Closed Form Approximations for UAV Line-of-Sight Probability in Urban Environments

This paper presents a new approach to estimate the probability of line-of-sight (LoS) for unmanned aerial vehicle (UAV) communications. We provide lower and upper bounds on the probability of LoS in terms of what we call the first-building-LoS probability. We provide a statistical model for the ground distance to the first building along the line from the user to the UAV. Based on this we provide a general formula for the first-building-LoS probability for urban environments where the building heights follow a Rayleigh distribution. We show that the first-building-LoS probability is a good estimate for the probability of LoS. Our closed-form formulas estimate the probability of LoS significantly more accurately than the existing approaches. We also obtain closed-form estimates of Area Line-of-Sight Probabilities for a scenario in which the UAV provides coverage to a circular region on the ground.