# Opportunistic Multi-Technology Cooperative Scheme and UAV Relaying for Network Disaster Recovery
## 3 Multi-Technology Cooperative Communication and Drone Data Relaying
### Energy Consumption and Transmission Range  
COPE proposes a multi-technology cooperative communication for a fair energy consumption in the whole network. Experiments were conducted to measure the energy consumption based on a non-cooperative and cooperative network topologies as follows:  
1. a non-cooperative communication scheme considering only one node that operates individually; i.e., nodes switch on their network interfaces (Bluetooth and WiFi direct) for communication  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Smartphone Model** & **Wiko Tommy 2** \\ \hline OS & Android 7.1 (Nougat) \\ Battery & Li-Po 2500 mAh 9.5 Wh \\ Bluetooth & 4.1, A2 DP, LE \\ WiFi & WiFi Direct \\ \hline \hline \end{tabular}
\end{table}
Table 1: Smartphones main specifications.  
* a cooperative communication scheme (i.e., COPE) considering two and three nodes respectively; i.e., nodes form groups based on the Bluetooth, then, periodically only one node turn on its WiFi interface at the same time to communicate For measurements, only COPE application was running on smartphones with the screen turned off.  
Figure 2 illustrates the energy consumption over five minutes from the WiFi and Bluetooth perspective considering the three network topologies. Results show that when a node operates individually, it consumes more energy than in the other topologies where nodes are cooperating. Moreover, as we increase the number of nodes within the group, the energy consumption is reduced since nodes will be in a sleep mode for a longer period from the WiFi perspective. Therefore, a cooperative scheme can help to reduce the energy consumption and thus to keep mobile devices alive for a longer time. We would like to emphasize that these experiments validate that, in addition, Bluetooth consumes less energy than WiFi in the context of applications requiring an exchange of small data (e.g., short text message). In the context of COPE that only needs to send short SOS messages, this confirms our assumptions.  
We have carried out experiments to test the transmission ranges of Bluetooth and WiFi-Direct. Testing the quality of the link and the transmission speed are not in the scope of this work (See [22] for a related study). Indeed, we consider the necessity of exchanging short text messages that can be useful for alerting or asking for assistance. Thus, in our testing scenarios, we simply try to exchange some short messages of few bytes between smartphones and we keep increasing the distance between mobile nodes until the link interruption. We have carried out various testing scenarios considering: windy and humid weathers; calm and dry weathers; outdoor line of sight (see yellow lines on Figure 3); indoor with obstacles (1 to 2 walls); between two buildings with a distance of about 80 m (see red line on Figure 3).  
Table 2 presents the transmission range of the Bluetooth and Wi-Fi Direct for outdoor and indoor scenarios. These results show the importance of the new version of Bluetooth offering an important transmission range comparing to the previous versions. Several research works consider the transmission range of Bluetooth of around 10 m while the new version of Bluetooth (Bluetooth Low Energy BLE) offers more important transmission ranges compared to what is expected even in theory. Moreover, experiments validate the assumptions considered in COPE solution that WiFi offers a higher transmission range than Bluetooth.  
Figure 2: Energy consumption.