FANET (Flying Ad-Hoc Network) has emerged as an alternative access technology for regions that have no fixed infrastructure or are hard to reach. It is a group of UAVs communicating with each other with no need to access point, but at least one of them must be connected to GCS (Ground Control Station) or satellite. FANET differs from existing Ad-Hoc networks such as MANET (Mobile Ad-Hoc Network) and VANET (Vehicle Ad-Hoc Network) in terms of conception and design (connectivity, quality of services, sensor types, node movement features, data delivery, service discovery, etc.).
Over the past few years, a large number of researchers investigate the conception of systems that use multiple UAVs to cooperatively conduct civil or military missions, with minimal human intervention. From a network security viewpoint, the existing ad-hoc security solutions can be ineffective or cannot be operated due to the features of FANET .
FANET Application Scenarios[Redakto | Redakto nëpërmjet kodit]
FANET comes with different application scenarios.
Extending the scalability of multi-UAV operations[Redakto | Redakto nëpërmjet kodit]
If a multi-UAV communication network is established fully based on an infrastructure, such as a satellite or a ground base, the operation area is limited to the communication coverage of the infrastructure. If a UAV cannot communicate with the infrastructure, it cannot operate. On the other hand, FANET is based on the UAV-to-UAV data links instead of UAV-to-infrastructure data links, and it can extend the coverage of the operation. Even if a FANET node cannot establish a communication link with the infrastructure, it can still operate by communicating through the other UAVs. There are several FANET designs developed for extending the scalability of multi-UAV applications. In , a FANET design was proposed for the range extension of multi - UAV systems. It was stated that forming a link chain of UAVs by utilizing multi-hop communication can extend the operation area. It should be noticed that the terrain also affects the communication coverage of the infrastructure. There may be some obstacles on the terrain, such as mountains, walls or buildings, and these obstacles may block the signals of the infrastructures. Especially in urban areas, buildings and constructions block the radio signals between the ground base and UAVs. FANET can also help to operate behind the obstacles, and it can extend the scalability of multi- UAV applications .
Reliable multi-UAV communication[Redakto | Redakto nëpërmjet kodit]
“In most of the cases, multi-UAV systems operate in a highly dynamic environment. The conditions at the beginning of a mission may change during the operation. If there is no opportunity to establish an ad hoc network, all UAVs must be connected to an infrastructure. However, during the operation, because of the weather condition changes, some of the UAVs may be disconnected. If the multi-UAV system can support FANET architecture, it can maintain the connectivity through the other UAVs. This connectivity feature enhances the reliability of the multi-UAV systems.
UAV swarms[Redakto | Redakto nëpërmjet kodit]
Swarm behavior of UAVs requires coordinated functions, and UAVs must communicate with each other to achieve the coordination. However, because of the limited payloads of small UAVs, it may not be possible to carry heavy UAV-to-infrastructure communication hardware. FANET, which needs relatively lighter and cheaper hardware, can be used to establish a network between small UAVs. By the help of the FANET architectures, swarm UAVs can prevent themselves from collisions, and the coordination between UAVs can be realized to complete the mission successfully. Quaritsch et al. have developed another FANET based UAV swarm application for disaster management. During a disaster situation, rescue teams cannot rely on fixed infrastructures. The aim of the project is to provide quick and accurate information from the affected area.
Mobility model and The Existing Ad-hoc Networks[Redakto | Redakto nëpërmjet kodit]
FANET is a new form of MANET in which the nodes are UAVs. According to this definition, single- UAV systems cannot form a FANET, which is valid only for multi-UAV systems. Not all multi-UAV systems form a FANET. The UAV communication must be realized by the help of an ad hoc network between UAVs. Therefore, if the communication between UAVs fully relies on UAV-to-infrastructure links, it cannot be classified as a FANET. UAV ad hoc network  is closely related to FANETs. There is no significant difference between the existing UAV ad hoc network researches and the FANET definition. However, FANET term immediately reminds that it is a specialized form of MANET and VANET. While MANET nodes move on a certain terrain, VANET nodes move on the highways, and FANET nodes fly in the sky. MANETs generally implement the random waypoint mobility model, in which the direction and the speed of the nodes are chosen randomly. VANET nodes are restricted to move on highways or roads. Therefore, VANET mobility models are highly predictable.
In some multi-UAV applications, global path plans are preferred. In this case, UAVs move on a predetermined path, and the mobility model is regular. In autonomous multi-UAV systems, the flight plan is not predetermined. Even if a multi-UAV system uses predefined flight plans, because of the environmental changes or mission updates, the flight plan may be recalculated. In addition to the flight plan changes, the fast and sharp UAV movements and different UAV formations directly affect the mobility model of multi-UAV systems. In order to address this issue, FANET mobility models are proposed. In, Semi-Random Circular Movement (SRCM) mobility model is presented, and the approximate node distribution function is derived within a two dimensional disk region. In, two new mobility models are proposed for multi-UAV systems. In random UAV movement model, UAVs move independently. Each UAV decides on its movement direction, according to a predefined Markov process. In the second model, the UAVs maintain a pheromone map, and the pheromones guide their movements. Each UAV marks the areas that it scans on the map, and shares the pheromone map with broadcasting. In order to maximize the coverage, UAVs prefer the movement through the areas with low pheromone smell. It was shown that the use of a typical MANET mobility model may result in undesirable path plans for cooperative UAV applications. It was also observed that the random model is remarkably simple, but it leads to ordinary results. However, the pheromone based model has very reliable scanning properties.
