# Opportunistic Multi-Technology Cooperative Scheme and UAV Relaying for Network Disaster Recovery  
[PERSON]  
1 Inria Lille--Nord Europe, 40 Avenue Halley, 59650 Villeneuve d'Ascq, France; [EMAIL_ADDRESS]  
2  
[PERSON]  
1 Inria Lille--Nord Europe, 40 Avenue Halley, 59650 Villeneuve d'Ascq, France; [EMAIL_ADDRESS]  
Footnoteand ubiquitous-nature. On the other hand, the rescue teams must be able to timely make use of such information and lead rescue operations efficiently.  
In this respect, UAV (Unmanned Aerial Vehicles) such as drones, have been employed to provide an on-demand communication infrastructure for disaster scenarios [1; 2; 3]. Drones are particularly suitable for such situations as they can quickly and easily cover affected areas. However, using drones as a communication infrastructure for disaster recovery raises two key challenges. First, they should be able to reliably discover survivors as soon as possible. This also means that energy-efficient communication protocols should be in place to extend the time devices owned by survivors can be used for emergency response. Second, they should cover the affected area in the shortest possible time, and many survivors as possible.  
Data dissemination under missing or damaged communication infrastructure has received increasing attention in the last few years [4; 5; 6; 7]. However, most of these solutions are based upon a single communication interface (e.g., WiFi), and assume a certain level of cooperation and organization of rescue teams in the territory, thereby complementing (instead of replacing) the existing communication services. Exploring and extending the coverage of wireless communications with UAVs has also been widely investigated, especially in situations where human lives would be endangered and people cannot be physically reached [1; 2; 3]. However, most of recent solutions [8; 9] solely address placement and optimization of UAVs to offer wireless communication in specific areas, and do not consider the communication aspects related to the end devices, for instance, in terms of energy efficiency.  
This work specifically addresses these issues by leveraging the ubiquitous presence of mobile devices in urban scenarios to assist search and rescue activities following a disaster. Specifically, it proposes a collaborative protocol that opportunistically organizes mobile devices in multiple tiers by targeting a fair energy consumption in the whole network. In doing so, it spontaneously relies on the multiple radio interfaces in off-the-shelf personal mobile devices for energy-efficient operations. Moreover, it introduces a complementary data collection scheme that employs drones to visit mobile devices and collect their data in a short time. The main contributions of this work are the following.  
* It formally characterizes the creation of a multi-tier communication infrastructure of mobile devices with multiple radio interfaces. It then derives a heuristic for clustering nodes based on their local connectivity and available energy.
* It evaluates the performance of smartphones in terms of network interfaces (based on energy consumption and transmission range) and clock synchronization.
* It introduces a scheme for drone-based data collection that minimizes the total flying path, while still ensuring a sufficient time to collect data. In particular, it derives the locations that a hovering drone needs to reach and stop at to collect data from mobile devices based on a multi-tier network structure.  
Extensive simulations in realistic settings demonstrate that the proposed solution balances the energy consumption in the network by means of efficient drone routes, thereby effectively assisting search and rescue operations.