## 3 Nodes' Configuration and Transmission Protocol  
Despite LoRa allows to considerably increase the radio coverage with respect to alternative solutions, the standard star topology cannot be applied to the scenario at hand. Indeed, the overall length of the \"Bottino Maestro di Fonte Gaia\" is around 15 km, whereas the transmission range of the LoRa modules in the \"Bottini\" environment is around 200 m, thus, forcing the choice towards a Linear Network with multi-hop communications. In particular, in the proposed architecture each sensor node is deployed at a distance of nearly 150 m each other. Hence, due to the limitations in the transmission range, each sensor node can directly communicate with adjacent nodes only. In this setting, a node acts simultaneously as an End Device transmitting its own data and as a Router forwarding the packets sent by the previous nodes, forming a chain from the first node down to the Gateway. To implement this kind of transmission protocol, the firmware of each node must be able to receive and transmit. LoRa allows to send packets either to a specific node through its own address, or in broadcast modality using address 0. Since in the proposed configuration each node is directly connected only to 2 nodes (the previous and the following ones), a natural choice leans towards the choice of broadcast modality. Indeed, the broadcast packet can be received by the subsequent node, but also by the previous one. This opportunity can be exploited to set up an overhearing mechanism which will be described in the following Section, with low power acknowledgement modality. It is worth noting that the proposed network topology is not intrinsically fault-tolerant. Indeed, a malfunctioning in one node blocks the transmission from all the previous nodes. Nevertheless, this chain-type data transmission makes the identification of the malfunctioning node very simple. Indeed, in the case a node is damaged, the Gateway will receive packets starting from the next node in the chain only. Hence, since the positioning of each node is known a priori, the malfunctioning node will be then easily identified. Due to the use of the broadcast modality, the substitution of the malfunctioning node will be totally transparent: the new node must simply be deployed in place of the old one without any network re-configuration. In the proposed network architecture, only two typologies of nodes are then possible: the Gateway node (Figure 4a) and the Sensor Node (Figure 4b). The Gateway node is the terminal node of the Linear Network and it is in general unique: it is only in charge of receiving all the packets and forwarding them to the data collection centre. However, it is the most complex node due to the presence of two types of connectivity. Hence, the Gateway to be deployed in the \"Bottini\" will be composed of a microcontroller, a LoRa module and a GSM module for data transmission. Figure 4: Architecture of (**a**) Gateway Node and (**b**) Sensor Node. The Sensor Nodes have basically the same setting of the device used during the tests (see Section 2). The most significant difference is the presence of a larger number of sensors: the first prototype includes an air and humidity sensor and a water temperature sensor. As for the transmission modality, all nodes adopt the same parameters presented in Table 1, including the SF fixed at 12 in order to achieve the maximum possible range. Note that, since SF is set to 12 for each node, it is not necessary to communicate this parameter to adjacent nodes. The nodes are able to receive and transmit and, hence, to enable Peer-to-Peer communications. More specifically, the proposed multi-hop procedure is implemented by creating an ad-hoc firmware deployed on the microcontroller of each node. In order to optimize the overall system power consumption, a duty cycling policy has been adopted. To elaborate, the Sensor Node is _active_ only for the amount of time required for sensing the environment and for data communication.