FANET Design Considerations[Redakto | Redakto nëpërmjet kodit]
The distinguishing features of FANET impose unique design considerations. The most prominent FANET design considerations are: adaptibility, scalability, latency, UAV platform constraints, and bandwidth requirement.
Adaptability[Redakto | Redakto nëpërmjet kodit]
Various FANET parameters can change during the operation of a multi-UAV system. FANET nodes are highly mobile and always change their location. Because of the operational requirements, the routes of the UAVs may be different, and the distance between UAVs cannot be constant. Another issue that must be considered is the UAV failures. Consequent to a technical problem or an attack against multi-UAV system, some of the UAVs may fail during the operation. While UAV failures decrease the number of UAVs, UAV injections may be required to maintain the multi-UAV system operation. UAV failures and UAV injections change the FANET parameters .
Environmental conditions can also affect FANET. If the weather changes unexpectedly, FANET data links may not survive. FANET should be designed so that it should be able to continue to operate in a highly dynamic environment. The mission may also be updated during the multi-UAV system operation. Additional data or new information about the mission may require a flight plan update. For example, while a multi-UAV system is operated for a search and rescue mission; after the arrival of a new intelligence report, the mission may be concentrated on a certain area, and the flight plan update also affects FANET parameters. FANET design should be developed so that it can adjust itself against any changes or failures. FANET physical layer should adapt according to the node density, distance between nodes, and environmental changes. It can scan the parameters and choose the most appropriate physical layer option. The highly dynamic nature of FANET environment also affects network layer protocols. Route maintenance in an ad hoc network is closely related to the topology changes. Thus, the performance of the system depends on the routing protocol in adapting to link changes. Transport layer should also be adapted according to the status of FANET.
Scalability[Redakto | Redakto nëpërmjet kodit]
Collaborative work of UAVs can improve the performance of the system in comparison to a single-UAV system. In fact, this is the main motivation to use multi-UAV based systems. In many applications, the performance enhancement is closely related with the number of UAVs.
For example, the higher number of UAVs can complete a search and rescue operation faster. FANET protocols and algorithms should be designed so that any number of UAVs can operate together with minimal performance degradation.
Latency[Redakto | Redakto nëpërmjet kodit]
Latency is one of the most important design issues for all types of networks, and FANET is not an exception. FANET latency requirement is fully dependent on the application. Especially for real-time FANET applications, such as military monitoring, the data packets must be delivered within a certain delay bound. Another low latency requirement is valid for collision avoidance of multiple UAVs . In, an analysis of one-hop packet delay was conducted for IEEE 802.11 based FANETs. Each node was modeled as M/M/1 queue and the mean packet delay was derived analytically. The numerical results were verified with a simulation analysis. Based on the data collected from the simulation analysis, it was observed that packet delay can be approximated with Gamma distribution. Zhai et al. studied packet delay performance of IEEE 802.11 for traditional wireless LANs, and stated that the MAC layer packet service time can be approximated by an exponentially distributed random variable. It also shows that the packet delay behaviors are different for MANETs and FANETs, and the protocols developed for MANET may not satisfy the latency requirements of FANET. New FANET protocols and algorithms are needed for delay sensitive multi-UAV applications.
UAV platform constraints[Redakto | Redakto nëpërmjet kodit]
FANET communication hardware must be deployed on the UAV platform, and this situation imposes certain constraints. The weight of the hardware is an important issue for the performance of the UAVs. Lighter hardware means lighter payload, and it extends the endurance. Another opportunity that comes with the lighter communication hardware is to deploy additional sensors on the UAV. If the total payload is assumed as constant and the communication hardware is lighter, more advanced sensors and other peripherals can be deployed. Space limitation is another UAV platform related constraints for FANET designs. Especially for mini UAVs, the space limitation is very important for communication hardware that must be fitted into the UAV platform.
Bandwidth requirement[Redakto | Redakto nëpërmjet kodit]
In most of the FANET applications, the aim is to collect data from the environment and to relay the collected data to a ground base. For example, in surveillance, monitoring or rescue operations; the image or video of the target area must be relayed from the UAV to the command control center with a very strict delay bound, and it requires high bandwidth. In addition, by the help of the technological advancements on sensor technologies, it is possible to collect data with very high resolution, and this makes the bandwidth requirement much higher. The collaboration and coordination of multiple UAVs also need additional bandwidth resource.
