carrier_modulation.m

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% In ampliture-modulated PAM system, the transmitter filter with impulse
% response has a square-root raised-cosine spectral, with a roll-off 0.5.
%Carrier frequency is fc=40/T. 

echo off
T=1;
delta_T=T/200;
alpha=0.5;
fc=40/T;
A_m=1;
t=-5*T+delta_T:delta_T:5*T;
N=length(t);
for i=1:N
    if (abs(t(i))~=T/(2*alpha))
        g_T(i)=sinc(t(i)/T)*(cos(pi*alpha*t(i)/T)/(1-4*alpha^2*t(i)^2/T^2));
    else
        g_T(i)=0;
    end
    echo off;
end;

echo off;
G_T=abs(fft(g_T));
u_m=A_m*g_T.*cos(2*pi*fc*t);
U_m=abs(fft(u_m));

f=-0.5/delta_T:1/(delta_T*(N-1)):0.5/delta_T;

figure(1);
plot(f,fftshift(G_T),'linewidth',2);
axis([-1/T 1/T 0 max(G_T)]);

figure (2);
plot(f,fftshift(U_m),'r','linewidth',2);
axis([-50 50 0 110]);