%顯示模擬調制的波形及解調方法VSB
%信源
close all;
clear all;
dt = 0.001;          %時間采樣間隔         
fm=5;                %信源最高頻率
fc=20;               %載波中心頻率
T=5;                 %信號時長
t = 0:dt:T; 
mt = sqrt(2)*( cos(2*pi*fm*t)+sin(2*pi*0.5*fm*t)  );  %信源

%VSB modulation
s_vsb = mt.*cos(2*pi*fc*t);
B=1.2*fm;
[f,sf] = T2F(t,s_vsb);
[t,s_vsb] = vsbpf(f,sf,0.2*fm,1.2*fm,fc);
figure(1)
subplot(311)
plot(t,s_vsb);hold on;     %畫出VSB信號波形
plot(t,mt,'r--');          %標示mt的波形
title('VSB調制信號');
xlabel('t');

%VSB demodulation
rt = s_vsb.*cos(2*pi*fc*t);
%rt = rt-mean(rt);
[f,rf] = T2F(t,rt);
[t,rt] = lpf(f,rf,2*fm);

subplot(312)
plot(t,rt); hold on;
plot(t,mt/2,'r--');
title('相干解調后的信號波形與輸入信號的比較');
xlabel('t')
subplot(313)
[f,sf]=T2F(t,s_vsb);
psf = (abs(sf).^2)/T;
plot(f,psf);
axis([-2*fc 2*fc 0 max(psf)]);
title('VSB信號功率譜');
xlabel('f');