86
Practical MATLAB
® Applications for Engineers
Example 1.18
An analog communication system consists of an information signal or message given
by m(t) = 3 cos(5t), and a high-frequency carrier given by f c (t) = cos(50t).
1. Create the script fi le modulation that returns the following plots:
a. m(t) versus t
b. f c (t) versus t
c. Amplitude modulated (AM) signal versus t
d. Angle modulated (FM/PM) signal versus t
2. Let us assume now that the message signal m(t) is a binary-periodic signal with
period T = 2, defi ned as follows:
m t
t
t
( ) ϭ
Ͻ Յ
Ͻ Յ
3 0
1
1 1
2



 
Obtain the plots of the following communication signals:
a. ASK versus t
b. FSK versus t
c. PSK versus t
f(n) versus n
5
−5
0
0
Amplitude
Amplitude
Amplitude
10
20
30
40
50
60
70
80
90
100
5
−5
0
f(n) is resampled with L=3/M=2
f(n) is resampled with L=2/M=3
0
50
100
150
time index n
time index n
5
0
0
1 0
2 0
3 0
4 0
5 0
6 0
time index n
−5
FIGURE 1.72
Plots of f(t) and resampled f(t) with notes given by L/M of Example 1.17.
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7/25/2008 4:16:28 PM