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16.36 Communication Systems Engineering
Spring 2009
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View Full Document Lectures 6: Modulation
Eytan Modiano
Eytan Modiano
Slide 1
Modulation
•
Digital signals must be transmitted as analog waveforms
•
Baseband signals
–
Signals whose frequency components are concentrated around zero
•
Passband signals
–
Signals whose frequency components are centered at some frequency f
c
away from zero
•
Baseband signals can be converted to passband signals through
modulation
–
Multiplication by a sinusoid with frequency f
c
Eytan Modiano
Slide 2
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View Full Document Baseband signals
•
The simplest signaling scheme is pulse amplitude modulation (PAM)
–
With binary PAM a pulse of amplitude A is used to represent a “1” and a pulse
with amplitude A to represent a “0”
•
The simplest pulse is a rectangular pulse, but in practice other type of pulses
are used
–
For our discussion we will usually assume a rectangular pulse
•
If we let g(t) be the basic pulse shape, than with PAM we transmit g(t) to
represent a “1” and g(t) to represent a “0”
g(t)
1
⇒
S(t) = g(t)
A
0
⇒
S(t) = g(t)
Tb
Eytan Modiano
Slide 3
Mary PAM
•
Use M signal levels, A
1
…A
M
–
Each level can be used to represent Log
2
(M) bits
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This note was uploaded on 11/07/2011 for the course AERO 16.38 taught by Professor Alexandremegretski during the Spring '09 term at MIT.
 Spring '09
 AlexandreMegretski

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