In a pulse-position modulation system, what parameter does the modulating signal vary?

In pulse-position modulation (PPM), the key characteristic is that the modulating signal influences the timing of the pulses. This means that instead of varying the amplitude, frequency, or width of the pulses, the position in time where each pulse occurs is adjusted according to the amplitude of the modulating signal. In other words, when the amplitude of the modulating signal is high, the pulse will be sent at an earlier position within the designated time interval, and when the amplitude is lower, the pulse will occur later.

This technique allows information to be conveyed through the specific timing of the pulses rather than their shape or size. It is crucial for applications in optical communication and other systems where timing is essential. Understanding this fundamental aspect of pulse-position modulation clarifies how it differs from other modulation techniques, which might adjust amplitude or width instead.