# A Location-Aware Waypoint-Based Routing Protocol for Airborne DTNs in Search and Rescue Scenarios
## 1 Introduction  
_Unmanned Aerial Vehicles_ (UAVs) have frequently been coupled with the _Delay Tolerant Network_ (DTN) paradigm, supporting communication and service-delivery in scenarios with intermittent connectivity. In this context, the use of UAVs equipped with various technologies (GPS, cameras, sensors, etc.) has gained a lot attention in contexts, such as monitoring, surveillance and reconnaissance [1]. Indeed, a UAV's ability to easily and quickly reach a point of interest makes them an excellent solution for diverse tasks.  
In particular, the use of a swarm of UAVs to deploy a mobile ad-hoc network makes them suitable for diverse application scenarios, like disaster events, search and rescue operations, and urban monitoring, since an infrastructure-based network may be missing or damaged, being unable to work [2]. Particularly interesting are search and rescue scenarios, where the rescue team may use a swarm of UAVs to independently check the ground area of interest in order to find possible targets, following certain route paths.  
The DTN paradigm is best suited for this type of scenario due to its inherent tolerance to intermittent connectivity, providing buffering and carrying data [3]. DTNs use the store-and-forward policy, where each node holds the entire message or chunks of it (bundle) to forward it to any other node at a later stage. However, many aspects in DTNs are still an open issue, like routing. Several routing protocols have been proposed to maximize the message delivery chances, increasing message replication or relying on nodes behavior prediction. Other routing techniques rely on diverse information to correctly forward the messages among the nodes in the network. Some of these are called _context-aware_ protocols, since they use information about the network to take forwarding decisions, like the nodes' location [4].  
The objective of this work is to propose and analyze a routing solution for DTNs that takes into account geographic information of the nodes and, in particular, waypoints' location. When we consider a Flying Ad-hoc Network (FANET) application, it is very common that UAVs already have a planned movement path, or that, at least, we have known target coordinates to be reached. The UAVs, through hello messages, could communicate their scheduled plan. Thanks to this information, it is possible to devise a routing protocol based on reasonable assumptions and predictions of node encounters, in order to calculate the Time To Intercept (TTI) of a certain location, which could be the base station. In essence, each node can select the best available carrier to send a message to the destination, according to the waypoints' location.  
The remainder of this paper is organized as follows. In Section 2 we discuss general background information combining FANETs and DTNs, whereas Section 3 overviews the related work. Section 4 presents the description of our protocol. In Section 5, we show the performance evaluation of our protocol, compared with several classic DTN routing protocols. Finally, conclusions are drawn in Section 6.