# Cellular and Virtualization Technologies for UAVs:
## 3 Testbed Components Description
### Cellular-Assisted UAV Communications  
To support research activities, this publication proposes a novel communication model for this testbed that can be on-boarded as the payload of almost any UAV (we have used small UAVs to verify this fact). This prototype incorporates a Raspberry Pi 4 (RPi) (Raspberry Pi 4 Model B: [[https://www.raspberrypi.org/products/raspberry-pi-4-model-b/](https://www.raspberrypi.org/products/raspberry-pi-4-model-b/)]([https://www.raspberrypi.org/products/raspberry-pi-4-model-b/](https://www.raspberrypi.org/products/raspberry-pi-4-model-b/)) (accessed on 27 April 2020)) Single Board Computer (SBC). The RPi can be equipped with one of these two alternatives to connect with the cellular network: (i) the Sixfab 3G/4G& LTE Base HAT (Raspberry Pi 4G/LTE Cellular Modem Kit: [[https://sixfab.com/product/raspberry-pi-4g-lte-modem-kit/](https://sixfab.com/product/raspberry-pi-4g-lte-modem-kit/)]([https://sixfab.com/product/raspberry-pi-4g-lte-modem-kit/](https://sixfab.com/product/raspberry-pi-4g-lte-modem-kit/)) (accessed on 27 April 2020)), or (ii) a 5G/4G/3G HAT (SIM8200 EA-M2 5G HAT: [[https://www.waveshare.com/sim8200](https://www.waveshare.com/sim8200) ea-m2-5g-hat.htm]([https://www.waveshare.com/sim8200](https://www.waveshare.com/sim8200) ea-m2-5g-hat.htm) (accessed on 27 April 2020)). The RPi acts as the brain of the UAV, having the ability to host different network designs and configurations to enable its communications, i.e., this device  
Figure 2: High overview of the proposed testbed. allows the use of any protocol or communication solution to establish communications with other devices or/and the Internet, for example implementing a Virtual Private Network (VPN) tunnel. Moreover, the HATs provide the RPi with a simple interface bridge between mini PCIe cellular modems. Three different modems have been selected for this system: the Telit LE910C1 Mini PCIe LTE CAT1 Module (Telit LE910C1 Mini PCIe LTE CAT1 Module: [[https://sixfab.com/product/telit-le910c1-mini-pcie-cat1-lte-module/](https://sixfab.com/product/telit-le910c1-mini-pcie-cat1-lte-module/)]([https://sixfab.com/product/telit-le910c1-mini-pcie-cat1-lte-module/](https://sixfab.com/product/telit-le910c1-mini-pcie-cat1-lte-module/)) (accessed on 27 April 2020)), the Quectel EC25 Mini PCIe 4G/LTE Module (Quectel EC25 Mini PCIe 4G/LTE Module: [[https://sixfab.com/product/quectel-ec25-mini-pcie-4g-lte-module/](https://sixfab.com/product/quectel-ec25-mini-pcie-4g-lte-module/)]([https://sixfab.com/product/quectel-ec25-mini-pcie-4g-lte-module/](https://sixfab.com/product/quectel-ec25-mini-pcie-4g-lte-module/)) (accessed on 27 April 2020)) (both compatible with the Sixfab HAT), and the SIMCom SIM8200-M2 (compatible with the Waveshare HAT), allowing its straightforward configuration to start using cellular internet with the RPi. All equipment is powered with a portable battery of 3.7V and 3800 mAh. This equipment can be appreciated in Figure 2(a). Despite establishing connectivity with the commercial cellular network, communications cannot still be enabled between the UAV-controller and the device since the HATs assign a private IP address to the RPi, independently of the IP address that the PCIe modem uses to connect to the network (provided by the commercial operator). In consequence, all the communications between the RPi and the exterior (i.e., Internet) are performed using a Network Address Translator (NAT) (included in the HAT). By extension, the RPi can communicate with the UAV-controller (as the UC3M network provides public IP address), but not in the reverse direction, as private IP addresses are not directly reachable from the Internet (i.e., the NAT is preventing the UAV-controller from reaching the RPi). Unfortunately, the HATs do not allow port opening or port forwarding configuration. In order to solve this issue, since the UAV-controller must be able to communicate with the RPi, the testbed will utilize a VPN service where all the UAS equipment is connected in order to enable a relay service.