function [peideal,pesystem]=qpsk_berest(xx,yy,ebn0db,eb,tb,nbw)
[n1 n2]=size(xx);nx=n1*n2;
[n3 n4]=size(yy);ny=n3*n4;
[n5 n6]=size(ebn0db);neb=n5*n6;
nbwideal=1/(2*tb*2);
for m=1:neb
    peideal(m)=0.0;pesystem(m)=0.0;
    string1=['Eb/No = ',num2str(ebn0db(m))];
    disp(string1);
    ebn0(m)=10^(ebn0db(m)/10);
    n0=eb/ebn0(m);
    sigma=sqrt(n0*nbw*2);
    sigma1=sqrt(n0*nbwideal*2);
    b=sqrt(2*eb/tb)/sqrt(sum(abs(xx).^2)/nx);
    for n=1:nx
        theta=angle(xx(n));
        if (theta<0)
            theta=theta+2*pi;
        end
        xxx(n)=b*xx(n)*exp(-i*(theta-(pi/4)));
        yyy(n)=yy(n)*exp(-i*(theta-(pi/4)));
        d1=real(xxx(n));d2=imag(xxx(n));
        d3=real(yyy(n));d4=imag(yyy(n));
        pe1=q(d1/sigma1)+q(d2/sigma1);
        pe2=q(d3/sigma)+q(d4/sigma);
        peideal(m)=peideal(m)+pe1;
        pesystem(m)=pesystem(m)+pe2;
    end
end
peideal=(1/2)*peideal./nx;
pesystem=(1/2)*pesystem./nx;