PULSE POSITION MODULATION (PPM) - Basics, Definition and Waveform of PPM

Pulse modulation can be categorized broadly into two types-
#Analog modulation and
#Digital modulation
The analog pulse modulation can again be of two types-

Pulse Position Modulation Video [HD]

 

#Pulse Amplitude Modulation (PAM)
#Pulse Time Modulation (PTM)
The Pulse Time Modulation (PTM) can further be classified into two types of modulation-
#Pulse Width Modulation (PWM)/Pulse Duration Modulation (PDM)
#Pulse Position Modulation (PPM)
Pulse Code Modulation (PCM) is a digital pulse modulation technique.


You can see the classification of different types of modulation, in the image given below, (Click the image to enlarge it)-

Types of Modulation Techniques

Pulse Position Modulation (PPM)

Definition:-

In Pulse position modulation, the position of the pulsed carrier wave is varied according to the message signal (modulating signal).

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#PULSE CODE MODULATION (PCM) [ADVANTAGES AND DISADVANTAGES]
#SAMPLING THEOREM AND RECONSTRUCTION (SAMPLING AND QUANTIZATION)

Look at the waveforms shown in the image given below, (Click the image to enlarge)-

Pulse Position Modulation (PPM) Waveform

This image shows, the waveforms of modulating signal, pulsed carrier wave, pulse width modulated wave (PWM) and pulse position modulated wave (PPM).
Please note that, here we will obtain the pulse position modulated wave from the pulse width modulated wave. Therefore to draw the waveform of PPM we need to draw the waveform of PWM too.
Observe the waveforms shown in the image.
Now we know how to obtain the waveform of pulse width modulated wave. So we will get the waveform of pulse position modulation from PWM. 
As you can see in the image, that the starting point of each pulse in PPM waveform is obtained from the trailing edge of the PWM pulse. It means, each pulse in PPM starts where the PWM pulse ends (trailing edge of PWM pulse).

Important Observations about Pulse Position Modulation (PPM)

#It is important to note that in pulse position modulation, only the position of of the pulses changes as per the variations in amplitude of the modulating signal. 
#There is no change in the amplitude or width of the pulses of the carrier wave. So the information about the modulating signal is present in the position variations of the pulses. 
#In pulse position modulation, synchronizing pulses need to be sent by the transmitter to keep the transmitter and receiver in synchronism. This kind of synchronization is not required in case of pulse amplitude modulation or in Pulse width modulation.

Properties of Pulse Position Modulation

#Noise in PPM

Because of constant amplitude in PPM, noise interference is very less and also noise can easily be separated from the signal.

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COMPARISON OF PAM, PWM, PPM MODULATION TECHNIQUES

#Power in PPM

As in case of PPM, the amplitude and width of each pulse is same. 
Therefore transmission power for each pulse is same.

#Synchronization between transmitter and receiver in PPM

In Pulse position modulation, synchronization between transmitter and receiver is required.

#Similarity of PPM with Phase Modulation (PM)

Phase change is nothing but simply shifting of signal position on the time axis. Like phase modulation, in pulse position modulation too, the position of the pulse is varied on the time axis according to the modulating signal.

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Need and benefits of modulation
Pulse modulation techniques (PAM, PWM, PPM, PCM)
Comparison of PAM, PWM, PPM modulation techniques
Pulse amplitude modulation (PAM)
Pulse width modulation (PWM)
Pulse position modulation (PPM) 
Pulse code modulation (PCM) advantages and disadvantages
Pulse code modulation (PCM) vs differential pulse code modulation (DPCM)
Sampling theorem and reconstruction (sampling and quantization)