# Efficient Security Scheme for Disaster Surveillance UAV Communication Networks
## 7 Performance Evaluation
### Communication Complexity  
To guarantee the accuracy of rescue operations, information about current status of the disaster area should be sent periodically to \(CS\). Thus, the communication duty for each monitoring drone every reading round is sending two messages to the two cluster heads while each head sends the concatenated message to \(CS\) via relays; this communication burden is affordable for the drones. According to the relays, they store the received messages and then forward them all as one packet to the \(CS\) when the relay enters the coverage range of \(CS\). In other works, relays' communication load is considered one message too. Because the proposed scheme guarantees the integrity and availability of the information by several ways, the probability for \(CS\) to ask for specific information retransmission due to malfunction or malicious attacks is reduced. The communication overhead, the number of transmitted messages, for each monitoring drone equals two messages and for the whole mission time, i.e., 15 min, equals 1800 messages (if the drone sends its reading every second). While the relays receive and store certain number of messages during the journey but forward them as a one message when reaching to \(CS\), the relay is sending one message. However, in the join/leave process, the connecting drone only sends one message to the head to join the group. In conclusion, the total communication load for drones is limited and trivial overhead. Table 3 demonstrates the communication overhead for each monitoring drone per round and for the whole flying time (15 min) in the proposed scheme. Figure 7 shows the communication overhead for the operation of collecting the area information per reading round; it presents the communication load for readings transmission from the monitoring drones to the cluster heads in each group in the whole subarea. The number of transmitted messages by each monitoring drone in the reading round is fixed so that the communication delay of the group increases linearly as the number of the involved drones increases. Similarly, the communication overhead for the subarea increases as the number of the groups and number of participated drones increase. This leads to the fact that the more important subareas have higher communication burden, but the communication overhead is still affordable by the UAV network. According to cluster heads, their communication loads include the overhead of forwarding the group aggregated readings to the chosen relays, i.e., in addition to the communication overhead of their monitoring mission. The number of relays is changing according to the drones' batteries conditions; \begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{**Drone Type**} & \multicolumn{2}{c}{**Communication Overhead**} \\ \cline{2-3}  & **Per Round** & **Total** \\ \hline Monitoring & 2 & 1800 \\ \hline Relay & 0 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Monitoring drones communication overhead. Figure 6: Energy consumption. this number seems unpredictably and randomly changing for the cluster heads. Consequently, the total number of forwarded messages by clusters is fluctuated according to the current number of relays. Figure 8 shows the real-time variation in the cluster head's communication overhead due to forwarding the readings packages to relays. The figure presents three different cases: when the maximum number of drones in the group can reach 5, 10, and 20 drones. Notice that the number of forwarding packages fluctuates as the number of relays changes but within a range, i.e., less than the maximum number of drones in the group. For instance, when the group has 20 drones, the number of drones converted to relays is always changing in the range zero to less than 20. In addition, the cluster head selects number of relays (not all of the returning drones) to forward the reading package. Moreover, the drone plays the cluster head role for a limited time period; it may be not working as a cluster head at all for the whole flying time.