Basic Concepts „Modulation & Detection” Zdzisław Pa • Definition of modulation • Spectra of information source signals • Purposes of using modulation • Does the free lunch exist? • Definition of demodulation • Definition of detection • The whole picture – transmission system • Classification of modulations
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Basic Concepts „Modulation & Detection” Zdzisław Papir Definition of modulation Spectra of information source signals Purposes of using modulation Does.
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Basic Concepts
„Modulation & Detection” Zdzisław Papir
• Definition of modulation• Spectra of information source signals• Purposes of using modulation• Does the free lunch exist?• Definition of demodulation• Definition of detection• The whole picture – transmission system• Classification of modulations
Definition of modulation
„Modulation & Detection” Zdzisław Papir
Modulation involves three signals:• information carrying signal = modulating signal x(t)• carrier c(t)• modulated signal φ(t)
• Modulation is mapping of the information signal into one of the parameters of the carrier.• The output signal is called the modulated signal.
MODULATORφ(t)x(t)
c(t)
Amplitude modulation
„Modulation & Detection” Zdzisław Papir
ttxt
ftAtc
0
0000
cos
2,cos
MODULATOR
tAtc 00 cos
ttxt 0cos tx
Amplitude Modulation
„Modulation & Detection” Zdzisław Papir
ttxt 0cos
t
Baseband modulation(line code, transmission code)
„Modulation & Detection” Zdzisław Papir
+
–
p
p1
p
pp1
Transition graph for Miller’s code
0Pr1,1Pr pp
Baseband modulation(line code)
„Modulation & Detection” Zdzisław Papir
+
–
p
p1
p
pp1 0Pr1
1Pr
p
p
1 0 001 1 00 00 1 1 1
Spectra of informationsource signals
„Modulation & Detection” Zdzisław Papir
Voice - baseband – up to several kHzs
Sound - baseband – up to tens of kHzs
Video – baseband up to several MHzs
Raw data – baseband up to ...?
Purposes of usingmodulation
„Modulation & Detection” Zdzisław Papir
Access to different parts of the electromagnetic spectrum
Microwave - MHzs
Copper plant – baseband up to 10 MHz
Fiber – narrow frequency window at THzs
Satellite - GHzs
„Modulation & Detection” Zdzisław Papir
Better noise immunity of transmission
TRANSMITTER RECEIVERTRANSMISSIONCHANNEL
noise
modulation detectionimprovment of the Signal to Noise Ratio (SNR)