Analog Communication - Practical 8

Aim

To study and perform Pulse Position Modulation and demodulation.

Theory

Pulse Position Modulation (PPM) is a modulation technique where the position of a pulse in time is varied in accordance with the message signal. The amplitude and width of the pulse remain constant, but the position of the pulse shifts based on the input signal's amplitude.

PPM is used in various communication systems where bandwidth efficiency is crucial. Demodulation involves detecting the position of the pulse and converting it back into the original message signal.

MATLAB Code

            clc;
            clear all;
            close all;
            fc=1000; %CARRIER FREQUENCY
            fs=10000; %SAMPLING FREQUENCY
            fm=200;   %MESSAGE FREQUENCY
            t=0:1/fs:((2/fm)-(1/fs));
            X= 0.4*cos(2*pi*fm*t)+0.5;%MESSAGE SIGNAL
            Y= modulate(X,fc,fs,'PPM');
            subplot(3,1,1);
            plot(X);
            title('Message Signal');
            subplot(3,1,2);
            plot(Y);
            axis([0 500 -0.2 1.2]);
            title('PPM Modulated Signal');
            xlabel('Time');
            ylabel('Amplitude');
            demoddi=demod(Y,fc,fs,'ppm');
            subplot(3,1,3);
            plot(demoddi);
            title('PPM Demod');
            xlabel('Time');
            ylabel('Amplitude');