Underlay Cognitive Radio Millimeter-Wave Spectrum Access for In-Building Dense Small Cells in Multi-Operator Environments Toward 6G

Abstract

In this paper, we propose an underlay cognitive radio spectrum access (UCRSA) technique to share the licensed 28 GHz millimeter-wave (mmWave) spectrum of one mobile network operator (MNO), termed as primary MNO (p-MNO), with small cells in a building of another MNO, termed as secondary MNO (s-MNO), in a country. The proposed UCRSA considers operating each in-building small cell of an s-MNO at the maximum transmission power on its licensed spectrum, whereas at a reduced transmission power on a shared spectrum of any p-MNO at any time. The reduction in the transmission power varies in accordance with the predefined interference threshold set by the corresponding p-MNO. We derive average capacity, spectral efficiency (SE), and energy efficiency (EE) and carry out extensive numerical and simulation results and analyses for an s-MNO of a country consisting of four MNOs. It is shown that UCRSA can improve SE by 2.67 times, whereas EE by 72.74%, of the s-MNO as compared to that of the traditional static licensed spectrum allocation (SLSA) technique that allocates each MNO an equal amount of 28 GHz mmWave spectrum. Finally, we show that the proposed UCRSA technique can satisfy the expected SE and EE requirements for sixth-generation (6G) mobile systems by reusing the licensed, as well as shared, 28 GHz mmWave spectra of the s-MNO to its small cells of 71.8% less number of buildings than that required by the traditional SLSA technique.