QPSK_Signaling.m

%Shift Keying Techniques - QPSK
clc
clear all
close all
M=4;  %Alphabet size
N=input("Enter the number of symbols:");  %number of symbols
nb=log(M)/log(2);  %number of bits/symbol

%Transmitter
%bit generation
b=randi([0 1],N*nb,1);  %Random binary bits
bs=b; bs(bs==0)=-1;  %converting logical to electrical
%DEMUX
bo=bs(1:2:end); %odd part
be=bs(2:2:end); %even part
xs=bo+1j*be;
scatterplot(xs);

SNRdB=1:1:15;
for ii=1:length(SNRdB)
    SNRii=SNRdB(ii);
    rn=awgn(xs,SNRii,'measured');
    figure; plot(real(rn),imag(rn),'b.',be,bo,'ro');legend('received','ideal');
    xlabel("Real"); ylabel("Imaginary");
    title(['QPSK constellation @ SNR=' num2str(SNRii),' dB']); axis([-2 2 -2 2]);
    
    bcato=real(rn); bcato(bcato>=0)=1; bcato(bcato<0)=0;
    bcate=imag(rn); bcate(bcate>=0)=1; bcate(bcate<0)=0;
    bcat=zeros(size(b)); bcat(1:2:end)=bcato;bcat(2:2:end)=bcate;
    
    snr=10^(SNRii./10);
    Eb_by_No=snr/2;
    Eb_by_No_dB(ii)=10*log10(Eb_by_No);
    BER_th(ii)=1/2*erfc(sqrt(Eb_by_No));
    BER(ii)=length(find(b~=bcat))/(N*nb);
    EVM=sqrt((sum((bo-real(rn)).^2+(be-imag(rn)).^2)/N)/var(bo+1j*be))*100;
    EVMdB(ii)=20*log10(EVM);
end
% semilogy(SNRdB,BER,'b--',SNRdB,BER_th,'r*'); axis([0 max(SNRdB) 10^-4 1]); grid on
figure;
semilogy(Eb_by_No_dB,BER,'b-',Eb_by_No_dB,BER_th,'r*');
axis([0 12 10^-7 1]);grid on;
xlabel('E_b/N_o (dB)'); ylabel('Bit error probability (P_e)');
xlabel("Real"); ylabel("Imaginary");
title('BER performance of QPSK');

% a=[Eb_by_No_dB; BER_th; BER];
% fileID=fopen('BER_QPSK.dat','w');
% fwrite(fileID, a, 'double');
% fclose(fileID);