qpsk_berest.m

AWGN多径信道中的QPSK系统进行BER性能仿真

%File: qpsk_berest.m
function [peideal,pesystem]=qpsk_berest(xx,yy,enn0db,eb,tb,nbw)
%ebn0db is an array of Eb/N0 values in db(specified at the receiver input);
%tb is the bit duration and nbw is the noise BW
%xx is the reference (ideal) input ;yy is the distorted output;
%
ebn0db = [1:2:14];  %Eb/N0 vector
[n1 n2] = size(xx);
nx = n1*n2;
[n3 n4] = size(yy);
ny = n3*n4;
[n5 n6] = size(ebn0db);
neb = n5*n6;
%
%For comparision purposes,set the noise BW of the ideal rceiver(integrare
%and dump)to be equal to rs/2.
%
nbwideal = 1/(2*tb*2);
for m=1:neb
    peideal(m)=0.0;  pesystem(m)=0.0;  %initialize
   %
   %Find n0 and the variance of the noise.
   %
   string1 = ['Eb/n0 = ',num2str(ebn0db(m))];
   disp(string1);              %track execution
   ebn0(m) = 10^(ebn0db(m)/10); %dB to linear
   n0 = eb/ebn0(m);         %noise power
   sigma = sqrt(n0*nbw*2);  %variance
   sigma1 = sqrt(n0*nbwideal*2); %variance of ideal
   %
   %Multiply the input constellation/signal by a scale factor so that input
   %constellation and the constellations/signal at the input to receive
   %filter have the same ave power a=sqrt(2*eb/(2*tb)).
   %
   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
   %
   %Rotate x and y to the first quadrant and compute BER.
   %
   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));  %reference
   d3=real(yyy(n)); d4=imag(yyy(n));  %system
   pe1=q(d1/sigma1)+q(d2/sigma1);   %reference
   pe2=q(d3/sigma1)+q(d4/sigma1);   %system
   peideal(m)=peideal(m)+pe1;       %SER of reference
   pesystem(m)=pesystem(m)+pe2;       %SER of system
   end
end

peideal=(1/2)*peideal./nx       %convert to BER
pesystem=(1/2)*pesystem./nx    %convert to BER

%End of function file.