A crucial 6G technology will be the sharing of almost all currently licensed spectrum. Watch the video below with Durga Malladi of Qualcomm if you have any doubts. Wi-Fi proved that spectrum sharing works, doubling or tripling effective capacity. LAA convincingly shows that commercial quality broadband can be delivered today over unlicensed spectrum. Verizon, AT&T and Qualcomm did the testing to confirm this. The same technology can be used to recover spectrum in licensed bands like 1800 & 2100,
60-80% of the spectrum now a licensed monopoly can be shared - if the regulator has the confidence to require it. ?20-40 Mhz would need to be reserved for control plane signaling and emergency use. The original telco might claim priority but the spectrum they aren't using can be shared. Rarely is more than 40-70% in use.
Especially in rural areas, massive amounts of licensed spectrum lie fallow. It would be enough, for example, to deliver a true gigabit of rural broadband.
LAA (Licensed Assisted Access) uses a control channel in licensed spectrum. AT&T is rolling it out later this year. That uses a sliver of licensed spectrum as a control channel and connects in other bands for capacity. Qualcomm has a similar system called MultiFire that works for new entrants because it doesn't require licensed spectrum.
Columbia Professor and FCC CTO Henning Schulzrine, believes "All new spectrum would be shared." Circumstances and estimates vary, but sharing spectrum usually at least doubles capacity.