Post on 04-Jun-2018
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Communication
Technologies
Modulation and Multiplexing
Week #3ICS620
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Overview
Frequency Spectrum
Modulation techniques Multiplexing--TDM vs FDM
Multiple Access Signal formats
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The Bands
VLF LF MF HF VHF UHF SHF EHF
Submillimeter
Range
ELF
3MHz 30MHz300MHz 3GHz 30GHz 300GHz
Far
Infra-
Red
300KHz30KHz 3THz
300mm
Radio Optical
3KHz
Near
Infra-
Red
700nm
1PetaHz
R
e
d
O
r
a
n
g
e
Y
e
l
l
o
w
G
r
e
e
n
B
l
u
e
I
n
d
i
g
o
V
i
o
l
e
t
600nm 400nm500nm
Ultraviolet
1ExaHz
X-Ray
1500nm
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Frequency Spectrum
Limited resource
Managed WARC
FCC
Bands
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Modulation Techniques
Amplitude Modulation
Frequency Modulation Phase Modulation
Pulse Modulation
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Amplitude Modulation
Uses a higher frequencycarrier
Most efficient use offrequency
Time and Frequency Domain Susceptible to Noise
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Most Efficient Use of
Frequency
Maximum frequency required
is: Twice baseband
Just baseband (specialconditions)
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Higher Frequency Carrier
Signal
Carrier
time
time
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Higher Frequency Carrier
Power Spectral Density
frequency
SignalCarrier
Baseband
watts
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Time Domain
Signal
Carrier
time
time
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Time Domain Continued
time
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Detection of Signal
time
time
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Frequency Domain
Unmodulated
frequency
SignalCarrier
Baseband
watts
Modulated
frequency
Signal
Carrier
Baseband
watts
Baseband
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Spectrum of AM signal
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Susceptible to Noise
time
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Carrier Signal
Oscillator
Information
Signal
Modulation
Device
Low-Power
Amplifier
Final Amplifier
Antenna
Simple block diagram of
AM modulation
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Single Sideband (SSB)
Variant of AM is single sideband (SSB) Sends only one sideband
Eliminates other sideband and carrier
Advantages Only half the bandwidth is required
Less power is required
Disadvantages Suppressed carrier cant be used for
synchronization purposes
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Frequency Modulation
Uses a higher frequency
carrier
Usually more bandwidth
Time and Frequency Domain
Resistant to some Noise
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Time Domain
Signal
Carrier
time
time
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Time Domain
time
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Frequency Domain
Unmodulated
frequency
SignalCarrier
Baseband
watts
Modulated
frequency
Signal
Carrier
watts
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Resistant to Some Noise
time
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Phase Modulation
Uses a higher frequencycarrier
Fairly efficient use offrequency
Time and Frequency Domain Used mainly for data
Ti D i
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Time Domain
(Instantaneous View)
Unmodulated Carrier
Modulated Carrier
Phase
Input
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Phase Shift Keying
Time Plot
0
O
90
O
180
O
270
O
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Pulse Modulation
Uses the sampling rate
PAM PDM, PWM
PPM PCM
S i h S li
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Starts with Sampling
Volts
time
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PAM
Volts
time
Pulse Amplitude Modulation
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PDM (a.k.a. PWM)
Volts
time
max = largest Positivemin = largest Negative
time
Pulse Duration Modulation (Pulse Width Modulation)
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PPM
Volts
time
max = largest Positive
min = largest Negative
time
Pulse Position Modulation
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Pulse Code Modulation
By quantizing the PAM pulse, originalsignal is only approximated
Leads to quantizing noise
Signal-to-noise ratio for quantizing noise
Thus, each additional bit increases SNR by6 dB, or a factor of 4
dB76.102.6dB76.12log20SNRdB nn
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PCM
Volts
time
time
01000 01000
8 8
-2
-9
-1
5
-7
10010 11001 10001 00101 10111
Pulse Code Modulation
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Multiplexing
Frequency Division
Multiplexing
Separate each basebandsignal into a discrete band
Uses AM-SSB/SC to positioneach baseband
F Di i i M lti l i
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Frequency Division Multiplexing1
2
3
4
frequency
frequency
frequency
frequency
frequency
1 2 3 4
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Multiplexing
Time Division Multiplexing
Separate each digitalbaseband into discrete time
slots
Cyclical in nature
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Time Division Multiplexing
1
2
3
4
Rotation Analogy
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FDMA
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FDMA
Frequency Division Multiple Access
F
requency
Time
Chan A
Chan B
Chan C
Chan D
TDMA
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TDMA
Time Division Multiple Access
F
requency
Time
Chan A
Chan B
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Summary
Frequency Spectrum
Modulation techniques--AM,
FM, Phase, and Pulse
Modulation
Multiplexing--TDM vs FDM