clear all
global dt t f df N T %全局變量
close all 
N=2^20; 
dt=0.001; %ms 
df=1/(N*dt); %KHz 
T=N*dt; %截短時(shí)間 
Bs=N*df/2; %系統(tǒng)帶寬 
t=linspace(-T/2,T/2,N); %時(shí)域橫坐標(biāo) 
f=linspace(-Bs,Bs,N)+eps; %頻域橫坐標(biāo) 
fm=1; %模擬基帶信號(hào)頻率為1kHz 
fc=6; %正弦載波信號(hào)頻率為6kHz 
mt=cos(2*pi*fm*t); %模擬基帶信號(hào) 
m(mt>0)=1;  %發(fā)送比特
m(mt<0)=0;
c=cos(2*pi*fc*t); %正弦載波信號(hào) 
s=m.*c; %DSB-SC AM已調(diào)信號(hào) 
S=T2F(s); 
n=awgn(s,20); %AWGN信道噪聲
r=s+n; %接受信號(hào) 
y=r.*c; 
Lpfil=LPF(fc); %低通濾波器 
Y=T2F(y); 
yrt=real(F2T(Lpfil.*Y)); 
yr=yrt-mean(yrt);
yr(yr>0)=1;  %發(fā)送比特
yr(yr<0)=0;
subplot(3,1,1) 
plot(t,m,'LineWidth',1.2)
title('輸入信號(hào)');
axis([-1,+1,-0.2,1.2*max(m)]) 
xlabel('t (ms)')
ylabel('s(t) (V)') 
subplot(3,1,2) 
plot(t,s,'LineWidth',1.2) 
title('2ASK調(diào)制后波形');
axis([-1,+1,1.2*min(c),1.2*max(c)]) 
xlabel('t (ms)')
ylabel('s(t) (V)') 
subplot(3,1,3)
plot(t,yr,'LineWidth',1.2) 
axis([-1,+1,-0.2,1.2*max(yr)])
title(['2ASK解調(diào)后波形']) 
xlabel('t (ms)') 
ylabel('s(t) (V)')