Modeling Interference to Reuse Millimeter-wave Spectrum to In-Building Small Cells Toward 6G

In this paper, we present an analytical model to characterize co-channel interference between small cell base stations (SBSs), each enabled with dual-transceiver operating at 28 GHz and 60 GHz millimeter-wave bands, in a multistory building. Subject to satisfying a predefined co-channel interference limit, we then deduce a minimum distance in both intra-floor and inter-floor levels between co-channel SBSs. The optimal size of a 3-dimensional (3D) cluster of SBSs and the corresponding 3D spatial reuse factor are defined such that both millimeter-wave spectrums can be reused fully to each 3D cluster of SBSs within the building. We derive system-level average capacity, spectral efficiency, and energy efficiency metrics for an arbitrary number of L buildings of SBSs within a macrocell coverage. With extensive system-level numerical and simulation results, we show that the 3D spatial reuse of multi-millimeter-wave spectrums to each 3D cluster of SBSs per building can achieve the expected average spectral efficiency and average energy efficiency requirements for the sixth-generation (6G) mobile networks.