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EE4900/EE6720 Digital Communications Suketu Naik
EE4900/EE6720: Digital Communications
Lecture 4
Analog Modulation
2
EE4900/EE6720 Digital Communications Suketu Naik
Block Diagram of Communication System
Generic Communication SystemQualcomm MDM9635M LTE Modem in iphone6
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EE4900/EE6720 Digital Communications Suketu Naik
Analog Communication System
Informatio
n (sound,
video, text,
data, …)
Transducer &
A/D Converter Modulator
Output
Signal
D/A Converter
and/or output
transducer
Demodulator LNA,
Filter,
etc.
Channel
= Focus of this lecture
Block Diagram of Communication System
Power
Amplifier +
Filter etc.
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EE4900/EE6720 Digital Communications Suketu Naik
Basics of Modulation
Wave Equation of the Carrier
Can manipulate either the amplitude, or the
frequency or the phase to carry the information
Amplitude Modulation (AM): Change Amplitude of the Carrier Wave
Frequency Modulation (FM): Change Frequency of the Carrier Wave
Phase modulation (PM): Change Phase of the Carrier Wave
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EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Amplitude Modulation (AM)
Information
(baseband signal at
lower frequency)
Carrier signal
at higher
frequency
Up-converted
Baseband
Signal
Simulink Model (In-class exercise)
Hardware Demo (N/A)
Ref: Data Communications, Kwangwoon University
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EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Amplitude Modulator Circuit
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EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Amplitude Modulation (AM) Equations
m(t)=analog or digital data to be
transmitted=modulating signal
s(t)=output signal=modulated
carrier wave
Ac=RMS level [V]
fc=carrier frequency [Hz]
How can we de-modulate the transmitted AM signal?
Amplitude of the carrier
Wave is modulated
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EE4900/EE6720 Digital Communications Suketu Naik
AM Demodulation Technique
Local
Oscillator
Received
Signal
Mixer
(Multiplier)
Low
Pass Filter
Basic Analog Modulation Schemes
Remove
DC
Demodulated
Signal
Same Frequency
As the Carrier Signal
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EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Frequency Modulation (FM)
Information
(baseband signal at
lower frequency)
Carrier signal
at higher
frequency
Up-converted
Baseband
Signal
Simulink Model (In-class exercise)
Hardware Demo (N/A)
Ref: Data Communications, Kwangwoon University
10
EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Frequency Modulator Circuit
11
EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Frequency Modulation (FM) Equations
m(t) (=m(σ))=analog or digital data to be
transmitted=modulating signal
Df=frequency deviation constant [rad/V-s]
Ac=amplitude level [V]
fc=carrier frequency [Hz]
How can we de-modulate the transmitted FM signal?
Frequency of the carrier
wave is modulated
12
EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
FM Demodulation Technique (in DSP!)
Ref: https://www.veron.nl/wp-content/uploads/2014/01/FmDemodulator.pdf
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EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Phase Modulation (PM)
Information
(baseband signal at
lower frequency)
Carrier signal
at higher
frequency
Up-converted
Baseband
Signal
Ref: Data Communications, Kwangwoon University
14
EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Phase Modulation (PM)
Binary Phase Shift Keying (BPSK)
15
EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Phase Modulator Circuit
16
EE4900/EE6720 Digital Communications Suketu Naik
Basic Analog Modulation Schemes
Phase Modulation (PM) Equations
m(t)=analog or digital data to be
transmitted=modulating signal
Df=frequency deviation constant [rad/V-s]
Ac=amplitude level [V]
fc=carrier frequency [Hz]
How can we de-modulate the transmitted PM signal?
Phase (and frequency) of the
carrier wave is modulated
s(t)
m(t)
17
EE4900/EE6720 Digital Communications Suketu Naik
Assignment 2 [20]
Simulate AM and FM Communication using Simulink
Submit the following:
1) Simulink models
2) Time-domain plots
3) Frequency domain plots