# Flying Real-Time Network to Coordinate Disaster Relief Activities in Urban Areas +
## 3 Proposed Network System
### Flying Witness Units  
A FWU is an unmanned mobile unit that locally stores information and transfers it to other network nodes (e.g., SAR team members) at the same or other locations. Figure 1 shows an example of an FRTN that supports a first response process, and illustrates the main structure and dynamics of these networks.  
In order to support the message delivery in a FRTN, this proposal considers two kinds of FWUs. The first is mainly used to provide direct contact among the members of an SAR team. In this case, each team counts with a dedicated FWU that follows it and acts as gateway to interact with the FWUs of other teams. These units, named team-centered witness units (TWUs), have a mobility level similar to the teams they follow; typically, this means low mobility. If we increase the abstraction level in the analysis and consider a TWU as the communication device of an SAR team, we can conceive meta-TWUs potentially able to bridge regular TWUs. These meta-TWUs are governed by the same rules and have the same purpose and behavior as the regular TWUs, and therefore this proposal does not differentiate between these two type of TWU.  
Figure 1: Example of an FRTN that includes eight team-centered witness units (TWUs) and two flying rules. Members of search-and-rescue (SAR) teams are depicted by smartphones, the “location” symbols near these devices are the TWUs, and the helicopters represents the flying mules.  
The second type of FWU acts as a flying _mule_ that goes from one location to another, following a path that allows it to link disconnected teams. Therefore, the challenge of providing a communication link between disconnected TWUs can be addressed by using meta-TWUs, rules, or a mixture of the two. The best solution will depend on the distance between the nodes to communicate and the communication range of the technology used to support these information exchanges. The goal is always to minimize the number of witness units (i.e., TWUs or mules) required to cover the work area with a signal quality that allows first responders to count on real-time message delivery. Thus, the FRTN saves energy and increases the time period of communication support.  
In the example shown in Figure 1, the cell phones represent the devices used by members of SAR teams to support their activities. These devices use Wi-Fi links (or any other technology) to communicate with the TWUs, which in turn communicate with the flying mules participating in the FRTN. The mules are represented as helicopters in Figure 1. Thus, the FRTN allows the information exchange among teams and with the IC. An added value of the FRTN is that civilians could also access the network, for instance to ask for help or receive directives from SAR teams near them. This contributes to make the SAR process more expedited and effective.  
We envision the TWUs landing at certain spots, and then flying again following the movements of their corresponding SAR teams. The stops of these units allow extending the time window available for exchanging messages and also saving energy. We also envision that only the FWUs triggering the response process will be remotely controlled, particularly those carrying TWUs to be deployed to support SAR teams. Thereafter, truly autonomous behavior of TWUs and flying mules is the goal.