ECCE4122 Principles of Analog Digital Communications Report

ECCE4122: Principles of Analog & Digital Communications Report is due within 2 weeks Experiment 3 SSB Modulation and Demodulation Pre-lab Draw a block diagram that describes an SSB modulator which utilizes a quadrature phase shifter (Hilbert Transform) Draw a block diagram that describes a coherent SSB demodulator.

Solution

N = 1024;
fs = 2048;
ts = 1/fs;
%t = (0:ts:1);
t=(0:N-1)/fs;
fc = 600; %Carrier frequency !! Limit fc<800 to avoid freqdomain aliasing
fm1 = 200;
Em1 = 1;

m = Em1*cos(2*pi*fm1*t); %Message
mh = Em1*cos((2*pi*fm1*t)-pi/2); %Hilbert transform of the message signal


sbu = m.*2.*cos(2*pi*fc*t) - mh.*2.*sin(2*pi*fc*t); %Expression for USB SSB
sbl = m.*2.*cos(2*pi*fc*t) + mh.*2.*sin(2*pi*fc*t); %Expression for LSB SSB

SBU = 2/N*abs(fft(sbu)); %Fourier Transform of USB SSB
SBL = 2/N*abs(fft(sbl)); %Fourier Transform of LSB SSB

freq = fs * (0 : N/2) / N;

close all;

figure(2)
subplot(221);
plot(10*t(1:200),sbu(1:200),\'r\');%Time Domain Plot of USB SSB
title(\'Time Domain Representation === USB\');
xlabel(\'Time\');

ylabel(\'Modulated Signal\');
subplot(222);
plot(10*t(1:200),sbl(1:200),\'b\');%Time Domain Plot of LSB SSB
title(\'Time Domain Representation === LSB\');
xlabel(\'Time\');

ylabel(\'Modulated Signal\');

subplot(223);
plot(freq,SBU(1:N/2+1))
title(\'Frequency Domain Representation\');
xlabel(\'Frequency(Hz)\');

ylabel(\'Spectral Magnitude\');
legend(\'USB\');
subplot(224)
plot(freq,SBL(1:N/2+1)); %Frequency domain plot
title(\'Frequency Domain Representation\');
xlabel(\'Frequency(Hz)\');

ylabel(\'Spectral Magnitude\');
legend(\'LSB\');

figure(4)
plot(freq,SBU(1:N/2+1),freq,SBL(1:N/2+1));
title(\'Frequency Domain Representation\');
xlabel(\'Frequency(Hz)\');

ylabel(\'Spectral Magnitude\');
legend(\'USB\',\'LSB\');