clc
clear all;
nr_of_bits = 2^10;
%Generating a QPSK signal
% Number of symbols to transfer
nr_of_symbols = nr_of_bits/2;
bit_sequence = floor(rand(1,nr_of_bits)*2)*2-1;
s = bit_sequence(1:nr_of_symbols) + j*bit_sequence(nr_of_symbols + 1:nr_of_bits);
%s=symbol sequence
b1=sign(real(s));
b2=sign(imag(s));
SNR_dB=[0:2:20];
maxerrors=2*logspace(5,3,length(SNR_dB));
SNR=10.^(SNR_dB./10);
N0=1./SNR;
frame=512;
relay_mode='AAF';
combining_type='MRC';
errors=zeros(length(SNR_dB),1);
index=zeros(length(SNR_dB),1);
for snr_ind=1:length(SNR_dB)
sprintf('current SNR is %d', SNR_dB(snr_ind))
while errors(snr_ind) < maxerrors(snr_ind)
index(snr_ind)=index(snr_ind)+1;
%defining the Channel gains
ch_h1=1/sqrt(2)*(randn(1)+j*randn(1));
ch_h2=1/sqrt(2)*(randn(1)+j*randn(1));
ch_h3=1/sqrt(2)*(randn(1)+j*randn(1));
ch_h4=1/sqrt(2)*(randn(1)+j*randn(1));
ch_h5=1/sqrt(2)*(randn(1)+j*randn(1));
%direct link
r=ch_h1.*s+sqrt(N0(snr_ind)/2)*(randn(1,frame)+j*randn(1,frame) );
direct_rx=r;
%sender to relay1
s2rl1_rx = channel(s,SNR_dB(snr_ind),ch_h2);
relay_out1 = relaysend(s,s2rl1_rx,SNR(snr_ind),ch_h2,relay_mode);
%relay1 to destn
r2d1_rx = channel(s,SNR_dB(snr_ind),ch_h3);
%sender to relay2
s2rl2_rx = channel(s,SNR_dB(snr_ind),ch_h4);
relay_out2 = relaysend(s,s2rl2_rx,SNR(snr_ind),ch_h4,relay_mode);
%relay2 to destn
r2d2_rx = channel(s,SNR_dB(snr_ind),ch_h5);
%receiver combining
final_rx=receiver_combining(direct_rx,r2d1_rx,r2d2_rx,ch_h1,ch_h2,ch_h3,ch_h4,ch_h5,combining_type,relay_mode);
b1_hat=sign(real(final_rx));
b2_hat=sign(imag(final_rx));
errors(snr_ind)=errors(snr_ind)+sum(b1 ~= b1_hat) + sum(b2 ~= b2_hat);
end
end
BER=errors./frame./index./2; % two bits per symbol
th=(1-BER).^frame;
BER_an = 1/2*(1- sqrt( SNR./(1+SNR) ) ); %analytical BER
hold on
xlabel('SNR(dB)');
ylabel('BER');
%legend('AAF MRC','ANALYTICAL');
%semilogy(SNR_dB,BER,SNR_dB,BER_an);
%semilogy(SNR_dB,BER_an);
