A Generic Millimeter Wave and Terahertz Spectrum Reuse Model for In-Building Multi-Band Small Cells: Achieving Spectral and Energy Efficiencies of 6G

This paper presents a generic spectrum reuse model (GSRM) to reuse millimeter wave (mmWave) and terahertz (THz) spectrum in multi-band-enabled small cells located within multi-story buildings to address high spectral and energy efficiencies of sixth-generation (6G) mobile networks. For mmWave and THz bands, we consider 28 GHz, 142 GHz, 250 GHz, and 300 GHz bands, and each small cell is assumed to be equipped with these multiple bands. In developing GSRM, we first characterize interferences to derive a minimum distance between apartments of co-channel small cells at both intra-floor and inter-floor levels for each band leading to the formation of a 3-dimensional (3D) cluster of apartments such that the whole spectrum of the corresponding band is allocated to small cells within the cluster. The same spectrum is reused further in small cells of all adjacent 3D clusters within the building. We consider a random distribution of small cells within each 3D cluster. Two scenarios are considered where scenario 1 has the same 3D cluster size for each band, and scenario 2 considers different 3D cluster sizes corresponding to the respective band. We formulate the spectral efficiency (SE) and energy efficiency (EE) metrics of the proposed GSRM in a multi-tier network and develop an algorithm to evaluate its SE and EE metrics. With extensive system-wide evaluations, we show that compared to scenario 1, the overall SE and EE in scenario 2 are improved by 33.33% and 4.5%, respectively, and the proposed GSRM can achieve the prospective SE and EE requirements for 6G mobile systems.