Analog Communication - Practical 6

Aim

To study and generate Pulse Amplitude Modulation (PAM) and demodulation using MATLAB software.

Theory

Pulse Amplitude Modulation (PAM) is a form of modulation where the amplitude of a series of pulse signals is varied in proportion to the amplitude of the analog message signal. It is widely used in communication systems as an intermediate step in digital modulation schemes.

Modulation: The amplitude of periodic pulses is modulated based on the instantaneous amplitude of the message signal.

Demodulation: The original message signal is recovered from the PAM signal, typically using a low-pass filter to remove high-frequency components.

MATLAB Code

% MATLAB Code for PAM Modulation and Demodulation
clc;
clf;
close all
clear all
t=0:1/6000:((10/1000)-(1/6000));
xa=sin(2*pi*100*abs(t));
Ts=32;
x=sin(2*pi*600*(Ts*t));
X=fft(xa,abs(x));
subplot(3,1,1)
plot(xa);
grid
subplot(3,1,2);
stem(X);
grid
Y=ifft(xa,X);
subplot(3,1,3)
plot(Y)
grid

Expected Output

The MATLAB code generates three plots to illustrate the process of PAM modulation and demodulation:

Message Signal: The original analog signal to be modulated.
PAM Signal: The modulated signal with pulse amplitudes proportional to the message signal.
Demodulated Signal: The recovered signal obtained using envelope detection.

These plots demonstrate how the amplitude of the pulses follows the message signal during modulation and how the original signal is retrieved during demodulation.