MATLAB Code for Pulse Position Modulation (PPM) and Demodulation

MATLAB Code for Pulse Position Modulation (PPM)

MATLAB Code for PPM (Simple)

clc; clear; close all;
% Parameters for the sine wave and PPM
A = 5;                 % Amplitude of the sine wave
f = 1;                 % Frequency of the sine wave in Hz
sampleRate = 0.1;      % Sampling interval (Δt)
numSamples = 50;       % Number of samples
t = (0:numSamples) * sampleRate;  % Time vector (from 0 to numSamples * Δt)

% Generate the sinusoidal signal x(t) = A * sin(2 * pi * f * t)
x_t = A * sin(2 * pi * f * t);

% Calculate the Pulse Position Modulation (PPM) positions
ppm_positions = zeros(1, numSamples+1); % Initialize an array for PPM pulse positions
ppm_pulses = zeros(1, numSamples+1);    % Initialize an array to store pulse heights (constant amplitude)
pulse_height = 1;                       % Constant pulse height (amplitude)

% Loop through each time sample and compute the pulse positions
for i = 1:numSamples+1
    % Calculate the pulse shift based on the amplitude of the sine wave at this time
    pulseShift = max(0, x_t(i));   % Only shift for positive amplitude
    ppm_positions(i) = t(i) + sampleRate * pulseShift;  % Pulse position calculation
    ppm_pulses(i) = pulse_height;  % Set the pulse height to constant value
end

% Plotting the sine wave and PPM
figure;

% Plot the sine wave
subplot(2,1,1);
plot(t, x_t, 'b', 'LineWidth', 2);
title('Sinusoidal Signal x(t) = 5 sin(2\pi \cdot 1 \cdot t)');
xlabel('Time (s)');
ylabel('Amplitude');
grid on;

% Plot the PPM pulses with constant height
subplot(2,1,2);
hold on;
for i = 1:numSamples+1
    if ppm_pulses(i) > 0  % Only plot pulses if there is a shift (i.e., positive amplitude)
        plot([ppm_positions(i) ppm_positions(i)], [0 ppm_pulses(i)], 'r', 'LineWidth', 2); % Vertical line for pulse
    end
end
title('Pulse Position Modulation (PPM)');
xlabel('Time (s)');
ylabel('Pulse Amplitude');
grid on;
web('https://www.salimwireless.com/search?q=ppm%20pulse%20modulation', '-browser');
    

Output

Figure: PPM Output in MATLAB

MATLAB Code for PPM (at Falling Edges of PWM)

% The code is developed by SalimWireless.com
clc; clear; close all;
% === Existing PWM generation code === (unchanged)
fs_carrier = 10;       % Carrier frequency in Hz
f_signal = 3;          % Message signal frequency in Hz
sampleRate = 50000;    % Samples per second
duration = 1;          % Duration in seconds

t = linspace(0, duration, sampleRate * duration);
signal = sin(2 * pi * f_signal * t);
normalizedSignal = (signal + 1) / 2;

samplesPerCarrierPeriod = floor(sampleRate / fs_carrier);
pwm = zeros(1, length(t));

for i = 1:samplesPerCarrierPeriod:length(t)
    startIndex = i;
    if startIndex > length(t)
        break;
    end
    duty = normalizedSignal(startIndex);
    onSamples = floor(samplesPerCarrierPeriod * duty);
    endIndex = min(startIndex + samplesPerCarrierPeriod - 1, length(t));
    onEndIndex = min(startIndex + onSamples - 1, endIndex);
    pwm(startIndex:onEndIndex) = 1;
end

carrierSquare = double(mod(t * fs_carrier, 1) < 0.5);

samplesToPlot = floor(3 * (sampleRate / f_signal));
t_plot = t(1:samplesToPlot);
signal_plot = signal(1:samplesToPlot);
carrier_plot = carrierSquare(1:samplesToPlot);
pwm_plot = pwm(1:samplesToPlot);

% === Identify falling edges of PWM ===
fallingEdges = find(diff(pwm_plot) == -1) + 1;  % indices where pwm goes 1->0

% === Generate PPM pulses at falling edges ===
ppmPulseWidth = round(sampleRate * 0.0001); % 0.1 ms pulse width for example

ppmSignal = zeros(size(pwm_plot));
for idx = fallingEdges
    pulseEnd = min(idx + ppmPulseWidth - 1, length(ppmSignal));
    ppmSignal(idx:pulseEnd) = 1;
end

% === Plot all signals ===
figure('Name', 'PWM and PPM Pulses', 'Color', 'w');
hold on;
plot(t_plot, signal_plot, 'b', 'LineWidth', 1.2);
plot(t_plot, carrier_plot, 'g--', 'LineWidth', 1);
stairs(t_plot, pwm_plot, 'r', 'LineWidth', 1.2);
stairs(t_plot, ppmSignal * 1.2, 'k', 'LineWidth', 1.5); % multiplied by 1.2 for vertical offset

hold off;
xlabel('Time (s)');
ylabel('Amplitude');
title('PWM Output with PPM Pulses at Falling Edges');
legend('Message Signal (Sine)', 'Square Carrier', 'PWM Output', 'PPM Pulses (at falling edges)', 'Location', 'southoutside', 'Orientation', 'horizontal');
grid on;
ylim([-0.2 1.5]);  % Adjust y-axis for visibility
web('https://www.salimwireless.com/search?q=pwm%20pulse%20modulation', '-browser');
    

Output

Figure: PWM and PPM Output in MATLAB

Further Reading

1. Pulse Position Modulation (Theory)
2. MATLAB Code for Pulse Amplitude Modulation (PAM) and Demodulation
3. MATLAB Code for Pulse Width Modulation (PWM) and Demodulation
4. MATLAB Code for Delta Modulation (DM) and Demodulation
5. MATLAB Code for Pulse Code Modulation (PCM) and Demodulation