COMM 601: Modulation I Lecture 5 Single Side Band Vestigial … · 2017. 3. 7. · COMM 601:...
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Dr. Ahmed El-Mahdy COMM 601: Modulation I COMM 601: Modulation I Lecture 5 Single Side Band Vestigial Side Band & Applications
Transcript of COMM 601: Modulation I Lecture 5 Single Side Band Vestigial … · 2017. 3. 7. · COMM 601:...
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
COMM 601: Modulation I
Lecture 5
Single Side Band Vestigial Side Band & Applications
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Time domain representation of SSB We use Hilbert Transform:
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Time domain representation of LSB
07.03.2017
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)()()( fMfMfM
)( j)(j)(ˆ fMfMfM
)(tm
)(ˆ tm
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Time domain representation of USB
Hilbert Transform:
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Time domain representation of SSB
Note the difference between
LSB and USB
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Three Forms of modulated signal representation of SSB
-ve for LSB and +ve for USB
Q
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Generation of Single Side Band (SSB) In SSB modulation, only the upper or lower sideband is transmitted. The first method
to generate the SSB modulation is the frequency discrimination method that
consists of two stages:
(1) The first stage is a product modulator which generates a DSB-SC modulated
wave.
(2) The second stage is a band-pass filter, which is designed to pass one of the
sidebands of this modulated wave and suppress the other.
MODULATING
SIGNAL
tm tftm c2cos
tfc2cosCARRIER
MODULATED
SIGNAL
tsBPF
)Frequency discrimination method:1(
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Generation of Single Side Band (SSB)
) Frequency discrimination method:1(
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Generation of Single Side Band (SSB) ) Frequency discrimination method:1(
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Generation of Single Side Band (SSB)
) Balanced Modulator:2(
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Coherent Demodulation of SSB
)2sin()(ˆ)2cos()()( tftmAtftmAts cccc
)4sin()(ˆ2
)4cos()(2
)(2
)2sin()2cos()(ˆ)2(cos)()( 2
tftmA
tftmA
tmA
tftftmAtftmAty
cc
ccc
ccccc
)(2
tmAc
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Effect of Phase error on SSB
)(ts
)2sin()(ˆ)2cos()()( tftmAtftmAts cccc
termsfrequencyhightmA
tmA
tftftmAtftftmAty
cc
cccccc
)sin()(ˆ2
)cos()(2
)2sin()2cos()(ˆ)2cos()2cos()()(
2 2
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Power Calculations of SSB
a
Instantaneous amplitude:
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Power Calculations of SSB
)(
)](ˆ)([2
)(2
1
22
222
2
tmA
tmtmA
tCP
c
c
avg
)(ˆ)(max2
222
tmtmA
P cPEP
])(ˆ)([)( 22 tmtmAtC c
)](ˆ)([)( 22 tmtmAtC c
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Bandwidth of SSB
The bandwidth of SSB is half the
bandwidth of DSB and
conventional AM
Bandwidth of SSB is: W
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Vestigial Side Band (VSB) VSB is a special case of SSB in which a portion of
the suppressed band is allowed to be appeared.
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Generation of Vestigial Side Band (VSB)
Product Modulator:
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Vestigial Side Band Filter
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Demodulation of Vestigial Side Band
:Coherent Demodulator
4 4
4
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Conditions on VSB Filter W
W -W
W
The constrans on VSB
Filter to undistorted recovery
of VSB signal is:
BPF
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Comparison among AM, DSB, SSB & VSB
Important !!!
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Applications: VSB
Television Signal:
The modulation format used to transmit a video signal of TV is affected by:
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Applications: VSB carrier
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Dr. Ahmed El-Mahdy COMM 601: Modulation I
Applications: VSB
a
....8
1
2
11)1( 22/1 xxxTaylor series expansion:
a
Ac=1 Add Carrier with Large Amplitude
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