# On the Performance of a UAV-Aided Wireless Network Based on NB-IoT
## 1 Introduction  
Machine-type communications have witnessed a renewed interest from the scientific community thanks to advancements in technology and the plethora of new applications involving them. Statistical reports already proved a steady increase in the number of machine-type or Internet of Things (IoT) links (see, e.g., [[https://www.statista.com/statistics/802690/worldwide-connected-devices-by-access-technology/](https://www.statista.com/statistics/802690/worldwide-connected-devices-by-access-technology/)]([https://www.statista.com/statistics/802690/worldwide-connected-devices-by-access-technology/](https://www.statista.com/statistics/802690/worldwide-connected-devices-by-access-technology/)) or [[https://www.ericsson.com/en/mobility-report/reports/november-2019/iot-connections-outlook](https://www.ericsson.com/en/mobility-report/reports/november-2019/iot-connections-outlook)]([https://www.ericsson.com/en/mobility-report/reports/november-2019/iot-connections-outlook](https://www.ericsson.com/en/mobility-report/reports/november-2019/iot-connections-outlook)), accessed on 7 September 2021. ), but the massive presence of IoT devices might not be the only major challenge to be addressed for the future. Other key challenges lie on the more differentiated and stringent requirements on communication performance--the demand--imposed by the several applications and use cases possible. These may include autonomous vehicles, wearables, industrial IoT for Industry 4.0, data monitoring, alarm detection, municipality services and many others, in which one can observe that commonalities are few. These aspects call for new paradigms to network design. To avoid the densification and deployment of new terrestrial bases needing huge investments in capital and operational expenditures, a viable and largely foreseen solution can be found in mobile base stations (BSs). Unmmaned aerial vehicles (UAVs) (a.k.a. drones), where mobile BSs can be mounted, represent very interesting means to add the required flexibility and scalability for the future networks. UAVs have, in fact, the potential to fly on-demand and exactly where is needed. Moreover, they are not tied to roads, not affected by traffic congestion and canfeature good connectivity with both on-ground users and terrestrial BSs (i.e., backhaul), thanks to the large probability of being in the line of sight (LoS). The usage of UAVs as mobile BSs is especially suited for massive machine-type communication (mMTC) and IoT links, since IoT nodes are mostly static (do not change their position over time) and their traffic demand is usually predictable [1]. The knowledge of these two basic inputs allows to make decisions in advance on the trajectory to follow to maximize IoT service, plan periodical flights when the demand arises, modify the UAV behaviour if needed, and so on. This may be further relevant if these mobile BSs have to direct themselves in remote and different areas where the nodes are placed. To consider at our best a scenario with the plurality of IoT applications mentioned before, as pictured in Figure 1, we consider a massive number of IoT devices scattered in different zones of a service area, requesting to transmit a periodical packet. This is a realistic scenario, and perfect for UAV services during a single flight. Thanks to their versatility, flying network nodes like UAVs have gained an ever-increasing interest from researchers concerning standardization bodies. The 3 rd Generation Partnership Project (3 GPP), after considering the feasibility of UAVs being user equipment (UE) (i.e., end users of the cellular network), started approaching on-board radio access for UAVs (denoted with the acronym UxNB) at the beginning of Rel. 17 [2,3]. Because of the several activities considering the aid of UAVs to cellular users, we focus on the cellular radio access technology, as stated in the 3 GPP documents [4].