# A Review of Flying Ad Hoc Networks: Key Characteristics, Applications, and Wireless Technologies
## 3 Main Characteristics of FANETs
### Changing network topology  
**4. Main Applications of FANETs**  
Three main applications of FANETs can be distinguished as follows [40]:  
* Multi-UAV cooperation: Figure 4, box \(A\) shows the following applications, which can be categorized as multi-UAV cooperation:  
Figure 3: FANET characteristics, including localization, power consumption, frequency band, radio propagation model, changing network topology, node mobility, and node density.  
* _Target detection_: Target detection technologies such as thermal and vision cameras can be employed in UAVs to detect objects and persons [43; 75].
* _Tracking and monitoring in disaster situations_: UAVs can help to assess the direction in which a flood is moving, then predict what buildings are exposed to damage. Similarly, they can be used for rescue operations in the aftermath of earthquakes, identifying collapsed population-dense buildings such as hospitals and schools so that these areas are given a higher priority in rescue operations [76; 77].
* _Emergency situations_: UAVs are used in the construction industry to check safety and to monitor the progress of construction and buildings. UAVs can be used to provide temporary wireless coverage in cellular networks during emergencies when the ground base stations are out of service, as well as in many other emergency scenarios [33; 54].
* UAV-to-Ground tasks: Figure 4, box \(B\) shows the following applications for UAV-to-ground cooperation:
* _Public and civilian applications_: UAVs have been widely used for public and civilian domain applications, especially in the form of small quadcopters, as their cost effectiveness and flexibility provide advantages over ground-based infrastructure [78].
* _Search and rescue missions_: UAVs play a vital role in search and rescue missions (SAR). FANETs are considered an immense advantage in guaranteeing public safety, performing SAR missions, and managing man-made or natural disasters such as floods, earthquakes, forest fires, tsunamis, terrorist attacks, and checking the safety of critical infrastructure such as power and water utilities. It is important to provide communications coverage in such situations. In situations when public communications networks are disrupted, UAVs can provide timely disaster warnings and help to speed up rescue and recovery operations. UAVs can carry medical equipment to inaccessible regions. They can make SAR operation much faster in situations such as avalanches, wildfires, searching for missing persons, and more.
* UAV-to-VANET collaborations between UAVs and vehicles: As shown in Figure 4, box \(C\), the following applications involve cooperation between UAVs and vehicles:
* _Roadway traffic monitoring_: FANETs can be employed instead of intensive labour and complex observational infrastructure to carry out road traffic monitoring. In roadway traffic monitoring, UAVs are able to detect traffic crashes and then report these incidents easily. Using UAVs is much faster than using the incident commander's vehicle. In addition, UAVs can be used to provide road safety by capturing real-time videos from various security scenarios and situations in road networks [79].
* _Data packet delivery_: Data delivery to mobile ad hoc nodes is a challenging task, as it is difficult to find a reliable forwarding path to ensure that data is delivered from one user to another. In this respect, UAVs are widely used as airborne communication relays to deliver data collected by ground devices to distant control centres. In other words, UAVs deliver packet data based on the load-carry-and-delivery (LCAD) paradigm, in which data is loaded from the source node and forwarded to the destination node utilizing multiple UAVs [80; 81].
* _Route guidance_: In VANETs, the high mobility of vehicles leads to inadequate routing. In UAV-assisted VANETs, vehicles and UAVs transmit data to each other using multi-hop relays. UAVs are used to provide route guidance and routing improvement in VANETs [82; 83].