clear;

N = 10^6;  % Number of bits

rng(100);  % Initialize random number generator

% randn('state',200); % Deprecated, replaced by rng

% Transmitter

ip = rand(1,N) > 0.5;        % Generate random bits (0 or 1)

s = 2*ip - 1;                % BPSK modulation: 0 -> -1, 1 -> +1

% Noise

n = 1/sqrt(2) * (randn(1,N) + 1j*randn(1,N));  % AWGN with 0 dB noise variance

Eb_N0_dB = -3:10;  % Range of Eb/N0 values

nErr = zeros(1,length(Eb_N0_dB));  % To store number of errors

% Simulation loop

for ii = 1:length(Eb_N0_dB)

    % Add noise based on current Eb/N0

    y = s + 10^(-Eb_N0_dB(ii)/20) * n;

    % Receiver - Hard decision decoding

    ipHat = real(y) > 0;

    % Count errors

    nErr(ii) = sum(ip ~= ipHat);

end

% BER Calculation

simBer = nErr / N;  % Simulated BER

theoryBer = 0.5 * erfc(sqrt(10.^(Eb_N0_dB / 10)));  % Theoretical BER for BPSK

% Plotting

figure;

semilogy(Eb_N0_dB, theoryBer, 'b.-'); hold on;

semilogy(Eb_N0_dB, simBer, 'mx-');

axis([-3 10 10^-5 0.5]);

grid on;

legend('Theoretical', 'Simulated');

xlabel('Eb/N0 (dB)');

ylabel('Bit Error Rate (BER)');

title('BER Performance of BPSK over AWGN Channel');

%