  The millimeter wave spectra at 71-76GHz (70GHz) and 81-86GHz (80GHz) have the
potential to endow fifth-generation new radio (5G-NR) with mobile connectivity
at gigabit rates. However, a pressing issue is the presence of incumbent
systems in these bands, which are primarily point-to-point fixed stations
(FSs). In this paper, we first identify the key properties of incumbents by
parsing databases of existing stations in major cities to devise several
modeling guidelines and characterize their deployment geometry and antenna
specifications. Second, we develop a detailed uplink interference framework to
compute the aggregate interference from outdoor 5G-NR users into FSs. We then
present several case studies in dense populated areas, using actual incumbent
databases and building layouts. Our simulation results demonstrate promising 5G
coexistence at 70GHz and 80GHz as the majority of FSs experience interference
well below the noise floor thanks to the propagation losses in these bands and
the deployment geometry of the incumbent and 5G systems. For the few FSs that
may incur higher interference, we propose several passive interference
mitigation techniques such as angular-based exclusion zones and spatial power
control. Simulation results show that the techniques can effectively protect
FSs, without tangible degradation of the 5G coverage.
