close all;
Fs=1000;
L=2;
n=0:1/Fs:L;
N=length(n);
e=randn(1,N); 
x1=sin(2*pi*40*n);
x=x1+2*e;
k=5;
m=(N-1)/k;
xk=zeros(k,m);
X=zeros(k,2*m);
Rx=zeros(k,4*m-1);
M=zeros(k,2*m);
P=zeros(k,m);
for i=1:k
    xk(i,:)=x((i-1)*m+1:i*m);
    b=kaiser(m)';
    P(i,:)=xk(i,:).*b;
    z=zeros(1,m);
    X(i,:)=[P(i,:) z];
    Rx(i,:)=xcorr(X(i,:),X(i,:));
    M(i,:)=abs(fft(Rx(i,:),2*m));
end
Sk=mean(M);
plot((1:2*m)*Fs/(2*m),Sk);