Kuldeep Singh, Anil Kumar Verma. Thapar University, India. INTRODUCTION. In case of calamitous event, when traditional communication methods are out of ...
Flying Adhoc Networks: Concept and Challenges Kuldeep Singh, Anil Kumar Verma Thapar University, India
INTRODUCTION In case of calamitous event, when traditional communication methods are out of service or simply not available, in those situations mobile adhoc networks (MANETs) plays an important role to established communication. MANETs employ grounded mobile nodes which are capable to collect information with the help of sensor, camera and other devices. Nodes in MANETs communicate with each other through wireless communication without use of existing infrastructure. The data collected by nodes in MANETs is transmitted to base station using multi-hop path. These networks are economical and can be formed in quickly whenever required as they do not required existing infrastructure. MANETs have several applications areas such as natural disaster, sensor networks etc. But there are some extreme situations (such as flooding, battle field and rescue operations etc.) where MANETs cannot be deploy. In those situations, flying ad-hoc networks (FANETs) can plays vital role to established communication. FANET is a sub class of MANETs and made up of a swarm of small flying vehicles enable with camera, sensor and GPS system. Swarms of UAVs arrange themselves to communicate in large operational area using wireless network without any centralized device. They communicate with each other locally, with base station and also interact with their environment to get information [4]. FANETs use different types of UAVs based on the various application areas. FANETs employ unmanned aerial vehicle (UAVs), UAV is an aircraft which fly without pilot. UAV can manage itself and fly based on preprogrammed flight plans or can be operated using complex dynamic automation systems which are versatile and flexible in implementation [4]. FANETs use multi-UAVs to perform operations because of limitations of single UAV system such as limited surveillance capability, scalability and flexibility. Multi-UAV system has various advantages over single UAVs such as [1]:
With more number of UAVs, tasks can be parallelized which in turn reduce the completion time of mission. This kind of behavior is very useful for search and rescue applications. In case of single UAV system, whole mission collapse if UAV fails. In multi-UAV systems, nodes can distribute tasks among themselves. Fault tolerance of network increases with multiUAVs. In multi-UAV environment, heterogeneous UAVs can form a network. It is possible to use capabilities of other UAVs as and when required for task completion. So multi-UAV systems are very advantageous for critical applications.
FANET Applications Due to various advantages and wide range of applications areas FANETs are getting attentions of research community around the globe. Various applications of FANETs are explained below:
Military Services: FANET are very useful in military services. Setting up proper communication system is very difficult in military areas. So FANETs are used for information exchange among soldiers, military headquarters. Security Purpose: FANET is capable of receiving information quickly. It can be used to collect information for the security purpose of a delegate visiting to a place where no network infrastructure exists. Calamity Administration: FANET is useful when the existing communication system is damaged due to natural disaster like floods, earthquake, firing etc. Gathering and sending information at such areas becomes difficult is such situation. FANET provides the necessary communication. Search and Rescue Operations :FANET can be used provide a better way to do search and rescue operations such as rescue operation of hostages [1]. Some times in extreme situations, cellular networks get damaged. FANETs provide better rescue services in such conditions by sending periodic updates to other locations.
Figure: FANET Applications
In Sensor Networks: Different sensor devices can be used to collect data to do daily functions like weather forecasting, terrestrial movement tracking etc. FANETs can approach to any remote location without difficulties. Location Aware Services: FANETs can be used in many services [1] like forwarding calls to any location, travel guide for passengers, identify information regarding specific location. City Architecture Planning: FANETs are designed to focus emergency services and military applications but FANETs can be used in the development of a city. FANETs can be used to develop city architecture. UAVs can help to plan and manage architectures of roads and buildings in a city based on its geographical location. Law Enforcement: UAVs capabilities can be utilize for law and order of a city. FANETs can provides surveillance facilities on the roads and the streets of a city in situations of riots and curfew, FANETs can collect video recordings and images to support police or soldiers to control the situation. Later images and videos can be used as evidence in the court against the accused.
BACKGROUND The term FANETs is first introduced by the Micheal Muller in 2012. Before FANETs, MANETs were the best way to communicate in emergency situations, as they can be established quickly, easy to deploy and economical. MANETs employ grounded moving nodes which are capable to communicate each other without using pre-existing infrastructure. These networks are also known as grounded ad-hoc networks. MANETs have some limitations which force researchers to find a better solution for those situations where MANETs cannot be useful. Researcher’s wants to use the capability of UAV in ad-hoc network, so they developed single large UAV guided ad-hoc network. In this network, UAV collect the information and passes it to the grounded moving nodes which help grounded nodes to perform task efficiently. But single UAV based ad-hoc network cannot accomplish all the tasks by itself. Finally, research community came up with an idea of using multiple UAV to create ad-hoc networks. The idea behind the FANET is to overcome with limitations of grounded ad-hoc network by using the advantages of multiple UAVs together to perform tasks. In FANETs, a swarm of UAVs established communication link between them. They collect information and transfer it to the grounded nodes with the help of established links. Due to wide range of FANETs applications, research community is actively participating to formulate efficient infrastructure, routing and security mechanisms for FANETs.
