function [rx1,ix1,rx2,ix2]=addnoise(x1,x2,snr,s1,s2,s3,s4)% =================================================================% function [rx1,ix1,rx2,ix2]=addnoise(x1,x2,snr,s1,s2,s3,s4)%% Generates noise sequences and adds them to the output sequences%% x1  :  1st output sequence% x2  :  2nd output sequence% snr :  the signal-to-noise-ratio% s1  :  seed for randn  (also: s2,s3,s4)%% rx1 :  real part of noisy output sequence x1% rx2 :  real part of noisy output sequence x2 % ix1 :  imaginary part of noisy output sequence x1% ix1 :  imaginary part of noisy output sequence x2%% REMARKS:% If snr<0, no noise is added --- NOISE-FREE case% If only 4 input arguments are supplied, then the output sequence% is assumed real-valued, and real-valued noise is added.%% Author: H. Pozidis,   September 23, 1998% =================================================================if (nargin == 7) if (snr >= 0)  rx1=real(x1); ix1=imag(x1); rx2=real(x2); ix2=imag(x2);  randn('seed',s1);  nr1=randn(size(rx1));    randn('seed',s2);  ni1=randn(size(ix1));  randn('seed',s3);  nr2=randn(size(rx2));    randn('seed',s4);  ni2=randn(size(ix2));  nr1=nr1-mean(nr1); ni1=ni1-mean(ni1);  nr2=nr2-mean(nr2); ni2=ni2-mean(ni2);  ss1=sum(abs(x1).^2);  ss2=sum(abs(x2).^2);  sw1=ss1/(10^(snr/10));sw2=ss2/(10^(snr/10));  sr1=sum(nr1.^2);      si1=sum(ni1.^2);  sr2=sum(nr2.^2);      si2=sum(ni2.^2);  nr1=nr1./(sr1^0.5);   ni1=ni1./(si1^0.5);  nr2=nr2./(sr2^0.5);   ni2=ni2./(si2^0.5);  nr1=nr1*((sw1/2)^0.5); ni1=ni1*((sw1/2)^0.5);  nr2=nr2*((sw2/2)^0.5); ni2=ni2*((sw2/2)^0.5);  rx1=rx1+nr1;    ix1=ix1+ni1;  rx2=rx2+nr2;    ix2=ix2+ni2;  clear nr1 ni1 nr2 ni2 ss1 ss2 sw1 sw2 sr1 sr2 si1 si2; else  rx1=real(x1);  ix1=imag(x1);  rx2=real(x2);  ix2=imag(x2); endelseif (nargin == 4)  t1=x2; t2=snr; t3=s1;  snr=t1; s1=t2; s2=t3;  if (snr >= 0)    rx1=real(x1); ix1=imag(x1);     randn('seed',s1);  nr1=randn(size(rx1));    randn('seed',s2);  ni1=randn(size(ix1));    nr1=nr1-mean(nr1); ni1=ni1-mean(ni1);       ss1=sum(abs(x1).^2);  sw1=ss1/(10^(snr/10));	    sr1=sum(nr1.^2);      si1=sum(ni1.^2);    nr1=nr1./(sr1^0.5);   ni1=ni1./(si1^0.5);	     nr1=nr1*((sw1/2)^0.5); ni1=ni1*((sw1/2)^0.5);	      rx1=rx1+nr1;    ix1=ix1+ni1;    clear nr1 ni1 ss1 sw1 sr1 si1;  else	rx1=real(x1);  ix1=imag(x1);  endelse  error('The routine ''addnoise.m'' takes 4 or 7 arguments');end