MATLAB code for Constellation Diagram of QPSK

MATLAB Script

% QPSK Modulation and Demodulation

% Define input data
data = [1 1 0 1 0 1 0 0 1 0]; % Information

% Modulation
M = 4; % Number of symbols
k = log2(M); % Number of bits per symbol
bits_per_symbol = length(data) / k;
data_reshaped = reshape(data, k, bits_per_symbol)';
symbol = bi2de(data_reshaped, 'left-msb')';

% Generate QPSK modulation symbols
modulated_signal = pskmod(symbol, M, pi/4); % Phase offset pi/4 for QPSK

% AWGN Channel (Additive White Gaussian Noise)
EbNo = 10; % Energy per bit to noise power spectral density ratio (dB)
SNR = EbNo + 10*log10(k); % Signal to Noise Ratio (dB)
rx_signal = awgn(modulated_signal, SNR, 'measured');

% Demodulation
demodulated_signal = pskdemod(rx_signal, M, pi/4); % Phase offset pi/4 for QPSK

% Convert symbols to bits
demodulated_bits = de2bi(demodulated_signal, k, 'left-msb')';
received_data = reshape(demodulated_bits', 1, []);

% Plot original and received data
figure;
subplot(2,1,1);
stem(data, 'linewidth', 2);
title('Original Data');
xlabel('Bit');
ylabel('Amplitude');
axis([0 length(data) 0 1.5]);

subplot(2,1,2);
stem(received_data, 'linewidth', 2);
title('Received Data');
xlabel('Bit');
ylabel('Amplitude');
axis([0 length(received_data) 0 1.5]);

% Scatter plot
% Define demodulated symbols
demodulated_symbols = demodulated_signal; % Replace with your demodulated symbols

% Map demodulated symbols to complex constellation points
constellation_points = [1+1i, -1+1i, -1-1i, 1-1i]; % QPSK constellation points
figure()
scatter(real(constellation_points(demodulated_symbols+1)), imag(constellation_points(demodulated_symbols+1)));
title('QPSK Constellation Diagram');
xlabel('In-phase Component');
ylabel('Quadrature Component');
axis([-2 2 -2 2]); % Adjust axis limits if needed
grid on;

Output

Fig 1: QPSK Modulation and Demodulation

Fig 2: Constellation Diagram of QPSK

Copy the MATLAB Code from here

% The code is written by SalimWireless.Com % QPSK Modulation and Demodulation % Define input data data = [1 1 0 1 0 1 0 0 1 0]; % Information % Modulation M = 4; % Number of symbols k = log2(M); % Number of bits per symbol bits_per_symbol = length(data) / k; data_reshaped = reshape(data, k, bits_per_symbol)'; symbol = bi2de(data_reshaped, 'left-msb')'; % Generate QPSK modulation symbols modulated_signal = pskmod(symbol, M, pi/4); % Phase offset pi/4 for QPSK % AWGN Channel (Additive White Gaussian Noise) EbNo = 10; % Energy per bit to noise power spectral density ratio (dB) SNR = EbNo + 10*log10(k); % Signal to Noise Ratio (dB) rx_signal = awgn(modulated_signal, SNR, 'measured'); % Demodulation demodulated_signal = pskdemod(rx_signal, M, pi/4); % Phase offset pi/4 for QPSK % Convert symbols to bits demodulated_bits = de2bi(demodulated_signal, k, 'left-msb')'; received_data = reshape(demodulated_bits', 1, []); % Plot original and received data figure; subplot(2,1,1); stem(data, 'linewidth', 2); title('Original Data'); xlabel('Bit'); ylabel('Amplitude'); axis([0 length(data) 0 1.5]); subplot(2,1,2); stem(received_data, 'linewidth', 2); title('Received Data'); xlabel('Bit'); ylabel('Amplitude'); axis([0 length(received_data) 0 1.5]); % Scatter plot % Define demodulated symbols demodulated_symbols = demodulated_signal; % Replace with your demodulated symbols % Map demodulated symbols to complex constellation points constellation_points = [1+1i, -1+1i, -1-1i, 1-1i]; % QPSK constellation points figure() scatter(real(constellation_points(demodulated_symbols+1)), imag(constellation_points(demodulated_symbols+1))); title('QPSK Constellation Diagram'); xlabel('In-phase Component'); ylabel('Quadrature Component'); axis([-2 2 -2 2]); % Adjust axis limits if needed grid on;

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