# On Analyzing Routing Selection for Aerial Autonomous Vehicles Connected to Mobile Network
## 3 Motivation
### Description of the Scenario and Tests of Communication Based on Mobile Network  
Our scenario includes an unmanned aerial vehicle Birdie UAV that develops transmission links established through 4G mobile network. In particular, mobile communication covers transmitting control and telemetry signals based on a compact 4G modem with USB 2.0 interface with dimensions that should not exceed 100 \(\times\) 30 \(\times\) 15 mm and maximum weight of 40 g.  
The additional control station (also called ground station) is equipped with Mission Manager software and a configured VPN client that allows to establish a secure, encrypted connection to the drone over any internet connection (overlay encryption). The control station is also connected to the Internet through a mobile network. So, our scenario contains two radio links: On the one hand UAV to antenna, and, on the other hand, control station to antenna. Normally, these two radio links are not situated in the same segment of the antenna [20] (one segment is pointing to the air and the other pointing to the ground), so we can assume that the two radio links are independent as far as resource usage is concerned. MAVlink communication (telemetry and control) is transmitted directly through UDP streams. The level of network latency shown in the current (4G) generation of mobile networks was around 200 ms (average), which is acceptable for controlling the implementation of UAV missions [21]. It is assumed that the flight works in the supervisory mode, i.e., without the necessity of direct control of steering surfaces by the operator. Flight modes such as FBWA or CRUISE can be safely used to maintain the link latency at a level not exceeding 300-500 ms, while for flight modes such as LOITER, RTL, AUTO, and GUIDED even delays of 1-2 s still allow a secure mission execution. It has to be underlined that implementation of this type of operations requires the presence of a VLOS operator to carry out the drone's launching and landing processes. The quantitative evaluation of communication link quality has been limited to monitoring of link delays. For the tests, the UAV is equipped with NanoPi Neo Core 2 on-board computer, based on 4 core ARM Cortex A53 processor with clock frequency up to 1.5 GHz. The load of the processor during work with the first version of the software was about 25% (i.e., 100% on one of the 4 cores). After re-designing the on-board software, it was possible to reduce processor consumption to about 4-5% in a continuous operation mode [22]. This optimization was particularly important due to the avionics chamber heat management. The whole range of navigation functions as well as the current monitoring of the state of the airborne components were carried out by the Autopilot module with integrated sensors. The hardware platform is Pixhawk version 1 (PX4 v2 project with ETH Zurich), providing support for all peripherals based on the NuttX OS real-time system. The software used for flight is a modified ArduPilot package with \"PX4 Middleware\" libraries. The communication with the mobile network is ensured by the installation of MF823 on-board modem, which provides support for 2G/3G/4G networks [23]. The modem is mounted in a chamber under the hatch of the battery, while maintaining the ability to access the modem on the ground without having to cut the power supply from the Birdie UAV set. The status of the network connection is signalized by a LED that indicates the availability of the network. Possible connection statuses according to the status of the LED are: (1) Red: modem on, but not logged into any network, (2) Green blinking: Modem connected to LTE network, (3) Green continuous: Modem logged into LTE network, (4) Blue blinking: Modem connected to 2G/3G network, and (5) Blue continuous: Modem logged into 2G/3G network.