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

4. 9 MATLAB Exercises 181
where
E(t) = Jm 2 (t) + m(t)
0(t) = tan- 1 [ ±m h (t) ]
m(t)
Squaring this signal yields
cp gsB (t) = E 2 (t) cos 2 !cv c t + 0(t)]
E 2 (t)
= --{l + cos [2cv c t + 20(t)]}
2
The signal E 2 (t) is eliminated by a bandpass filter. Unfortunately, the remaining signal is not a
pure sinusoid of frequency 2cv c (as was the case for DSB). There is nothing we can do to remove
the time-varying phase 20(t) from this sinusoid. Hence, for SSB, the squaring technique does
not work. The same argument can be used to show that the Costas loop will not work either.
These conclusions also apply to VSB signals.
4.9 MATLAB EXERCISES
In this section, we provide MATLAB exercises to reinforce some of the basic concepts on
analog modulations covered in earlier sections. We will cover examples that illustrate the
modulation and demodulation of DSB-SC, AM, SSB-SC, and QAM.
DSB-SC Modulation and Demodulation
The first MATLAB program, triples inc .m, is to generate a signal that is (almost) strictly
band-limited and consists of three different delayed version of the sine signal:
m2 (t) = 2 sine (2t /T a ) + sine (2t /T a + 1) + sine (2t /T a - l)
% (triplesinc .m)
% Baseband signal for AM
% Usage m=triplesinc (t,Ta)
function m=triplesinc (t,Ta)
% t is the length of the signal
% Ta is the parameter, equaling twice the delay
%
sig_l=sinc (2*t/Ta) ;
sig_2=sinc (2*t/Ta-1 );
sig_3=sinc (2*t/Ta+l );
m=2 * sig_l+sig_2+sig_3 ;
end
The DSB-SC signal can be generated with the MATLAB file ExampleDSB . m that generates
a DSB-SC signal for t= E (-0.04, 0.04). The carrier frequency is 300 Hz. The original