## 2 Related Works  
The concept of hybrid networking within the IoT domain has been discussed in a number of papers. Before the emergence of LPWAN facilities, the cooperation of different radio technologies was already evaluated within Wireless Sensor Network (WSN) architectures, for example combining ZigBee and Ultra Wide Band to differentiate data transmission according to the specific application requirements [12]. The rise in LPWANs has paved the way to the implementation of massive and dense network architectures, with an exponential growth in the number and complexity of interconnected devices that act as drivers for the definition of future communication techniques [13]. In this context, the combination of multiple radio technologies was considered a viable solution to create modular networks to satisfy different intricacy levels. Focusing on the two technologies exploited in this paper, some examples of hybrid networks emerge for both, with a prominence of LoRaWAN-based solutions. A theoretical approach focusing on the integration of different LPWANs forming hybrid networks is proposed in [14]: while the actual implementation of the network is not described in detail, the proposed architecture is prone to the integration of the most LPWANstandards in cooperation with other cellular (i.e., LTE) and non-cellular (i.e., Wi-Fi) data transmission technologies. Hybrid LoRaWAN solutions were proposed with a number of communication techniques: however, most examples in the literature mainly leverage the Long Range (LoRa) physical layer, without implementing a full LoRaWAN infrastructure. An obvious integration is the one with Bluetooth Low Energy (BLE), thus combining low power local area and wide area connectivity: in [15], BLE was employed to set up local data transmission among nodes that were integrated in LoRa clusters, while BLE connectivity was seen as a local area extension of a LoRa network in [16]. Finally, an integration at the physical layer between the two technologies was proposed in [17]. In parallel with LoRa, NB-IoT was also integrated with BLE: in [18; 19], both channels were simultaneously exploited for data transmission according to a multi-modal paradigm that was based on the optimisation of power consumption. The extension of a LoRaWAN network with short range connectivity was also discussed in [20], where LoRaWAN Class A devices were integrated with Wake up Radio (WuR) low-power radio modules that were ad hoc designed to consistently reduce the power consumption of the edge segment of the network. LoRa networks were also integrated with other wide area technologies: while the standard configuration of a LoRaWAN network foresees the presence of an Internet connection between Gateways and Server, that is in general set up with Ethernet, WiFi or 4G connections, some work focused on architectures where this link was set up via satellite [21] or Fifth Generation (5G) cellular connection [22]. In the context of 5G connectivity, [PERSON] et al. [23] applied the concept of multiple Radio Access Technologies (Multi-RAT), whilhc was successively extended to LoRa and 4G in [24]. The concept of Multi-RAT has been recently expanded to the convergence of LoRaWAN and NB-IoT into hybrid networking: in particular, in [25], a theoretical analysis was carried out to assess the achievable benefits with the implementation of this kind of infrastructure, while in [26], a prototype of a hybrid LoRaWAN-NB-IoT node was described and tested, mainly in terms of power consumption. However, with respect to the one proposed in this work, the systems described in [25; 26] were basically end devices provided with both data transmission technologies: the two channels could be used alternatively or in parallel but were not integrated to set up a hybrid channel. Together with these two works, only another contribution addresses the combination of these two technologies by proposing the design of a very simple LoRa-NB-IoT Gateway for packet forwarding scopes [27].