# Energy-Efficient Opportunistic Routing Algorithm for Post-Disaster Mine Internet of Things Networks
If there are too many nodes participating in packet forwarding, high communication energy consumption will be generated in the network, and nodes will fail quickly due to energy depletion, thereby aggravating the intermittent connectivity of the post-disaster MIoT. Conversely, if there are few nodes for packet forwarding, the packet delivery success rate of the post-disaster MIoT cannot be guaranteed. Therefore, the size of the candidate forwarding set becomes a crucial factor affecting the network performance. Second, the MIoT network data transmission in affected regions tends to be directional, and critical network nodes close to the sink will undertake more transmission tasks, resulting in the routing hotspot problem, which severely reduces the energy utilization of surviving nodes. Third, the harsh environment in post-disaster underground mines makes surviving nodes prone to physical damage, causing unstable network topology and void routing, which severely degrade the reliability of transmission links. To the best of our knowledge, there are fewer studies on OR methods in the post-disaster Mine Internet of Things (MIoT). Therefore, the focus of our work is to address the aforementioned problems of opportunistic routing in the post-disaster MIoT. In this paper, we propose a Directional-area-forwarding-based Energy-efficient Opportunistic Routing (DEOR) algorithm to improve the reliability and robustness of data transmission in post-disaster MIoT networks. The main contributions and innovations of this paper are summarized as follows. 1. In order to restore post-disaster data transmission of MIoT in the planar accident area rescue scenarios, such as a fully mechanized coal face, a post-disaster flat network architecture of MIoT based on the multi-hop routing of surviving nodes is established, which consists of a sink node and multiple sensor nodes. This network architecture achieves the purpose of comprehensive perception and effective transmission of environmental information in the planar accident mine after disasters;2. We propose a directional-area-forwarding-based candidate forwarding set construction strategy. In the network initialization phase, according to the deployment density and communication radius of nodes in the accident roadway, a forwarding zone (FZ) is designed for each node to route packets toward the sink. Then, the candidate forwarding set (CFS) is constructed by the nodes within the FZ that satisfy the energy constraint and the neighboring node degree constraint. By restricting the number of duplicated packets in the network, DEOR improves the energy utilization of the surviving nodes;
3. We propose a relay node selection method based on routing quality evaluation. In the data transmission phase, we take multiple attributes of the nodes into account, such as direction angle, transmission distance, and residual energy. Next, nodes in the CFS are prioritized based on the routing quality, and the forwarding node with the highest priority is selected as the relay node to forward packets. Other nodes in the CFS discard packets after listening for a successful transmission message. By utilizing the collaboration between forwarders, DEOR addresses the hotspot problem and balances the traffic load between nodes in the post-disaster network;
4. We design a recovery mechanism for void nodes. When packets encounter the routing void during forwarding, a recovery mechanism is triggered. By employing the modified routing quality evaluation function, packets can bypass the void routing region and select available relay nodes to continue forwarding. DEOR overcomes the void routing node problem and improves the robustness of the whole post-disaster network. Extensive simulation tests proved that the proposed DEOR algorithm obviously improves the performance of post-disaster MIoT data transmission in a planar accident mine.