For the mobile phone use case, it seems like the transmitter would have to be emitting constantly in order to keep the base station appraised of its current position, for the purposes of computing the channel characterization. Otherwise, how would the base station know what transformations to perform on the outgoing signals to reach the mobile device in the event that a call is received? It's not like you could broadcast that information to everyone, because that would end up corrupting the spectrum for everyone else, which defeats the entire point of this system.
The whole scheme seems really dependent on knowing the position of all transmitters/receivers at all times.
The "paging channel" problem is already present in existing mobile radio systems. Solving it pretty much requires some form of TDMA — i.e. scheduled transmission — because only TDMA gives you the ability to actually power your radio off most of the time. Even Wi-Fi has features for this.
Why couldn't you reserve a tiny fraction of the bandwidth of the system (or some other but related spectra) for this sort of "calling transmitter #92" broadcast? Yeah, it'd impact everyone, but only finitely.
The whole scheme seems really dependent on knowing the position of all transmitters/receivers at all times.