NN=256;
tb=0.5;
fs=16;
ebn0db=[1:2:14];
x=random_binary(NN,fs)+i*random_binary(NN,fs);
p0=input('Enter p0 > ');
p1=input('Enter p1 > ');
p2=input('Enter p2 > ');
p3=input('Enter p3 > ');
p4=input('Enter p4 > ');
delay=input('Enter tau > ');
delay3=input('Enter tau3 > ');
delay4=input('Enter tau4 > ');
delay0=0;
delay1=0;
delay2=delay;
delay5=delay3;
delay6=delay4;
gain1=sqrt(p1)*abs(randn(1,NN)+i*randn(1,NN));
gain2=sqrt(p2)*abs(randn(1,NN)+i*randn(1,NN));
gain3=sqrt(p3)*abs(randn(1,NN)+i*randn(1,NN));
gain4=sqrt(p4)*abs(randn(1,NN)+i*randn(1,NN));
for k=1:NN
    for kk=1:fs;
        index=(k-1)*fs+kk;
        ggain1(1,index)=gain1(1,k);
        ggain2(1,index)=gain2(1,k);
        ggain3(1,index)=gain3(1,k);
        ggain4(1,index)=gain4(1,k);
    end
end
y1=x;
 for k=1:delay2
     y2(1,k)=y1(1,k)*sqrt(p0);
 end
  for k=(delay2+1):(delay2+delay5)
      y2(1,k)=y1(1,k)*sqrt(p0)+...
      y1(1,k-delay1)*ggain1(1,k)+...
      y1(1,k-delay2)*ggain2(1,k);
end
  for k=(delay2+delay5+1):(delay2+delay5+delay6)
     y2(1,k)=y1(1,k)*sqrt(p0)+...
     y1(1,k-delay1)*ggain1(1,k)+...
     y1(1,k-delay1)*ggain2(1,k)+...
     y1(1,k-delay1)*ggain3(1,k);
end
for k=(delay2+delay5+delay6+1):(NN*fs)
     y2(1,k)=y1(1,k)*sqrt(p0)+...
     y1(1,k-delay1)*ggain1(1,k)+...
     y1(1,k-delay1)*ggain2(1,k)+...
     y1(1,k-delay1)*ggain3(1,k)+...
     y1(1,k-delay1)*ggain4(1,k);
end
b=-ones(1,fs);b=b/fs;a=1;
y=filter(b,a,y2);
[cor lags]=vxcorr(x,y);
cmax=max(max(abs(cor)));
nmax=find(abs(cor)==cmax);
timelag=lags(nmax);
corrmag=cmax;
theta=angle(cor(nmax));
y=y*exp(-i*theta);
hh=impz(b,a);
ts=1/16;
nbw=(fs/2)*sum(hh.^2);
index=(10*fs+8:fs:(NN-10)*fs+8);
xx=x(index);
yy=y(index-timelag+1);
[n1 n2]=size(y2);
ny2=n1*n2;
eb=tb*sum(sum(abs(y2).^2))/(ny2*2);
[peideal,pesystem]=qpsk_berest(xx,yy,ebn0db,eb,tb,nbw);
figure
semilogy(ebn0db,peideal,'b*-',ebn0db,pesystem,'r+-');
xlabel('E_b/N_0 (dB)');ylabel('Prabability of Error');grid
axis([0 14 10^(-10) 1])