  Providing connectivity to unmanned aerial vehicle-user equipments such as
drones or flying taxis is a major challenge for tomorrow cellular systems. In
this paper, the use of coordinated multi-point transmission for providing
seamless connectivity to UAV user equipments is investigated. In particular, a
network of clustered ground base stations that cooperatively serve a number of
UAVUEs is considered. Two scenarios are studied: scenarios with static,
hovering UAV user equipments and scenarios with mobile UAV-UEs. Under a maximum
ratio transmission, a novel framework is developed and leveraged to derive
upper and lower bounds on the UAV-UE coverage probability for both scenarios.
Using the derived results, the effects of various system parameters such as
collaboration distance, UAVUE altitude, and UAV-UE velocity on the achievable
performance are studied. Results reveal that, for both static and mobile UAV
user equipments, when the BS antennas are tilted downwards, the coverage
probability of a high-altitude UAV-UE is upper bounded by that of ground users
regardless of the transmission scheme. Moreover, for low
signal-to-interference-ratio thresholds, it is shown that CoMP transmission can
improve the coverage probability of UAV user equipments, e.g., from 28% under
the nearest association scheme to 60% for a collaboration distance of 200m.
