## 3 Related Work  
WSN technologies have been studied in many literature works to address the requirements of monitoring systems. These also include non-LoRa technologies such as Zigbee and Wi-Fi, and they cover applications such as pipeline monitoring systems, marine and underwater monitoring systems, and tunnel monitoring. Some are star networks, such as in [18], and some are related to linear networks, like [19; 20; 21; 22]. These papers apply multi-hop communication to provide a reliable linear WSN. However, these systems face two challenges: high energy consumption and limited network coverage. The work in [22] studied a monitoring system based on LoRaWAN technology. The evaluation showed that LoRaWAN could provide promising results in terms of network coverage in monitoring applications. The system had efficient results in leak detection. Another development of LoRaWAN in monitoring applications was presented in [23] for the deployment of a cost-effective monitoring system. The system had efficient results in  
Figure 1: LoRaWAN network architecture [17]. terms of energy and coverage; however, there was no estimation of the network throughput. In [24], the authors studied a LoRaWAN system targeting enhanced network reliability and avoiding packet collisions by using clusters; however, there were no relevant energy consumption estimations or delay evaluations. In [25], the authors present an oil pipeline monitoring system using LoRa technology and show the limitations of the system in terms of network coverage. In [26], the authors applied the multi-hop LoRa network in smart city applications to extend the required coverage area. They concluded that multi-hop LoRa achieves a better result in energy consumption compared to LoRa single-hop networks, with some concerns about network scalability. Another comparison between single- and multi-hop LoRa was made in [27]. The authors used the multi-hop LoRa in monitoring systems and applied a mesh topology. The results showed an enhancement in the packet delivery ratio; however, they highlighted some limitations in terms of end-end delay and energy consumption. The work in [28] proposed a general multi-hop protocol based on the LoRaWAN network. In the evaluation, the authors compared the single-hop and multi-hop scenarios in terms of energy consumption and showed that the multi-hop protocol achieved better results. In [29], the authors proposed a linear multi-hop infrastructure to monitor gas pipelines. The aim was to use multi-hop LoRa to achieve wide network coverage for long pipelines. The results showed improvement in the duty cycle. There was no throughput estimation. Furthermore, the work presented in [30] proposed a linear multi-hop LoRa network that enhanced the coverage range in monitoring systems. The authors also presented a new sensor synchronization solution that was evaluated in terms of achieved throughput. However, energy consumption was an issue. Additionally, the authors in [31] provided various network architectures (scenarios) to monitor a gas pipeline. Their objective was to find the best scenario that decreased network failures. The energy consumption and the throughput were not considered. Another work [32] proposed a LoRaWAN network, and the authors analyzed the system throughput using different multi-hop scenarios. Additionally, the authors of [33] presented an underground monitoring system based on multi-hop LoRaWAN technology to solve the problem of increasing the distance between the gateway and sensors, which enhanced the packet delivery for sensors, highlighting the issue of packet collisions. Another work [34] proposed a solution for extending the coverage limits of LoRa gateways. They presented a linear multi-hop uplink extension for the LoRaWAN network and a mechanism to solve the issue of packet collisions, identifying relevant throughput limitations. The system was generalized, and no application requirements were considered. In [35], the authors suggested a scalable multi-hop mechanism based on a linear LoRaWAN network.