## 2 Related Work  
Integrating mesh topologies into LoRa wireless technology is an active area of research that both academia and the LoRa Alliance are pursuing. A recent LoRaWAN specification established the guidelines for incorporating relay devices into typical LoRaWAN star topology networks to extend coverage, but it is limited to serving 16 devices per relay node, and the sole role of the relay node is to forward frames, which does not provide enough flexibility for certain type of scenarios [24]. Conversely, most mesh proposals in the literature developed for LoRa do not comply with the LoRaWAN approved specifications. [PERSON] et al. presented a mesh proposal for LoRa networks in [25]. The authors of this work carried out tests on a university campus to provide LoRa coverage in an area of 480,000 m\({}^{2}\) with 19 devices. These tests included in-building and outdoor deployments. The results showed a packet delivery ratio (PDR) of 58.7% for the traditional star topology and 88.49% for the proposed mesh system. Moreover, they stated that signal-to-noise ratio (SNR) values higher than \(-\)5 dB and received signal strength indicator (RSSI) values higher than \(-\)110 dBm are necessary to achieve PDR results above 90%. Applying mesh LoRa solutions to UAVs (unmanned aerial vehicles) has also been considered, specifically for the case of data communication in environmental monitoring systems. The medium access control (MAC) protocol proposed by [PERSON] et al. was designed based on a slotted ALOHA [26]. Their proposed mesh system considered the deployment of LoRa relay devices that enabled communication between sensor nodes and the gateway. Tests were performed both in laboratory and outdoor settings. The results returned delays lower than 6 s for 1-hop transmissions, line-of-sight distances of 10 km, and data rates of 293 bit/s. Multi-hop solutions have been addressed in other works as a first step toward mesh networks. The authors in [20] studied multi-hop LoRa network topologies. Metrics such as coverage, packet reception ratio (PRR), and energy efficiency were evaluated for different configurations of transmission power or spreading factor (SF). Tests were conducted using outdoor end devices. The results revealed that multi-hop topologies outperformed star topologies with 50% energy savings and 35% increased coverage for a 90% PRR. Among multi-hop proposals, introducing devices to relay information to the next node is a popular approach. [PERSON] et al. presented a LoRa-based meshed multi-hop network intended for communications in underground environments such as sewers [27]. The proposed protocol included a new LoRa frame format for synchronous connections and the timeslot allocation method. The proposed system comprised sensor nodes, repeater nodes, and gateways. Tests were performed in two cities in Switzerland using 17 devices. The results showed better PDR performance for the mesh deployment than standard LoRaWAN. [PERSON] et al. developed a cluster-based protocol for LoRa multi-hop communications [28]. It included cluster-head nodes able to operate with both LoRa and WiFi, as well as aggregator nodes operating as relay nodes. The message format and message exchange for all the phases of the protocol were provided as well. Proof of concept tests were performed to validate the proposal. The results obtained on bandwidth consumption indicated that the proposed protocol complied with the most restrictive LoRa configurations. Furthermore, higher PDR values were attained for packet transmission delays of 500 ms.  
With the advance in mesh solutions for LoRa, proposals and implementations of routing protocols for mesh networks began to arise. The routing protocol proposed by [PERSON] et al. was intended for LoRa mesh hierarchical networks with a focus on energy efficiency [29]. This protocol used contention-free concurrent transmission and minimized packet collisions. Simulations and experimental tests were undertaken as proof of concept.