Inter-HAP Based Geometrical 3-D Channel Model Operating at 28 to 60 GHz for Future 6G Non-Terrestrial Networks

This paper presents a geometrical 3-D channel model for stationary inter-high altitude platform (HAP) systems operating at millimeter wave (mmWave) frequency bands for the future 6G non-terrestrial networks (NTNs). The motivation of this study is to satisfy such a scenario where a high data rate between two HAPs is desired. In order to do this, the possible reasons for path loss, namely the free space and atmospheric path losses that are severely observed because of the short wavelength of the mmWave signals, are characterized according to 3GPP standards and ITU recommendations. Unlike most of the air-to-air unmanned aerial vehicle (UAV) channel modeling studies where a 2-D channel model is adopted, this study adopts a 3-D approach to characterize the wireless channel between two HAPs to fill the gap in the literature and reflect the actual characteristics of the air-to-air UAV networks. Moreover, this paper introduces the usage of the multiple input multiple output (MIMO) beam-forming technology in the UAV networks to compensate for the path loss effects in mmWave bands. Numerical results show the validation of the proposed 3-D channel model in point-to-point HAP networks at frequencies varying from 28 to 60 GHz.