# Multi-Hop Routing Protocols for Oil Pipeline Leak Detection Systems
## 2 Related Work
### LoRa Multi-Hop  
LoRaWAN technology can address the pipeline system requirements in terms of range and power. LoRaWAN systems have been mainly introduced for single-hop topologies, but in recent years many studies have applied them for multi-hop communication as well. In [40] it is discussed that LoRa multi-hop and mesh solutions require targeted design to address the specific requirements from each use case scenario, highlighting scalability, management, and complexity issues. In [41] the authors studied the various deployment options of LoRa mesh and multi-hop topologies, denoting the use of nodes as intermediate relays and additionally highlighting power consumption and optimum sensor placement tradeoffs. In [42] a multi-hop protocol for LoRa is presented, which also considers an SDN network architecture, which demonstrated acceptable trade-offs among performance and scalability. In [43], the authors suggested the use of multi-hop LoRa in Smart City applications to extend the range and reduce the energy dissipated in each sensor node. The authors compared LoRa single-hop and multi-hop communication, and the results showed that the multi-hop option provides better performance, with some concerns about the achieved scalability. In [44], the authors compared the packet delivery in single-hop and multi-hop LoRa to monitor a large area using mesh topology. This system consumed excessive energy and had many limitations in terms of security and latency. The work in [45] proposed routing protocols to minimize the latency, using LoRa multi-hop hierarchical routing and assuming tree-based topologies. The system increased reliability and provided low latency. However, energy issues are not addressed. Additionally, a new multi-hop LoRa communication was proposed in [46] for a linear network. The system enhanced the packet delivery and delay, but when the network scalability increased, it led to low performance in terms of delay. Additionally, the work did not evaluate the system's energy requirements. In [47], an underground monitoring system was studied considering a linear sensor topology. The authors considered a multi-hop LoRa network, consisting of various sensors for measuring water and air indicators and developed an energy cost per sensor.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Protocol** & **Intra/inter Cluster** & **Advantage** & **Disadvantage** \\ \hline Chain-based 1 & Multi-hop/Single-hop & Low delay & Unbalanced CH energy \\ Chain-based 2 & Multi-hop/multi-hop & Low delay & Unbalanced energy \\ RFC+ & Multi-hop/multi-hop & Reduce the CH consumption energy & OverheadNot applicable \\ Multi-Hop LEACH & Single-hop/multi-hop & Scalability & Increase network traffic \\ MH-LEACH & Single-hop/multi-hop & Reduce the transmission energy & Increase network traffic \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of Hierarchical Multi-Hop Routing Protocols.  
Using multi-hop extends the LoRa network coverage and provides reliability. However, some constraints must be considered to achieve energy efficiency and low overhead routing. The proposed networking protocol assumes LoRa multi-hop links serving a linear topology of deployed sensors over the pipeline, considering the tradeoffs presented in the related state of the art research. The system is described in the next section.