ORIGINAL: JohnMac
IPD is the replacement technology for PCM. Multiplex were first to introduce PCM, and now are the first to move on from PCM. IPD will work with any PPM transmitter, work at PPM speed (not slowing the servos like PCM does) whilst giving the interference rejection and failsafe qualities of PCM.
When PCM was introduced the only way of the Rx scruitising the incoming signal was first to give the signal a digital numeric value. Technology has moved on and modern processors can interrogate the signal in real time (hence the speed improvement). The algorithm can tell the difference betwwen a good signal frame and a bad one. Moreover, it can take various stages of action in the event of a poor signal, ranging from just waiting for the next frame up to full failsafe. However, in the event of a few bad frames, these can be "fixed" by the Rx storing the signal trend. This has the effect of slowing the servo response before the model gets to the point were the signal is so bad that failsafe cuts in, so you get some warning of the problems.
I hope this helps,
John
I have had a single conversion IPD receiver that I have used for several years with no problems.
However I think PCM is better because each word (pulse) contains its ID. That makes each pulse independent. Since interference is random in nature and not synchronized with the frame the next interference pulse is not likely to occur in the same PCM word. Thus the PCM receiver will continue to work after a receiver that depends on the integrety of the frame has quit working - especially those control pulses at the end of the frame.
If you get interference that is heavy enough to wipe out the PCM receiver the PPM (IPD) receiver will be long dead. If that's an advantage I don't see it.