In article Bear writes:
Bob,

I don't believe that we switch to GSM or whatever.

1. For none of the digital communication techniques it was possible to
find a global frequency range.

Seems unlikely. Are you saying that there is no VHF or UHF band available
worldwide?


2. The relative speed is too high. To my knowledge the highest speed to
which a digital communication system is certified is 500 km/h (310 mph).
This is GSM-R, Global System for Mobile Communications - Railway or
GSM-Railway, for details see Wikipedia.
500km/h would be good enough for us but not for others. We can forget it
in aviation thanks to Doppler effect.

Bear

Hmmm. The prime communications channels with the space station are digital.

DirecTV and Dish Network are digital. The network feeds to your TV stations
are digital via satellite. The "cable channels" are fed digitally to your
cable companies.

GPS is digital. It seems to be popular in aircraft.

Alan