Analog Communication - Practical 7

Aim

To study and perform Pulse Width Modulation and demodulation.

Theory

Pulse Width Modulation (PWM) is a technique where the width of the pulses is varied in proportion to the amplitude of the input signal. In this modulation scheme, the signal is encoded by the width of the pulse rather than its amplitude. PWM is often used in power control and signal processing.

The demodulation process retrieves the original message signal by decoding the pulse width back to the amplitude. This can be achieved by filtering the PWM signal to recover the original message.

MATLAB Code

% PWM Signal
clc;
close all;
clear all;
t=0:0.0001:1;
s=sawtooth(2*pi*10*t+pi); % Carrier signal
m=0.75*sin(2*pi*1*t); % Message signal
n=length(s);
for i=1:n
    if (m(i)>=s(i))
        pwm(i)=1;
    elseif (m(i)<=s(i))
        pwm(i)=0;
    end
end

% Plotting
plot(t,pwm,'g',t,m,'r',t,s,'b');
ylabel('Amplitude');
axis([0  1 -1.5 1.5]);
xlabel('Time index');
title('PWM Wave');
grid on;