Pulse Position Modulation

Pulse-position modulation is a form of signal modulation in which M message bits are encoded by transmitting a single pulse in one of possible time-shifts. This is repeated every T seconds, such that the transmitted bit rate is M/T bits per second. It is primarily useful for optical communications systems, where there tends to be little or no multipath interference.
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Modulation in which the temporal positions of the pulses are varied in accordance with some characteristic of the modulating signal. (188 )