Hi,
UWB sounds great. Nearly unlimited numbers of users. Robustness against reflection and fading. Adaptive data rate...
But there is one point. Think how long it takes to synchronize a pattern which is known at TX and RX with a length of e.g 2^20. How much energy are loost for syn. How accurate synchronisation must stay.
In the beginning of the 20. century the mechanics of coils and caps define the channnel in FDMA. With UWB atomic clocks have to be used to stay on the channnel!!