# Aerial Coverage Analysis of Cellular Systems at LTE and mmWave Frequencies Using 3D City Models
## 1 Introduction  
Unmanned aerial vehicles (UAVs) are getting more common and important in everyday life, but regulation typically constrains the use of UAVs to visual line of sight situations [1; 2]. The most important UAV applications, including search and rescue, packet delivery or autonomous surveillance, would require beyond visual line of sight operation. Inclusion of UAVs in Long-Term Evolution (LTE) networks has received significant interest in recent years, as this promises reliable coverage and good throughput, required for the beyond visual line of sight applications. Using cellular networks to provide connectivity to the UAVs introduces new challenges, for instance the resource sharing between aerial and ground users becomes a problem since the radio environment at high altitudes differs from the ground-level one. The analysis by Qualcomm in [3] is based on a large-scale measurement campaign and supports the viability of LTE commercial mobile networks for UAV operating beyond visual line of sight. In the report, it is shown that the signal quality of the downlink, from Base Station (BS) to UAV, was significantly lower for flying UAVs compared to the ground users: Signal-to-Interference-and-Noise (SINR) levels decrease up to 5 dB due to inter-cell interference. However, the SINR did not decrease to an extent that the UAVs had no coverage (defined as SINR \(\leq-6\) dB). The coverage outage probability was found to be very similar for UAVs and ground user equipment (UE) devices and it was concluded that commercial LTE networks should be able to support downlink communications requirements of the LTE-connected UAV deployment without modifications. In [4], the authors studied the feasibility of wireless connectivity for UAV user equipment via LTE networks. Moreover, propagation characteristics of base station to UAV communications were studied using measurements and ray tracing simulations in a rural area. They concluded that, for high altitudes propagation, conditions are close to free space and that at high altitudes downlink connections suffer from higher interference due to higher probability of LOS propagation of interfering base stations. Additionally, [PERSON] et al. [5] analyzed the impact of UAVs on the performance of an LTE network through simulations and measurements. They considered two scenarios, one where UAVs act as base stations, providing connectivity to ground users, and another scenario where UAVs act as users, connecting to a ground network. They studied the UAVs' impact on downlink and uplink performance of the ground LTE network. They concluded that interference would be the main limiting factor when introducing LTE enabled UAVs. The authors of [6] performed simulations and field measurements with a UAV in a rural area, evaluating the performance of aerial radio connectivity. They concluded that interference was one of the main limiting factors for both downlink and uplink connections, especially when load was high in the network. Two antenna mitigation techniques were explored. First, antenna beam selection was considered, where the UAV selected a directive antenna based on the location of its serving base station, and secondly interference cancellation was investigated, exploiting techniques to remove interference at the receiver. Alternatively a novel downlink inter-cell interference coordination mechanism was introduced in an effort to improve overall system performance and reliability, both for aerial and ground users. The measurements and simulations of [3; 4; 5; 6] show that interference was found to be the main limiting factor for different environments, in line with theoretical studies. However, the optimistic quality estimations presented in [3] could not be confirmed by [PERSON] et al. [4], [PERSON] et al. [6] and [PERSON] et al. [5]. Note that these works [3; 4; 5; 6] considered only rural and coast scenarios. The analysis in [7] describes the coexistence of aerial and ground users in cellular networks.