# Adaptive Emergency Call Service for Disaster Management
## 2 Related Works
### Wireless Network Recovery  
Multiple works of the literature [5; 16; 17] address the resilience and self-adaptation of the mobile networks to face a disaster affecting the network infrastructure using various mechanisms. In Table 1, the research works on recovery solutions for wireless networks are presented. The extended architecture-based approaches complicate the 3 GPP compatibility in communications and add extra infrastructure costs. In this case, external or movable physical units, such as satellite [18] or unmanned air vehicles (UAV) [19; 20; 21; 22], are deployed to rapidly work as a stand-in for damaged network facilities. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Related Work** & & & & \\ \hline UAV-Assisted Attack Prevention, Detection, and Recovery of 5G Networks [19] & x & & & x \\ \hline Post-Disaster 4G/5G Network Rehabilitation Using Drones: Solving Battery and Backhaul Issues [20] & x & & x \\ \hline Integration of satellite and LTE for disaster recovery [18] & x & & x \\ \hline UAV-Empowered Disaster-Resilient Edge Architecture for Delay-Sensitive Communication [21] & x & & x \\ \hline On the Disaster Resiliency within the Context of 5G Networks: The RECODIS Experience [16] & x & x \\ \hline Enabling Disaster Resilient 4G Mobile Communication Networks [23] & x & x \\ \hline Terrestrial Trunked Radio-Tetra: A Global Security Tool [24] & x & x \\ \hline Towards Failure Resiliency in 5G: Service Shifting [25] & x & x \\ \hline Ad-hoc network recovery after severe disaster [26] & x & x \\ \hline A mobile ad-hoc network multi-path routing protocol based on biological attractor selection for disaster recovery communication [27] & x & x \\ \hline D2D Multihop Energy-Efficient Routing and OFDMA Resource Allocation in 5G Networks [28] & x & x \\ \hline Assisted Routing Algorithm for D2D Communication in 5G Wireless Networks [29] & x & x \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Existing works in the literature on wireless network recovery. Moreover, resilient architecture-based approaches are less disruptive to the 3 GPP specifications. In [23], the authors proposed to relax the dependencies between UEs, gNBs, and the core network. The objective is to provide more resilience against link disruptions by using the virtualization/redundancy of the links and functionalities. Although this approach is efficient for localized perturbations, it remains inefficient when the disaster impact is over a large geographical area. The application-based approaches try to manage the reliability and robustness issues on the service layer [24, 25]. The application has to detect the communication failure and has to adapt the transfer mode accordingly (use of other wireless technology, other coding schemes, data substitution, etc.). The resilient protocol-based approach is widely discussed for ad-hoc networks [26, 27]. However, those protocols are incompatible with 5G network specifications. Some resilient-based protocols compatible with the 3 GPP standard are proposed such as [28, 29]. Nevertheless, most of these protocols can not be used in an out-of-coverage situation when the disaster affects the network infrastructure. Even if dealing with disaster situations is well studied in ad-hoc network literature [30, 31, 32], the projection of those solutions over 4G/5G cellular standards is rarely studied and remains difficult. Furthermore, the user equipment (network nodes) is not owned by the system itself, making the protocol possibilities more regulated and constrained than in private/community networks such as MANET and VANET systems [33, 34]. Meanwhile, the FINDER protocol in [10] represents one of the rare works on the massive use of D2D mechanisms to overcome large disaster situations. In FINDER, emergency calls are forwarded to working gNBs by clustering and organizing the out-of-coverage mobile devices. There is a cluster head (CH) in each cluster that is selected by the members of the cluster. The CH receives emergency calls transmitted by mobile nodes within its cluster.