B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

182 AMPLITUDE MODULATIONS AND DEMODULATIONS
Figure 4.31
Example signals
in time and
frequency
domains during
DSB-SC
modulation.
2 200
1 50
Q
'g' 0 100
-1 50
11
Q
-2
-0.03 -0.02 -0.01 0 0.01 0.02 0.03
0
-600 -400 -200 0 200 400 600
t(sec)
f(Hz)
"' 0
Ci "'
2 200
150
"'
i3 JOO
-1 50
-2
-0.03 -0.02 -0.01 0 0.01 0.02 0.03 -400 -200 0 200 400 600
t(sec)
f(Hz)
.,,s
message signal and the DSB-SC signal for both time and frequency domains are illustrated in
Fig. 4.31.
% (ExarnpleDSB .m)
% This program uses triplesinc .m to illustrate DSB modulation
% and demodulation
ts=l .e-4
t=-0 .04:ts:0.04;
Ta=0 .01;
m_s ig=triplesinc (t,Ta) ;
Lfft=length (t) ; Lfft=2 A ceil ( log2 (Lfft) );
M_fre=fftshift ( fft (m_sig,Lfft) );
freqm= (-Lfft/2:L fft/2-1)/(Lfft*ts) ;
s_dsb=m_sig.*cos (2*pi*500*t) ;
Lfft=length (t) ; Lfft=2 A ceil ( log2 (Lfft)+l) ;
S_dsb=fftshift (fft (s_dsb, Lfft) );
freqs= (-Lfft/2 :Lfft/2-1)/(Lfft*ts) ;
Trange= [ -0 .03 0.03 -2 2]
figure (l)
subplot (22l) ; tdl=plot (t,m_sig) ;
axis ( Trange ) ; set (tdl , 'Linewidth' , 2) ;