clear
N = 10^5; % number of symbols
Es_N0_dB = [-3:20]; % multiple Eb/N0 values
ipHat = zeros(1,N);
for ii = 1:length(Es_N0_dB)
ip = (2*(rand(1,N)>0.5)-1) + j*(2*(rand(1,N)>0.5)-1); %
s = (1/sqrt(2))*ip; % normalization of energy to 1
n = 1/sqrt(2)*[randn(1,N) + j*randn(1,N)]; % white guassian noise, 0dB variance
y = s + 10^(-Es_N0_dB(ii)/20)*n; % additive white gaussian noise
% demodulation
y_re = real(y); % real
y_im = imag(y); % imaginary
ipHat(find(y_re < 0 & y_im < 0)) = -1 + -1*j;
ipHat(find(y_re >= 0 & y_im > 0)) = 1 + 1*j;
ipHat(find(y_re < 0 & y_im >= 0)) = -1 + 1*j;
ipHat(find(y_re >= 0 & y_im < 0)) = 1 - 1*j;
nErr(ii) = size(find([ip- ipHat]),2); % couting the number of errors
end
simSer_QPSK = nErr/N;
theorySer_QPSK = erfc(sqrt(0.5*(10.^(Es_N0_dB/10)))) - (1/4)*(erfc(sqrt(0.5*(10.^(Es_N0_dB/10))))).^2;
close all
figure
semilogy(Es_N0_dB,theorySer_QPSK,'b.-');
hold on
semilogy(Es_N0_dB,simSer_QPSK,'mx-');
axis([-3 15 10^-5 1])
grid on
legend('theory-QPSK', 'simulation-QPSK');
xlabel('Es/No, dB')
ylabel('Symbol Error Rate')
title('Symbol error probability curve for QPSK(4-QAM)')
function[pb,ps]=cm_sm32(SNRindB)
N=10000;
E=1;
SNR=10^(SNRindB/10);
sgma=sqrt(E/SNR)/2;
s00=[1 0];
s01=[0 1];
s11=[-1 0];
s10=[0 -1];
for i=1:N
temp=rand;
if (temp<0.25)
dsource1(i)=0;
dsource2(i)=0;
elseif (temp<0.5)
dsource1(i)=0;
dsource2(i)=1;
elseif (temp<0.75)
dsource1(i)=1;
dsource2(i)=0;
else
dsource1(i)=1;
dsource2(i)=1;
end;
end;
numofsymbolerror=0;
numofbiterror=0;
for i=1:N
n=sgma*randn(size(s00));
if((dsource1(i)==0)&(dsource2(i)==0))
r=s00+n;
elseif((dsource1(i)==0)&(dsource2(i)==1))
r=s01+n;
elseif((dsource1(i)==1)&(dsource2(i)==0))
r=s10+n;
else
r=s11+n;
end;
c00=dot(r,s00);
c01=dot(r,s01);
c10=dot(r,s10);
c11=dot(r,s11);
c_max=max([c00 c01 c10 c11]);
if (c00==c_max)
decis1=0;decis2=0;
elseif(c01==c_max)
decis1=0;decis2=1;
elseif(c10==c_max)
decis1=1;decis2=0;
else
decis1=1;decis2=1;
end;
symbolerror=0;
if(decis1~=dsource1(i))
numofbiterror=numofbiterror+1;
symbolerror=1;
end;
if(decis2~=dsource2(i))
numofbiterror=numofbiterror+1;
symbolerror=1;
end;
if(symbolerror==1)
numofsymbolerror=numofsymbolerror+1;
end;
end;
ps=numofsymbolerror/N;
pb=numofbiterror/(2*N);
