  The rapid growth of active wireless communications technologies has fostered
research on spectrum coexistence worldwide. One idea that is gaining attention
is sharing frequency bands solely devoted to passive applications, such as
passive remote sensing. One such option is the 27 MHz L-band spectrum from
1.400 to 1.427 GHz. Active wireless transmissions are prohibited in this
passive band due to radio regulations aimed at preventing Radio Frequency
Interference (RFI) on highly sensitive passive radiometry instruments. The Soil
Moisture Active Passive (SMAP) satellite, launched by the National Aeronautics
and Space Administration (NASA), is a recent space-based remote sensing mission
that passively scans the Earth's electromagnetic emissions in this 27 MHz band
to assess soil moisture on a global scale periodically. In this paper,
leveraging stochastic geometry, we assess the feasibility of using this passive
band for the downlink (base station to user equipment) of a large-scale
terrestrial NextG wireless network exposed to SMAP, while ensuring that the
error induced on SMAP's measurements due to RFI is below a given threshold.
Although the methodology established here is based on SMAP's specifications, it
is adaptable to various passive sensing satellites regardless of their orbits
or operating frequencies.