FANET CONCEPT FANETs are basically adhoc network created by a group of UAVs, which is a new family of adhoc networks. Single UAV guided adhoc networks have some limitations as single UAV cannot collect information from whole geographical area in the operation independently. So, multiple UAVs are used to form adhoc networks called FANET. As, FANETs uses multiple UAVs, so they of improve scalability and flexibility ad-hoc networks. Each UAV is equipped of sensors, on-board monitor, GPS receiver and autopilot. The UAVs are fixed wings aircrafts with autopilot, capable of flying up to 12 m/s and up to 3 km/s in emergency situations. UAVs are available in different sizes for different applications. Different sizes of UAVs are: Micro UAVs, Low altitude and low endurance UAVs and high altitude and high endurance UAVs. The swarm of UAVs communicates among themselves and with the ground station. There is two type of communication:
UAV to UAV communication: In UAV to UAV communication, UAVs communicate with each other to complete the allocated task. Two UAVs can either directly communicate or through other UAVs. To communicate indirectly using multiple hopes, communication path is decided based of different routing strategies like reactive, proactive and hybrid routing. UAVs can have either short range or long range communication; it depends on required data transfer rate.
UAV to ground station communication: In UAV to ground station communication, UAVs connect to the ground stations to provide or receive information about various operations. Ground stations are basically known as base stations that instruct UAVs for various tasks.
Flying nodes have very high mobility and topological changes, so existing solutions of MANETs cannot be directly applied to FANETs. To formulate solutions for FANETs, either existing solutions can be modified or new techniques can be formulated. To establish communication between nodes various routing protocols found in literature. These protocols are categorized as follows:
Proactive routing protocol: In these protocols, each and every node in the network shares its routing information from its routing table at regular time interval which is used by the other nodes to identify the path for destination nodes and make the map of whole network. The big advantage of these protocols is that these protocols take very short time period to get the path to the destination. But, it costs very much bandwidth consumption to update the information within short period of time thorough which it maintain map of whole network. There are several proposed algorithms under this category like WRP, DSDV and OLSR Fisheye [8].
Reactive routing protocol: Reactive routing protocols are on-demand protocols, they build path whenever required by network nodes. The Reactive protocols do not broadcast their routing table information in regular time interval. They broadcast their routing information only when it is needed. Therefore, they minimize the use of network bandwidth. But, due to the reactive nature there is a disadvantage to these types of routing algorithms, End to End delay of packet delivery is increased as compared to proactive protocols. They also take more time to select an immediate node to transfer the data packet because of dynamic network topology. Reactive protocols are less likely to use in applications in dynamic environment. Many algorithms are proposed under this category like AODV, DSR and ABR.
Hybrid routing protocol: Hybrid protocols are combination of both proactive and reactive protocols. These protocols are designed to minimize the overhead which is occurred in both types of protocols [reactive and proactive]. But, the protocols under this category are not suitable for large networks having more than hundred nodes because of large overlapping of zones like ZRP.
FANET Design Considerations Due to distinctive features of FANET, it requires different design considerations than traditional ad-hoc networks. Here we discuss major design considerations : adaptability, latency, mobility, UAV platform constraints, scalability and bandwidth requirement.
Adaptability: FANET nodes are highly mobile in nature. Due to this behavior of nodes, they keep on changing their location [3]. The routes between UAVs keep changes and distance between them is also not constant. Another problem is UAV failure that decreases number of UAVs in networks. So the FANET design should consider these UAV failures and frequent path changes. Overall performance of network depends on the adaptability on these path changes and topology changes.
Latency: Latency is considered as one of the main design requirement of any network. Latency is basically application dependent factor. For real time applications of FANET like search and rescue operations, military applications latency should be low for transferring information. These are time bound applications. For non-time critical applications such as city architecture planning etc. the latency factor can be little compromised [5].
Mobility: Mobility of UAVs plays an important role in the performance of FANETs. There are several moment patterns for an adhoc network node. Moving pattern can be for group or individual node. It is very crucial to identify that which moving pattern of UAVs will be suitable to complete task effectively and in time bound manner.
