Coverage Analysis and Optimization of UAV Networks with Directional Antennas

In this paper, we study coverage probability of UAV cellular networks, where the aerial base station is equipped with the directional antenna. The cellular user on the ground has the omnidirectional antenna and connects to the nearest base station. We derive the explicit expression of lower bound of downlink coverage probability based on Rayleigh fading channel and height dependent path loss exponent model. Our analytical and numerical results show that the directional antenna performs a beneficial role in reducing interference and improving the coverage probability. Furthermore, we conduct the system optimization to explore the behavior of optimal density, altitude and antenna beamwidth. We find that the optimal density decreases with an increase in UAV altitude and the approximation matches the simulation result well, which helps to optimize the system design with tractability.