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1 2013 Digital televsion techniques – Lecture 5
Lecture 5
Digital television
Modulation techniques
• Electromagnetic waves
• Analog modulation
• Amplitude modulation
• Angle modulation
• Frequency modulation
• Phase modulation
• Digital modulation
• On-Off keying
• Amplitude shift keying
• Phase shift keying
• Quadrature amplitude modulation
2 2013 Digital televsion techniques – Lecture 5
Electromagnetic waves
3 2013 Digital televsion techniques – Lecture 5
Electromagnetic waves
4 2013 Digital televsion techniques – Lecture 5
Modulation
"modulate" is "To adjust or adapt to a certain proportion."
”Linear” modulation
Exponential modulation
5 2013 Digital televsion techniques – Lecture 5
Amplitude modulation
E.g..
• AM radio stations
• Analog television
6 2013 Digital televsion techniques – Lecture 5
Amplitude modulation
7 2013 Digital televsion techniques – Lecture 5
AM: waveforms and bandwidth
AM in frequency domain:
AM bandwidth is twice the message bandwidth W:
x t A x t t
A t x t t
C C m C
C C m C
( ) [ ( )]cos( )
cos( ) ( )cos( )
1
Carrier Information carrying part
X f A f f A X f fC C C C m C( ) ( ) / ( ) / 2 2
Carrier Information carrying part
f 0( )for brief notations
8 2013 Digital televsion techniques – Lecture 5
9 2013 Digital televsion techniques – Lecture 5
10 2013 Digital televsion techniques – Lecture 5
Frequency modulation (FM)
In frequency modulation carrier instantaneous frequency is