Outage Analysis for Millimeter-Wave Fronthaul Link of UAV-Aided Wireless Networks

Unmanned Aerial Vehicle (UAV)-wireless networks represent a promising solution to expand the reach of mobile connectivity beyond current boundaries. When Distributed Units (DUs) are deployed on the UAV, the high rate requirement on the wireless Fronthaul (FH) link between the UAV-DU and the terrestrial network poses a major challenge. To address the capacity demand of the FH network, we investigate the outage probability at millimeter Wave (mmWave) and sub-6 GHz frequency for different blockage environments and UAV heights. Utilizing a stochastic geometry framework, we first derive analytical approximate expressions for the outage probability of the FH link and we observe generally a good agreement with the simulation results for different UAV heights. In addition, numerical results for different urban densities show that the FH outage probability is minimized choosing an optimal UAV-DU altitude. We further analyze the impact of the antenna gain for two candidate mmWave frequencies on the FH link. High mmWave bands need sharp directional beamforming and large transmit bandwidth to outperform low mmWave bands in term of rate outage. Finally, our results show the impact on the outage probability of the FH overhead, that scales with the number of antenna elements, for different protocol splits.