Literatura

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 ?Zdzislaw Papir
2
Definition of modulation

• Modulation involves three signals
• information carrying signal modulating signal
  x(t)
• carrier c(t)
• modulated signal f(t)

• Modulation is mapping of the information signal
  into one of the parameters of the carrier.
• The output signal is called the modulated signal.

Modulation Detection ?Zdzislaw Papir
3
Amplitude modulation
Modulation Detection ?Zdzislaw Papir
4
Amplitude Modulation
Modulation Detection ?Zdzislaw Papir
5
Baseband modulation(line code, transmission code)
Transition graph for Millers code
Modulation Detection ?Zdzislaw Papir
6
Baseband modulation(line code)
Modulation Detection ?Zdzislaw Papir
7
Spectra of informationsource 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 ?Zdzislaw Papir
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Purposes of usingmodulation
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 ?Zdzislaw Papir
9
Purposes ofusing modulation
Better noise immunity of transmission
SNR
modulation
detection
improvment of the Signal to Noise Ratio
(SNR) SNR (modulation detection) gt SNR
(baseband system) (modulation gain)
Modulation Detection ?Zdzislaw Papir
10
Purposes of usingmodulation
Frequency
Division Multiplex
Time
interleaved signal spectra
interleaved data blocks
Modulation Detection ?Zdzislaw Papir
11
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 ?m rad/s spectrum of the
  modulating signal

spectrum wideningcoefficient
Modulation Detection ?Zdzislaw Papir
12
Definition of Demodulation
Modulation is MAPPING the information signal
onto the carrier.
Demodulation is STRIPPING the information
signal from the modulated carrier.
f(t)
x(t)
DEMODULATOR
c(t)
Modulation Detection ?Zdzislaw Papir
13
Definition of Detection
Detection is STRIPPING the information signal
from the carrier in a noisy environment.
f(t) noise
x(t) noise
DETECTION
c(t)
Modulation Detection ?Zdzislaw Papir
14
The Whole Picture
Modulation Detection ?Zdzislaw Papir
15
Transmitter
LPF
MOD
BPF
Modulatedsignal
Informationsignal
Carrier
LPF Lowpass Filter BPF Bandpass Filter MOD
Modulator
Modulation Detection ?Zdzislaw Papir
16
Receiver
BPF
DEMOD
LPF
Informationsignal
Modulatedsignal
Carrier
LPF Lowpass Filter BPF Bandpass
Filter DEMOD Demodulator
Modulation Detection ?Zdzislaw Papir
17
Transmission Channel
The common assumption is that the transmission
channel disturbes the signal being transmitted
withthe Additive White Gaussian Noise.
AWGN Additive White Gaussian Noise
Modulation Detection ?Zdzislaw Papir
18
Transmission System
LPF
MOD
BPF
BPF
DEMOD
LPF
Modulation Detection ?Zdzislaw Papir
19
Transmission System Quality
LPF
MOD
BPF
BPF
DEMOD
LPF
Modulation Detection ?Zdzislaw Papir
20
Classification of Modulations
Digital - Analog
Digital - Analog

• Analog waveform sin or cos waveform (A)
• Digital waveform sequence of pulses (D)

Modulation Detection ?Zdzislaw Papir
21
Classification of Modulations
carrier
A
DSB
A
D
informationsignal
D
Modulation Detection ?Zdzislaw Papir