clc
clear
N=39; 
wc=0.15*pi; % 若為圓周角頻率 
window=hamming(N+1); 
b=fir1(N,wc/pi,'low',window); 
t=0:0.01:0.39;
n=length(t);
xn1=sin(10*pi*t)+10*sin(120*pi*t)+0.5*randn(1,n);
t=0.4:0.01:1.19;
n=length(t);
xn2=sin(5*pi*t)+10*sin(120*pi*t)+0.5*randn(1,n);
t=1.2:0.01:1.59;
n=length(t);
xn3=sin(10*pi*t)+10*sin(120*pi*t)+0.5*randn(1,n);
t=1.6:0.01:1.99;
n=length(t);
xn4=sin(5*pi*t)+10*sin(120*pi*t)+0.5*randn(1,n);
xn=[xn1 xn2 xn3 xn4];
x=conv(xn,b);
n=length(xn);
x=x((N+1)/2:n+(N-1)/2);
if x(1)>0
    m(1)=1;
else
    m(1)=0;
end
i=1;
k=2;l=1
while k<=n & l<=n
    if x(k)*x(l)<=0| x(k)==0
        m(k)=1-m(l);
        count(i)=l;
        k=k+1;i=i+1;l=l+1;
    else m(k)=m(l);
        k=k+1;l=l+1;
    if k==length(x);
        count(i)=n;
    end
    end
end
k=2;j=1;l=1;
while k<=length(count)&l<=length(count);
    if count(k)-count(l)>=25
        k=k+2;j=1;
    else
        if count(k)-count(l)>=15
        code(j)=1;k=k+1;l=l+1;j=j+1;
        else 
            if count(k)-count(l)>=5
            code(j)=0;k=k+2;j=j+1;l=l+2;
            else k=k+2;
            end
        end
    end
end
t=0:length(xn)-1;
subplot(321);plot(t,xn)
subplot(322);plot(t,sin(0.1*pi*t));axis([0,length(x),-2,+2]);
t=0:length(x)-1;
subplot(323);plot(t,m,'r',t,x,'b');axis([0,length(x),-2,+2]);
[h,w]=freqz(xn,1);
subplot(324);plot(w*50/pi,20*log10(abs(h)))
t=1:length(code);
subplot(325);plot(t,code,'.');axis([1,length(code),-2,+2]);