Given the same RF section and demodulation scheme of raw data there is actually a very small window of RF interference where it makes any difference at all whether you have PCM or PPM. i.e a poor signal will have to be very consistent at some level for PCM to give you better control. In practice this does not happen. PCM has a benefit over PPM but it is NOT a significant improvement in dataling security. However PCM under transient glitching is safer because the aircraft can be made to behave more predictably during those instances and is therefore the preferred scheme for jets. Another important factor is that the demodulation of PCM is more resistant to power bus noise from multiple digital servos. The analog nature of PPM demultiplexing is often very prone to power glithes. These tend making the servo to glith even more and you have an unstable system. Under these conditions the RF section of the RX also suffers from this noise. So it kills itself. THIS IS THE MOST IMPORTANT BENEFIT OF PCM...
I am busy with an R/C system that is not subject to general interference at all. The technology is not new but has never been taken up by R/C mnfs due to cost. However the cost has reduced significantly over the last few years making it viable to have a duplex link with 100 times the bandwith of PCM. It is FCC approved and requires no frequency control or peg system... Its not science fiction, we are using it on UAV,s as the default choice.
Imagine as many channels as you can put servos in a plane, feedback of inflight data, airspeed, altitude, battery and engine status.
All for less than $2000
Andre Baird