# How do you plot pulse positions for a simple sine wave in MATLAB?

If you goto 14 minutes and 53 seconds of this video: https://youtu.be/xfxQ-zBp2OQ you will see a plot of Pulse Width Modulation (PWM) and Pulse Position Modulation (PPM) for a simple sine wave signal.

The picture should look something like this:

How do I implement a PPM for a sine wave in MATLAB? Here is what I am thinking:

t = 0:1/1e3:60;
d = [0:2:60;sin(2*pi*0.05*(0:2:60))]';
x = @rectpuls;
y = pulstran(t,d,x);
plot(t,y)
hold off
xlabel('Time (s)')
ylabel('Waveform')


But this gives me a plot of rectangular samples of the sine wave:

not the PPM as shown in the first graphic above.

So even though I understand what the YouTuber is doing graphically, I'm not sure how this can be implemented in MATLAB from an algorithmic standpoint.

I would appreciate any feedback from the EE community.

• What's in @rectpuls? It appears you've asked for an amplitude modulated rectangular pulse, and got one! Rewrite it to give you width modulated pulses following your own example. Or show us what's in the rectpuls function. – Neil_UK Mar 13 '20 at 7:31

It turns out this code does exactly what I want:

code sample 8 from: https://www.jcbrolabs.org/matlab-codes

% This file simulate Pulse Position Modulation (PPM) as per message signal amplitude
%
% Created By: JCBRO Labs
% Date: 03/06/2017
% website: www.jcbrolabs.org
% mail: jcbrolabs@gmail.com
clc; clear all; close all;
fc = 20;    %carrier frequency
fm = 2;     % message frequency
fs = 1000;  % sampling frequency
t = 1;
n = [0:1/fs:t];
n = n(1:end - 1);
duty = 10;
% no. of samples in one square wave period
per = fs/fc;
% no. of samples in on time
on_t = per/duty;

s = square(2*pi*fc*n,duty);
s(find(s<0)) = 0;
% message signal
m = sin(2*pi*fm*n);

% Triangular wave
A=1.25;
c=A.*sawtooth(2*pi*fc*n);%Carrier sawtooth

%
ppm = zeros(1,length(s));

% find ids where carrier is greater than message
id = find(c > m);
idd = diff(id);
iddd = find(idd ~= 1);
temp(1) = id(1);
temp(2:length(iddd)+1) = id(iddd + 1);

% ppm signal
for i = 1:length(temp)
ppm(temp(i) : temp(i) + on_t - 1) = 1;
end
% Plot
subplot(3,1,1);plot(n,m,'LineWidth',2);title('Message Signal');hold on; plot(n,c,'r','LineWidth',2);grid on;
subplot(3,1,2);plot(n,s,'LineWidth',2);title('Pulse Train');grid on; ylim([-0.2 1.2]);
subplot(3,1,3);plot(n,ppm,'LineWidth',2);title('PPM Signal'); grid on; ylim([-0.2 1.2]);


Running this code gives: