Coverage Performance of the Terrestrial-UAV HetNet Utilizing Licensed and Unlicensed Spectrum Bands

To address the spectrum shortage issue, the technology of sharing the unlicensed spectrum resource has been developed for terrestrial wireless networks, e.g., the New Radio Unlicensed technology. Recently, due to the limitation of terrestrial wireless networks, unmanned aerial vehicles (UAVs) have been proposed to improve the coverage for users. Hence, the combination of the unlicensed spectrum band technology and the UAV communication can fulfill the requirements of offering 3-D coverage while improving the spectrum efficiency. In this paper, we investigate the terrestrial and UAV heterogeneous network (HetNet), where both the terrestrial base stations and aerial base stations implement the random mode selection procedure to use either the licensed or unlicensed spectrum band. Based on stochastic geometry, we develop a tractable mathematical framework to characterize the medium access probability and the overall coverage probability. The accuracy of the analytical evaluations is validated by simulations. Our results show that the incorporation of the licensed and unlicensed spectrum band by using the mode selection scheme can improve the overall network performance, compared with the performance of the 3-D HetNet operating in the licensed spectrum band only. Furthermore, mode selection of the aerial network plays the dominant role in improving the overall coverage probability, and the mode selection probability (i.e., the probability of switching to use the unlicensed spectrum band) has to be selected carefully to maximize the overall coverage probability.