  The upper mid-band - roughly from 7 to 24 GHz - has attracted considerable
recent interest for new cellular services. This frequency range has vastly more
spectrum than the highly congested bands below 7 GHz while offering more
favorable propagation and coverage than the millimeter wave (mmWave)
frequencies. The upper mid-band can thus provide a powerful and complementary
frequency range to balance coverage and capacity. Realizing the full potential
of these bands, however, will require fundamental changes to the design of
cellular systems. Most importantly, spectrum will likely need to be shared with
incumbents including communication satellites, military RADAR, and radio
astronomy. Also, the upper mid-band is simply a vast frequency range. Due to
this wide bandwidth, combined with the directional nature of transmission and
intermittent occupancy of incumbents, cellular systems will need to be agile to
sense and intelligently use large spatial and frequency degrees of freedom.
This paper attempts to provide an initial assessment of the feasibility and
potential gains of wideband cellular systems operating in the upper mid-band.
The study includes: (1) a system study to assess potential gains of multi-band
systems in a representative dense urban environment and illustrate the value of
wide band system with dynamic frequency selectivity; (2) an evaluation of
potential cross interference between satellites and terrestrial cellular
services and interference nulling to reduce that interference; and (3) design
and evaluation of a compact multi-band antenna array structure. Leveraging
these preliminary results, we identify potential future research directions to
realize next-generation systems in these frequencies.