UAV platform constraints : UAVs used in FANETs have limited payload capability, so they have certain constraints. Hardware weight effect the performance of UAVs, light payload increases the endurance. So an UAV with lighter payload have the scope for additional resources such as sensors and other peripheral devices. Another limitation faced by the UAVs used in FANETs is space limitation.
Scalability: Multi-UAVs can enhance the overall performance of network as compare to single UAV systems. Performance is enhanced by increasing number of UAVs in the network. Higher the number of UAVs, faster will be the task completion and more reliable will be the network. Scalability is important factor for time dependent applications.
Bandwidth requirement: In every FANET application, UAVs collects data from environment with the help of cameras and different sensors, collected data is transmit to ground base through multipath route. Data collected in applications such as monitoring, rescue, surveillance and battlefield is mainly high resolution video, images and audio. Also captured data is crucial and required to be transmitting with strict delay bound. So FANETs required high bandwidth resource to complete operation efficiently with in time bound.
FANET CHALLENGES FANET is the member of MANET family. FANET faces some additional challenges along with already existing challenges in MANET family due to its high node speed, high topology changes and mobility models. Based on the finding of literature review, following are the areas identified that require significant research to be done:
Routing: Routing in FANETs is different from other adhoc networks family. Node movement is relatively very high in FANETs. So the topology changes very frequently. One of the biggest challenges is to develop an efficient routing algorithm that not only able to work with high mobility nodes but should be quick to update its routing table frequently as the topology changes [7]. Security: Ensuring confidentiality, availability and Integrity of information during the communication between UAV to UAV communication and UAV to ground node communication is one of the major issues faced by FANETs [10]. Due to lack of physical security node compromise becomes easy in FANETs. Trust Management among nodes is another challenge due to high topology changes. Nodes join and leave the network very frequently. Secure routing is another point of concern in FANET [10].
FANET Security Layer Multi-layer Attacks Physical Layer Data Link Layer Network layer Transport layer Application layer
Table 2: Common attacks of FANET Attacks DoS, Impersonation, Replay, MIMA Intervention, Jamming, Snooping disruption MAC(802.11), bandwidth stealing, traffic monitoring, WEP weakness Black Hole, Link Spoofing, Worm-hole, Route tracking, Message fabrication, Byzantine Session hijacking, SYN Flooding Repudiation, data corruption
Quality of Service (QoS): In FANETs UAVs transmit data includes audio, video, images, text, GPS locations etc. To transfer such data FANETs should have a good quality of service with less delays and error rates. [2].
UAV Mobility and Placement: The placement of UAVs at appropriate location is one of the major research concerns in FANETs. UAVs of different capacity and capability are used for different purpose. Mini-UAVs are meant for carrying fewer payloads, like a thermal camera, single radar, camera, image sensor, etc. So, this is an open challenge to optimize the UAV placement to diminish energy feeding when the retrieved information is taking more time.
Network Scalability: Single UAV system can perform limited tasks. To perform task quickly and efficiently, collection of UAVs is required. This motivated the concept of multi-UAV based system [9]. Sometimes if during the task few UAVs are out of the network due to power or some
technical reason than it is required to add some new UAVs in the network to complete task efficiently. FANET algorithms should be designed in such a way so that they will be flexible to add any number of UAVs.
Reliable data delivery: FANET applications transfer very important information in different applications, which required to be delivered in time bound manner. So the reliability of the network should be very high. Reliability should be defined with the criticality of data.
FUTURE RESEARCH DIRECTIONS FANETs are getting more attention due to their capabilities in various situations. These networks have additional advantages from the traditional adhoc networks because they use flying agents to collect and transmit the information in the operation areas. Due to high speed of UAVs, these networks are highly dynamic and have high topology changes. To support data transition with dynamicity of these networks, an efficient routing scheme is required. So, developing appropriate routing protocols is one of the inspiring areas of research. Another explorative field of research in FANETs is appropriate size of flying node, its power consumption, range covered by node and speed of flying node. Along with communication and infrastructure needs, security of FANETs is also grabbing attention of researchers because FANETs carry sensitive and confidential information of critical application area. Security of flying nodes, trust management within nodes and secure routing are significantly important areas of research in FANETs.
CONCLUSION The capabilities and applications of FANETs are very prominent for complex areas. UAVs coordinate and communicate with each other to perform complex task efficiently and faster where ground communication does not work. The swarm of UAVs communicating with each other without the use of pre-existing infrastructure is termed as flying adhoc network. Aim of FANETs is to provide fast, reliable and secure communication services in the various application areas. Nodes in FANETs are highly mobile in nature and topology changes very frequently. Managing UAVs in FANET is very challenging task. In this article, basic concept of FANET, various applications and challenges are explained. This article aims to motivate the research community to come up with various solutions of the challenges faced in FANETs.
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