On the other hand, there are many constraints for the usage of available bandwidth such as:
- Capacity of the communication channel,
- Speed of UAVs,
- Error-prone structure of the wireless links,
- Lack of security with broadcast communication.
A FANET protocol must satisfy the bandwidth capacity requirement so that it can relay very high resolution real-time image or video under several constraints.
FANET Security[Redakto | Redakto nëpërmjet kodit]
Similar to all the wireless networks, securing FANET is a primordial task. It can be said whether an Ad-Hoc network is secure or not according to the main security criteria: availability, integrity, confidentiality, authenticity, nonrepudiation, authorization and anonymity. Due to the specific nature of FANET networks: collaborative characteristics, wireless links, the absence of a fixed infrastructure and the uncontrollable environment, securing such networks is a difficult and challenging work. In 2016, Nils Rodday performed a live hack by exploiting a professional drones vulnerabilities to compromises a system and take control of UAV system . According to, the main security services that an attacker wants to break are authentication, availability, confidentiality and integrity.
The FANET networks are inherently insecure and need effective security schemes that take into consideration the special characteristics of FANET, because these specific features are the principal causes of its vulnerabilities to attacks. The use of wireless link between the transmitter and the receiver can be source to links attacks such as active interfering, passive eavesdropping, data tampering, leaking secret information, message replay, message misuse, denial of service and impersonation. Due to the uncontrolled environment in Ad-Hoc network, attacks can happen from the inside and the outside. For example, once an attacker is in the transmission range of a node, it can send and receive data packets.
Furthermore more UAVs are vulnerable to physical capture. Another problem that arises in FANET is the dynamic topology. It is usually difficult to correctly detect the misbehaving node due to the poor link quality. Also, the cooperation between the UAVs nodes, in path discovery for example, can be a critical source of attacks, because there is no guarantee that a route between two UAVs will be free of mischievous nodes. Finally, the attackers can exploit the limited resources of small UAVs to drain UAV battery power. The security algorithms that will be proposed for FANET must take into account the vulnerabilities mentioned above and the security requirements of this network. FANET have mainly seven security requirements:
- Authentication: this ensures that only legitimate UAVs are al- lowed to participate in the cooperative mission. There are two types of authentication services: Node authentication and Message Authentication.
- Integrity: this includes the accuracy, trust worthiness and consistency of data message over their whole passage through the flying networks.
- Confidentiality: this ensures privacy, i.e. allows the data packets to be accessible only by authorized UAVs.
- Identity anonymity: FANET communication should provide identity anonymity to ensure that the attacker cannot obtain the users real identity from eavesdropped or captured messages.
- Availability: this refers that all services provided by the FANET are always available in any time and any condition.
- Timeliness: update information should be transmitted on time to avoid delays.
- Self-stabilization: FANET communication protocols must have the ability to recover automatically from any attacks without the need of human intervention.
Several security schemes have been applied to Ad-Hoc network to ensure reliability and integrity. These mechanisms include the use of cryptographic algorithms (symmetrical, asymmetrical, hashing, hash chains and authentication techniques), the use of intrusion detection methods and the use of reputation based techniques, for packets exchange. Indeed, these methods can be used in UAVs networks. In  the authors analyze how these different methods perform in FANET networks to secure FANET routing protocols and the different routing message exchanged such as path discovery. A few studies have donated to data protection for UAV networks.
He et al.  focuses on four FANET security requirements, mainly authentication, confidentiality, partial privacy-preservation and resistance to denial of service attacks. To ensure authentication, authors of , introduce a mutual authentication scheme between UAVs and end devices using an identity-based signcryption. A signature is generated to verify whether a drone/end device is a real master/receiver or an imitation. To satisfy the confidentiality requirement, He et al.  employs the hierarchical identity-based broadcast encryption approach in which messages for broadcast are encrypted by a preassigned broadcast key. He et al.  achieves privacy-preservation by pseudonym and cipher text transition mechanism. Finally to resist to denial of service attacks a dynamic control of access numbers and the interval of time for each login is proposed. Authors of  introduced a certificate-based encryption to address authentication and confidentiality issues in Ad-Hoc net- works. A negotiated session key is used and transmitted messages are encrypted with a symmetric key to allow secure end-to-end UAV communications. In  an efficient Certificateless Signcryption Tag Key Encapsulation scheme is designed for FANET networks. Besides authentication and confidentiality, this scheme addresses user revocation. The proposed revocation technique adds a valid time period to the partial private keys that are issued. After the time period expires, new private keys are generated. Therefore, if the UAV is captured, information leakage is limited to the time period during which the private keys were valid.
In , the authors focused on physical layer security in FANET communications. The transmit power control and UAV trajectory are jointly designed to maximize the average secrecy rate. By flying closer to the ground nodes, UAVs establish stronger legitimate links with them. Similarly, mobility is exploited to degrade the channels of the eavesdroppers, by flying farther from them.
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