RF Simulation Demo: Pulse Position Modulation

[ExamplePrograms]

Theory

Pulse Position Modulation may be used to transmit analog information, such as continuous speech or data. It is a system in which continuous waveforms are sampled at regular intervals. Information regarding the signal is transmitted only at the sampling times, together with any synchronizing pulses that may be required. At the receiving end, the original waveforms may be reconstituted from the information regarding the samples, if these are taken frequently enough. Despite the fact that information about the signal is not supplied continuously as in AM and FM, the resulting receiver output can have negligible distortion.

The amplitude and width of the pulses is kept constant in this system, while the position of each pulse, in relation to the position of a recurrent reference pulse is varied by each instantaneous sampled value of the modulating wave. This means that the transmitter must send synchronizing pulses to operate timing circuits in the receiver. The pulse position modulation has the advantage of requiring constant transmitter power output, but the disadvantage of depending on transmitter-receiver synchronization.

The advantages of Pulse Position Modulation are:

• The amplitude is held constant thus less noise interference
• Signal and noise separation is very easy
• Due to constant pulse widths and amplitudes, transmission power for each pulse is same

Demonstration

1) Place the Simulate Signal VI in the block diagram and configure it

2) Place the Square Waveform VI in the block diagram in order to generate a square wave signal

3) Wire the output of the Simulate Signal VI to phase of the Square Waveform VI in order to get PWM output waveform

4) Place the Basic Level Trigger Detection VI in the block diagram to get demodulated signal waveform by specifying the parameter of mode as index and slope as Rising edge

5) Place the waveform graphs in the front panel and wire the blocks to the each output function in the block diagram

6) Place the sub diagrams in side the loop in order to repeat the operation until the stop button is enabled