PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

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 fc(t) = cos(50t).

1. Create the script fi le modulation that returns the following plots:
   a. m(t) versus t
   b. fc(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:

mt

t

t

()

   

   

30 1

11 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

010 2030405060

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.