Editing Pulse-position modulation (section)

==History==
An ancient use of pulse-position modulation was the [[Hydraulic telegraph#Greek hydraulic semaphore system|Greek hydraulic semaphore system]] invented by Aeneas Stymphalus around 350 B.C. that used the [[water clock]] principle to time signals.<ref>{{cite web|author=Michael Lahanas|title=Ancient Greek Communication Methods|url=http://www.mlahanas.de/Greeks/Communication.htm|url-status=dead|archive-url=https://web.archive.org/web/20141102224501/http://www.mlahanas.de/Greeks/Communication.htm|archive-date=2014-11-02}}</ref> In this system, the draining of water acts as the timing device, and torches are used to signal the pulses. The system used identical water-filled containers whose drain could be turned on and off, and a float with a rod marked with various predetermined codes that represented military messages. The operators would place the containers on hills so they could be seen from each other at a distance. To send a message, the operators would use torches to signal the beginning and ending of the draining of the water, and the marking on the rod attached to the float would indicate the message.

In modern times, pulse-position modulation has origins in [[Telegraphy|telegraph]] [[time-division multiplexing]], which dates back to 1853, and evolved alongside [[pulse-code modulation]] and [[pulse-width modulation]].<ref>{{cite web|author=Ross Yeager & Kyle Pace|title=Copy of Communications Topic Presentation: Pulse Code Modulation|url=http://prezi.com/_qq7v08r4qxi/copy-of-communications-topic-presentation-pulse-code-modulation/|publisher=[[Prezi]]}}</ref> In the early 1960s, Don Mathers and Doug Spreng of [[NASA]] invented pulse-position modulation used in [[radio-control]] (R/C) systems. PPM is currently being used in [[fiber-optic communication]]s, deep-space communications, and continues to be used in R/C systems.