lecture 7-8 dsb-sc am mod i - at
TRANSCRIPT
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Communication Systems-
Communication Systems
Instructor: Dr. Muhammad Arif
The University of Lahore –Islamaad !ampus
Lecture 7-8Date 14 March 2016
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Overview
Chapter 4.1-4.2, Basics of amplitude modulation Baseband vs Carrier Modulation
Why Modulation
Double Side Band Carrier Suppressed Modulation (BSD-SC)
Types o Modulators
– Multiplier Modulator
– !inear Modulator
– Switchin" Modulator
– #in" Modulator
$re%uency Convertor
Demodulation o DSB-SC Si"nals
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Baseband and Carrier
Communication Baseband&
− Describes si"nals and systems whose ran"e o re%uencies is measuredrom ' to a maimum bandwidth or hi"hest si"nal re%uency
− oice& Telephone '-*+,./0 CD '-11+',./
− ideo& 2nalo" T 3+,M./4 T channel is '-5M./+ Di"ital4 dependin"on the si/e4 movement4 rames per second4 6
− 7ample& wire4 coaial cable4 optical iber4 8CM phone
Carrier Communication&− Carrier& a waveorm (usually sinusoidal) that is modulated to
represent the inormation to be transmitted+ This carrier wave is usuallyo much hi"her re%uency than the modulatin" (baseband) si"nal+
− Modulation& is the process o varyin" a carrier signal in order to usethat si"nal to convey inormation+
http://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/Sinusoidalhttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Transmission_(telecommunications)http://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/Informationhttp://en.wikipedia.org/wiki/Informationhttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Transmission_(telecommunications)http://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Sinusoidalhttp://en.wikipedia.org/wiki/Waveform
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Communication-
Modulation
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Modulation Modulation
− 2 process that causes a shit in the ran"e o re%uencies o a si"nal+ 9ain advanta"es
− 2ntenna si/e& hal o the antenna si/e+ Thousands o miles or baseband
− Better usa"e o limited bandwidth& less side lopes
− Trade bandwidth or S:#& CDM2
− #obust to inter-symbol-intererence (multipath delay)
− #obust to errors and distortions
Types−
2nalo"& 2M (DSB4 SSB4 SB)4 $M4 Delta modulation− Di"ital& 2S4 $S4 8S4 ;2M4 6
− 8ulse modulation& 8CM4 8DM4 6 $iber4 phone
2dvanced& CDM2 (*9)4 O$DM (W!2:4 WM2:)4 6+
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#
2M-DSB-SC
7ample 3+<
0
0
Upper sideband (USB)Lower sideband (LSB)
0
→t
→t
→t
)( t m
)t(
ϕ
↑
)( ω M
→ω
)( ω Φ
→ωcωcω−
)t(ϕ
)tcos( cω
)= t c$% ω cos(
cω
π
→ω
)( t m)cos( ct ω
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