1. Basic Concepts 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
„Modulation & Detection” Zdzisław Papir

2. Definition of modulation
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.
MODULATOR
φ(t)
x(t)
c(t)
„Modulation & Detection” Zdzisław Papir

3. Amplitude modulation MODULATOR
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4. Amplitude Modulation t
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5. Baseband modulation (line code, transmission code)+ –
Transition graph for Miller’s code
„Modulation & Detection” Zdzisław Papir

6. Baseband modulation (line code) +– 1
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7. Spectra of information source signals
Voice - baseband – up to several kHzs
Sound - baseband – up to tens of kHzs
Video – baseband up to several MHzs
Raw data – baseband up to ...?
„Modulation & Detection” Zdzisław Papir

8. Access to different parts of the electromagnetic spectrum
Purposes of using modulation
Access to different parts of the electromagnetic spectrum
Microwave - MHzs
Satellite - GHzs
Copper plant – baseband up to 10 MHz
Fiber – narrow frequency window at THzs
„Modulation & Detection” Zdzisław Papir

9. Purposes of using modulation
Better noise immunity of transmission
TRANSMITTER
RECEIVER
TRANSMISSION CHANNEL
noise
SNR
modulation
detection
improvment of the Signal to Noise Ratio (SNR)
SNR (modulation & detection) > SNR (baseband system)
(modulation gain)
„Modulation & Detection” Zdzisław Papir

10. interleaved signal spectra interleaved data blocks
Purposes of using modulation
Frequency
Division Multiplex
Time
interleaved signal spectra
Frequency (FDM)
Time (TDM)
interleaved data blocks
„Modulation & Detection” Zdzisław Papir

11. spectrum widening coefficient
The free lunch does not exist
#1 Access to different parts of the electromagnetic spectrum
#2 Better noise immunity of transmission
#3 Frequency or Time Division Multiplex of transmission channels
#4 SPECTRUM WIDENING
B [Hz] or W [rad/s] – spectrum of the modulated signal
fm [Hz] or ωm [rad/s] – spectrum of the modulating signal
spectrum widening coefficient
„Modulation & Detection” Zdzisław Papir

12. Definition of Demodulation
Modulation is MAPPING the information signal onto the carrier.
MODULATOR
φ(t)
x(t)
c(t)
Demodulation is STRIPPING the information signal from the modulated carrier.
φ(t)
x(t)
DEMODULATOR
c(t)
„Modulation & Detection” Zdzisław Papir

13. Definition of Detection
Detection is STRIPPING the information signal from the carrier in a noisy environment.
φ(t) + noise
x(t) + noise
DETECTION
c(t)
„Modulation & Detection” Zdzisław Papir

14. The Whole Picture TRANSMITTER RECEIVER noise modulation detection
TRANSMISSION CHANNEL
noise
modulation
detection
„Modulation & Detection” Zdzisław Papir

15. Transmitter LPF MOD BPF Carrier LPF – Lowpass Filter
Modulated signal
Information signal
Carrier
LPF – Lowpass Filter
BPF – Bandpass Filter
MOD – Modulator
„Modulation & Detection” Zdzisław Papir

16. Receiver BPF DEMOD LPF Carrier LPF – Lowpass Filter
Modulated signal
Information signal
Carrier
LPF – Lowpass Filter
BPF – Bandpass Filter
DEMOD – Demodulator
„Modulation & Detection” Zdzisław Papir

17. Transmission Channel AWGN – Additive White Gaussian Noise
The common assumption is that
the transmission channel disturbes
the signal being transmitted with the Additive White Gaussian Noise.
AWGN – Additive White Gaussian Noise
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18. Transmission System LPF MOD BPF BPF DEMOD LPF
„Modulation & Detection” Zdzisław Papir

19. Transmission System Quality
LPF
MOD
BPF
BPF
DEMOD
LPF
„Modulation & Detection” Zdzisław Papir

20. Classification of Modulations
MODULATOR
φ(t)
x(t)
c(t)
Digital - Analog
Digital - Analog
Analog waveform – sin or cos waveform (A)
Digital waveform – sequence of pulses (D)
„Modulation & Detection” Zdzisław Papir

21. Classification of Modulations
carrier A
Keying
ASK
PSK
FSK
MSK
GMSK AM FM
SSB
QAM
Classics
DSB A D
Line codes
NRZ
Miller
HDB
PRS
Sampling theorem
PAM
PFM
PDM
information signal D
„Modulation & Detection” Zdzisław Papir