## 2 Hardware Components
We have included it in our solution to provide for a reliable communication method in hard-to-reach areas so as to ensure a minimum communication bandwidth for distress signals and the output of vital sign sensors. The concentrator is a custom-built one, based on the Raspberry Pi 3 Model B+ [16] Single Board Computer (SBC) and the RAK2287 [17] LoRa modem. The node can be powered using either Power over Ethernet (PoE) or by its own rechargeable battery, which provides for more than 2 days of continuous operation. We have designed and 3D printed an enclosure to accommodate the aforementioned parts in a single component, depicted in Figure 2. The SBC enables us to use an open-source software LoRaWAN stack, ChirpStack, and set it up locally. Consequently, the concentrator does not need internet access to communicate with a remote LoRaWAN network server for its operation and is self-sufficient. Mobile broadband modemBroadband cellular networking is the most ubiquitous form of wireless internet connectivity used in our everyday lives. Despite this, in cases of emergencies, it has been noticed that there can be low availability or interruptions of service due to damage or overloading of the internet service provider's infrastructure. Still, it is a cost-effective and worldwide available service, and our system should be able to take advantage of it whenever possible. Consequently, our system incorporates a 4G router, the Teltonika RUT950 [18]. It is a high-performance cellular router featuring dual SIM with auto-switch capability in cases of weak signal or data connection failure, designed as a Main/Backup internet source. The operation of the 4G router is augmented by an external 4G LTE 2X2 Multiple Input, Multiple Output (MIMO) omnidirectional antenna with a gain of 12 dBi. The relaxed space restrictions and the know orientation of the antenna permit the use of an antenna with more gain than the ones installed in cellphones leading to better signal-to-noise ratios and thus, higher data transmission rates. The modem itself is installed inside the central communication node. Point to Point link.Point to Point microwave links enable the connection of fixed locations separated by large distances while offering low latency and high bandwidth. The inclusion of a Point-to-Point link adds to the versatility and resilience of our solution because it can be used to address different needs that may arise during a USAR mission. Its inclusion provides an extra WAN interface to exploit the availability of internet connectivity at some remote but still reachable location, enables the provision of connectivity at a secondary location not covered by the WLAN (such as a UAV ground control station), or the connection of additional APs to the base station via a wireless backbone. The latter  
Figure 2: (**a**) Exploded 3D view of the LoRaWAN concentrator. (**b**) Real life realization. The SBC with the LoRa hat can be seen on the left of the black colored battery on the op right. provides the means to extend the system on the fly and interconnect distant areas of operations. The long-range and high data rate communication capabilities can be mainly attributed to the directive antennas utilized at both ends. The greater the antenna gain, the higher the effective radiated power and, as a result, the distance that can be bridged for a given bandwidth. Antennas are passive elements that create gain by focusing signal radiation at a particular area, meaning there is an inverse relation between gain and antenna beamwidth. Narrow beamwidths lead to prolonged and, at times, not successful antenna alignment procedures, and consequently, a compromise must be made between antenna gain and ease of installation. The airMAX NanoStation AC 5 GHz radio [19] with a 3 dB beamwidth of 45 degrees and gain of 16 dBi, has been chosen. It is a ready-to-use solution for Point-to-Point links and is able to bridge considerable distances if adequate ground clearance is provided.