clear all;
clc;


SNR_dB = -5:4:30;
SNR = 10.^(SNR_dB/10);
NR = 2;
BER_MRC = 1:length(SNR_dB);
BER_EGC = BER_MRC;
BER_SC = BER_MRC;

bits = 10^5;
signal_power = 4;
random_bits = randi([0 1],1,bits);

x = random_bits
x(x == 0) = -sqrt(signal_power);
x(x == 1) = sqrt(signal_power);
% Calculate the BPSK representation of the message bits
Nr = [1 , 2]

% Compute BER for each value of SNR

%% Maximal Ratio Combiner

for i=1:2
    H = [randn(Nr(i),bits)+sqrt(-1)*randn(Nr(i),bits)];
    n = [randn(Nr(i),bits)+sqrt(-1)*randn(Nr(i),bits)];
    xkron=kron(ones(Nr(i),1),x);

    for j=1:length(SNR)
        noise_var = signal_power/SNR(j);
        sigma=sqrt(noise_var/2);
        y= H.*xkron+ sigma*n;
        y_n= sum(conj(H).*y,1)./sum(H.*conj(H),1);
        y_f= real(y_n) > 0;
        N_diff(i,j) = sum(random_bits ~= y_f);
    end
end

BER_MRC= N_diff(2,:)/bits;
%% Equal Gain Combining

for i=1:2
    H = [randn(Nr(i),bits)+sqrt(-1)*randn(Nr(i),bits)];
    n = [randn(Nr(i),bits)+sqrt(-1)*randn(Nr(i),bits)];
    xkron=kron(ones(Nr(i),1),x);

    for j=1:length(SNR)
        noise_var = signal_power/SNR(j);
        sigma=sqrt(noise_var/2);
        y= H.*xkron+ sigma*n;
        y_n= sum(exp(-1i*angle(H)).*y,1);
        y_f= real(y_n) > 0;
        N_diff(i,j) = sum(random_bits ~= y_f);
    end
end

BER_EGC= N_diff(2,:)/bits;
%% Selection Combiner


for i=1:2
    H = [randn(Nr(i),bits)+sqrt(-1)*randn(Nr(i),bits)];
    n = [randn(Nr(i),bits)+sqrt(-1)*randn(Nr(i),bits)];
    xkron=kron(ones(Nr(i),1),x);

    for j=1:length(SNR)
        noise_var = signal_power/SNR(j);
        sigma=sqrt(noise_var/2);
        y= H.*xkron+ sigma*n;
        inst_SNR = abs(H).^2;
        [max_SNR, indexes] = max(inst_SNR, [], 1);
        weights = zeros(size(H));
        for k = 1:length(indexes)
            weights(indexes(k), k) = 1;
        end

        y_n= sum(weights.*(y./H),1);

        y_f= real(y_n) > 0;
        N_diff(i,j) = sum(random_bits ~= y_f);
    end
end
BER_SC= N_diff(2,:)/bits;

% Plot BER Vs SNR_dB.
semilogy(SNR_dB,BER_MRC,'--');
hold on;
semilogy(SNR_dB,BER_EGC,'*-');
hold on;
semilogy(SNR_dB,BER_SC,'.-');
hold on;
grid on;
xlabel('SNR (dB)');
ylabel('Bit Error Rate');
legend('MRC','EGC','SC');

title('BER Vs SNR plot for SIMO with BPSK with MRC, EGC and SC under Rayleigh channel');