Dr. Ahmed El-Mahdy COMM 601: Modulation I
COMM 601: Modulation I
Prof. Ahmed El-Mahdy,Dean of the Faculty of IET
The German University in Cairo
Dr. Ahmed El-Mahdy COMM 601: Modulation I
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.
Dr. Ahmed El-Mahdy COMM 601: Modulation I
COMM 601: Modulation I• Instructor: Prof. Ahmed El-Mahdy
• Office : C3.319
• Lecture Time: Tuesday, 4th slot
• Email: [email protected]
Dr. Ahmed El-Mahdy COMM 601: Modulation I
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%
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Course Contents
SubjectNo.
Introduction1
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 & Equalization7
Dr. Ahmed El-Mahdy COMM 601: Modulation I
COMM 601: Modulation I
Lecture 1
- Introduction & Revision- Hilbert Transform
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Remember: Elements of Communication System
• 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
Dr. Ahmed El-Mahdy COMM 601: Modulation I
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).
Dr. Ahmed El-Mahdy COMM 601: Modulation I
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.
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Channel
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Fundamental Concepts
There are TWO basic modes of communication:
(1)Broadcasting:
- Use of a single powerful transmitter and several receiver (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.
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Main Recourses 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
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Remember : Effect of multiplying by exponential
tfj cetxty2
)()( )()( cffXfY
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Remember : Effect of multiplying by )2cos( tfc
)2cos()()( tftxty c )()(2
1)( cc ffXffXfY
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Analog Signals
- Used in:
- Radio broadcasting
- TV
- Microwave Communications.
•
• Analog Signals more affected by noise than digital (noise is part of the signal).
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Example: Analog Signals
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Signal Frequencies
around 6MHz
Quality
Dr. Ahmed El-Mahdy COMM 601: Modulation I
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
Dr. Ahmed El-Mahdy COMM 601: Modulation I
• 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:
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Remember: Definition of Bandwidth
Bandwidth is a term used to describe
a positive frequency range over which
the signal has significant content.
Absolute Bandwidth:
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Bandwidth - BasebandRemember
Absolute Bandwidth=W
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Bandwidth - BandpassRemember
Absolute Bandwidth=2W
Dr. Ahmed El-Mahdy COMM 601: Modulation I
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
Dr. Ahmed El-Mahdy COMM 601: Modulation I
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 Signal
3. Better control of filtering operation
Dr. Ahmed El-Mahdy COMM 601: Modulation I
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
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Other Representations
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Relationship Between the Three Forms
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Types of Continuous Wave Modulations
Digital Modulations Analog Modulations
- AM (DSB, SSB,..)
- FM
- PM
- ASK
- FSK
-PSK
-QAM
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Analog Modulations
Linear Modulation schemesAngle Modulation
AM: DSB, SSB,
and VSBFM
PM
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Parameters of Analog Modulation
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Hilbert Transform
d
tx
)(1
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Hilbert Transform
(From Signals & Systems)
Dr. Ahmed El-Mahdy COMM 601: Modulation I
Examples on Hilbert Transform