Pulse Position Modulation (PPM)
What is Pulse Position Modulation?
Pulse Position Modulation, sometimes known as pulse phase modulation is used for digital signal transition. It is used in fibre optics and IR (infrared) remote controls where there is a lack of interference, It is a technique that uses pulses of the same breath and height but is displaced in time from some base position according to the amplitude of the signal at the time of sampling.
Pulse Position Modulation VS. Pulse Ampltude Modulation (PAM) and Pulse Duration Modulation (PDM)
PPM is superior to PAM and PDM in the sense that it has a higher noise immunity since the only thing the receiver needs to do is to detect the pressure of the pulse at the correct time. The duration and amplitude of the pulses are irrelevant.
Pulse Amplitude Modulation (PAM), like PPM is a form of signal modulation where it differs the message information is encoded in the amplitude of a series of signal pulses. PAM is an analogy pulse modulation scheme in which the amplitude of train of carrier pulse is varied according to the sample value of the message signal. Pulse Duration Modulation (PDM), is a pulse modulation technique that transmits analogue signals. It is not reliant on the height of the pulse but does depend on its duration.
Uses of Pulse Position Modulation
PDM is used for numerous functions in modern everyday life. Satellite laser ranging stations determine distances to satellites by measuring the time of flight of short laser pulses. The laser repetition rates vary from 10Hz to 2 kHz. At many stations, software is upgraded to modulate the, usually constant and steady, interval between laser pulses. Using such a PPM scheme, people can successfully transmit text files via a great distant back to a multi-pixel photon counting module in a receiver telescope.
With such a setup at any SLR station, and a right detector, plus simple time tagging electronics at low earth orbiting satellites, it is possible for any satellite laser ranging station to transmit data to oany satellite, even during standard SLR tracking. As this technique is easy to set up and does not affect routine SLR tracking, it can be applied to upload data to satellites, using the more than 30 available satellite laser ranging stations around the world, and with higher data rates than some of the conventional uplinks.
Other types of Pulse Modulations
As already mentioned, there are many variations on the Pulse Modulation system. Perhaps the most important one of these is Pulse Code Modulation (PCM). About in the middle of the eighties, the arrival of a cheap microprocessor technique finally made it possible to protect the sensitive part of the transmission chain from errors by special encoding. Of course this means that the transmitter and receiver both need a processor to complete this task, These microprocessors have become extremely small. The simple binary (two state) transmitter people were already using doe PPM is perfectly suited to the task of transmitting 1 and 0 sequences. However, people did not want to give up on the accuracy and frame rate of PPM.
Reasons why: We chose the topic of Pulse Position Modulation as we were all unfamiliar with it and wanted to look into and find out what it was all about. Also, it was listed in the music category which all three of us in our group share a mutual interest in.
Finding Info: Initially we looked the topic up on wiki just to get a rough idea of what the topic was about. After that we wanted to find a similar topic to compare it to. After much research we found a video on YouTube that is linked in our references below, showing the comparison of our topic VS another similar topic. Finally we looked up papers and journals on Google scholar for our over all collective information.
Use of resources: We used the wiki page to get a rough idea of what the topic was about and how it functioned. The YouTube page was used to compare our chosen topic to the similar topic Pulse Width Modulation. And finally we used the journals and papers that we found on Google Scholor to acquire a greater understanding of the topic we were studying.
1. M.R Pearlman, J.J. Degnan, J.M Bosworth, (2002); "The International Laser Ranging Service" Advances in space research, Vol. 30, No.2
2. A,Kumar, V.K JAIN (2008); "Antenna Aperture Averaging and Power Budgeting for Uplink and Doownlink Optical Satellite Communication". Jan 4-6, 2008, pg 126 - 131.
3. John Donovan (2009); "Portable Electronics: World Class Designs", pg 161.