% symbol error rate for QPSK(4-QAM) modulation
clear
N = 1000; % number of symbols
run=100;
snr = -20:5:20; % multiple Eb/N0 values
dataHat = zeros(1,N);
for ii = 1:length(snr)
for run=1:100
data = (2*(rand(1,N)>0.5)-1) + j*(2*(rand(1,N)>0.5)-1); %
s = (1/sqrt(2))*data; % normalization of energy to 1
n = 1/sqrt(2)*[randn(1,N) + j*randn(1,N)]; % white guassian noise, 0dB variance
y = s + 10^(-snr(ii)/20)*n; % additive white gaussian noise
% demodulation
y_re = real(y); % real
y_im = imag(y); % imaginary
dataHat(find(y_re < 0 & y_im < 0)) = -1 + -1*j;
dataHat(find(y_re >= 0 & y_im > 0)) = 1 + 1*j;
dataHat(find(y_re < 0 & y_im >= 0)) = -1 + 1*j;
dataHat(find(y_re >= 0 & y_im < 0)) = 1 - 1*j;
T_Error(ii) = size(find([data - dataHat]),2); % couting the number of errors
end
end
simSer_QPSK = T_Error/N;
theorySer_QPSK = erfc(sqrt(0.5*(10.^(snr/10)))) - (1/4)*(erfc(sqrt(0.5*(10.^(snr/10))))).^2;
close all
figure
semilogy(snr,theorySer_QPSK,'b.-');
hold on
semilogy(snr,simSer_QPSK,'mx-');
grid on
legend('theory-QPSK', 'simulation-QPSK');
xlabel('Es/No, dB')
ylabel('Symbol Error Rate')
title('Symbol error probability curve for QPSK(4-QAM)')
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