AM.m

clear all;close all;clc;

carrier_amp = 1;
carrier_frq = 10;
message_amp = 1;
message_frq = 1;

Total_time = 5;
t = 0 : 0.001: Total_time;

message_signal = message_amp * sin(2 * pi * message_frq/2 * t);
carrier_signal = carrier_amp * sin(2 * pi * carrier_frq * t);

modulated_signal = (carrier_amp + message_signal) .* carrier_signal;


function m = amDemod(modulated_signal,fc,fs,n)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Function amDemod()
% Goal  : Demodulation of an AM signal
% IN    : - modulated_signal : AM modulated signal
%         - fc: Carrier signal frequency
%         - fs: Sampling frequency
%         - n : Number of carrier signal periods
% IN/OUT: -
% OUT   : - m : Original demodulated signal
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % Rectify the modulated signal
  modulated_signal = abs(modulated_signal);
  % Set the number of samples on which to do the moving average
  k = round(n*fs/fc);
  % Take the moving average
  m = movmean(modulated_signal,k);
  % Remove the DC offset
  m = m-mean(m);
end

demodulated_signal = amDemod(modulated_signal, carrier_frq, message_frq, length(t));

subplot(411);
plot(t, carrier_signal);
title('Carrier Signal');

subplot(412);
plot(t, message_signal);
title('Message Signal');
line ([0, Total_time], [0 0], "linestyle", "--", "color", "r");

subplot(413);
plot(t, modulated_signal);
title('Amplitude Modulated Signal');
line ([0, Total_time], [0 0], "linestyle", "--", "color", "r");

subplot(414);
plot(t, demodulated_signal);
title('Amplitude Demodulated Signal');
line ([0, Total_time], [0 0], "linestyle", "--", "color", "r");