clc; clear; close all;

N = 10;                 % Number of bits
data = randi([0 1],1,N);% Random bits
sym  = 2*data-1;        % BPSK mapping (0->-1, 1->+1)

% BPSK waveform
bit_rate = 1000; Tb = 1/bit_rate; 
t = 0:Tb/100:Tb; 
Tx = kron(sym,cos(2*pi*bit_rate*t)); 

% Add noise
SNR = 20; 
P = mean(abs(Tx).^2); 
noise = sqrt(P/10^(SNR/10))*randn(size(Tx));
Rx = Tx + noise;

% ----- Plots -----
subplot(3,1,1); plot(kron(data,ones(1,length(t))),'LineWidth',1.5);
ylim([-0.5 1.5]); grid on; title('Message Signal');

subplot(3,1,2); plot(Rx); ylim([-2 2]); grid on; title('BPSK Waveform with Noise');

subplot(3,1,3); plot(sym,zeros(1,N),'o'); xlim([-2 2]); ylim([-2 2]);
grid on; xlabel('In-Phase'); ylabel('Quadrature'); title('BPSK Constellation');