 6MHz


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


• A carrier frequency is used to shift the frequency spectrum of transmitted signals.

• Baseband signals w(t) may be transformed into bandpass signals through multiplication by a carrier (Modulation):

ccc ffWffWtwtw 2

1cos

- fc 0 +fc

W(f)

f - fm 0 +fm

W(f)

f

Band Pass Signals:


Remember: Definition of Bandwidth

Bandwidth is a term used to describe

a positive frequency range over which

the signal has significant content.

Absolute Bandwidth:


Baseband -Bandwidth Remember

Absolute Bandwidth=W


Bandpass -Bandwidth Remember

Absolute Bandwidth=2W


The Reasons for Bandpass Modulation

1. To decrease size of Antenna

For efficient radiation of electromagnetic energy, the size of the

radiation antenna is proportional to the wavelength of the radiated

signal.

As f increases decreases and then Anntena size decreases

m/s103, 8 cf

cAntennaofSize


Consider the case of several radio stations broadcasting audio baseband

signals directly, without any modulation. They would interfere with each

other because the spectra of all the signals occupy more or less the same

bandwidth.

We can use various audio signals to modulate different carrier

frequencies, thus translating each signal to a different frequency range. If

the various carriers are chosen sufficiently far apart in frequency, the

spectra of the modulating signals will not overlap and thus will not

interfere with each other.

2. Simultaneous Transmission of Several Signals

. Better control of filtering operation3


Complex Envelope Representation • Any bandpass signal s(t) (modulated signal) can be

represented by:

• Where:

Re {.} represents the real part of any complex

number

is the angular frequency of the carrier signal

is called the complex envelope

tj cetCts

)(Re)(

c

)(tC

1


Other Representations


Relationship Between the Three Forms


Types of Continuous Wave Modulations

Digital Modulations Analog Modulations

- AM (DSB, SSB,..)

- FM

- PM

- ASK

- FSK

-PSK

-QAM


Analog Modulations

Linear Modulation schemes Angle Modulation

AM: DSB, SSB,

and VSB FM

PM


Parameters of Analog Modulation


Hilbert Transform

d

tx

)(1


Hilbert Transform

(From Signals & Systems)


Examples on Hilbert Transform

Documents

COMM 601: Modulation I - GUCeee.guc.edu.eg/Courses/Communications/COMM601... · COMM 601: Modulation I Lecture 1 ... - The communication process takes place over a link between a