Hi Mike,
I think that you are misunderstanding what IPD is and does. Personally I think that the phrase "post processing" is a little misleading. To all intents and purposes IPD does the same as PCM. PCM filters each frame before passing it to the decoder. If it sees a dodgy frame then that frame is blocked. The difference is simply that PCM and IPD use a different set of papameters to determine if the frame is good or not. The pertinent word in IPD is the first one-"Intelligent". Rather than encode the signal in a numeric format, modern processers can be programmed to recognise a good signal from a bad one, on a number of different parameters, do this in real time and offer slightly more than PCM. For example, one of the points detractors of pCM make in this debate is that PCM will mask any problems until it is too late. They have a point. With the latest generation of MPX IPD Synth Rx's you can turn off the IPD filter to perform a range check. Swith off and on again and the filter is restored. Now you can do another range check. If there is big discrepacy between the range with the filter on or off then you need to take a closer look because something is wrong. There also seems to be a slightly "softer" regime ragarding failsafe, where the reciever finds itself in the grey area between a good signal and an entirely bad one. What the IPD one does during this short period is follow the trend of the previos pulses and "fill in the gaps" as it were. However this slows the servos down whilst it is doing this. The effect in practice is that you get ( n these particular circumstances, or on the edge of radio range) a few moments of sluggish response, which warns you of a problem.
In my experience with IPD recievers ( I was amongst the first people to use these in the UK) there is little to choose between these and PCM in practice, except for a slightly faster servo respnse from IPD. (which is why I use IPD in my jets and keep my PCM for my big scale gliders) They do exactly what its says on the tin.
One further point. I have done some impirical testing of PCM vs PPM rx's in the past regarding there interference rejection capabilities. Here I agree with your earlier post. I break down the test into 3 catagories: 1) light interference, 2) moderate interference, 3) major intereference. Results were 1) PPM = Glitches, PCM = no effect at all. 2) PPM =Serious glitches, probally would result in a crash with most models, PCM = momentary failsafe followed by periods of control, you have a chance of controling the model. 3) PPM = Servos fully locked over, the model is doomed, PCM Rx in failsafe.
The same test with IPD has proved more or less the same results. The point is that these tests give the lie to the idea that with a straight PPM reciever that the flyer will fight through the interference, but a PCM RX will enter a lockout condition. IMO, from these tests, whilst they PCM/IPD equipped plane may be cruising gently to oblivion, the equalilent PPM equipped plane has already rekitted itself on the runway. Whilever your model is flying there is a chance that the interference will cease and you can recover. I speak from experience, this has happened to me with a D/F model.
Regards,

John