IEEE Technology and Society Magazine - June 2016 - 70

weather conditions, and geographical uncertainties. All
of these factors are responsible for topological changes
that cause increased overhead routing, delays, and low
packet delivery success rates. The topology change rate
can be neglected by enlarging the transmission range of
the UAVs, i.e., employing a MAC layer protocol that supports a large transmission range. The trade-off for
adopting this solution will be complexity and energy
consumption, but UAVs have enough hardware support
to accommodate such issues.

Low Latency Requirement
Search and destroy operations and disaster monitoring require minimal latency, as the information needs
to be transmitted at a very high rate. A crude way to
create minimal latency is to decrease hop counts
with long transmission ranges, resulting in improved
latency results. Moreover, the concept of priority
schemes can also be used in FANETs [22]. Prioritybased routing protocols can be used to attain different QoS for various message types. Congestion
control protocols are vital for performing efficient
collision control and coordination among UAVs [23].
An appropriate choice of protocol suite can address
the demand of delay bounds.

High Reliability
Affordability and accessibility of UAVs are determined
by their reliability factor. FANETs are used in sensitive
military and monitoring applications that require guaranteed data delivery. With FANETs, reliability is achieved
by forming an ad-hoc network between UAVs so that if a
UAV experiences a failed link, it can still communicate

with the infrastructure via other UAVs. In the absence of
an ad-hoc setup amid UAVs, each UAV needs to be connected to the infrastructure. Under such a scenario, if a
UAV fails, important mission-related information can be
lost. Also, routing protocols based on data aggregation
can serve the demand of highly accurate data [24]. In
such protocols, data loss due to link failures is
addressed by allowing the intended destination to
request certain data from other UAVs in the network,
thus ensuring the receipt of fully reliable information for
military and monitoring centric applications.

FANET Communication Types
There are twomain types of UAV communication for
FANETs: UAV-to-UAV and UAV-to-infrastructure. In UAVto-UAV communication information is exchanged
between UAVs without a central controller using different routing algorithms. Since FANET topology changes
due to removal or addition of new UAVs, maintaining
efficient UAV-to-UAV communication leads to several
research directions. Robust routing protocols that can
guarantee a packets' delivery from source UAV to destination UAV are being explored. Moreover, reducing
packet latency between UAVs due to rapid scenario
changes is also an important research area.
UAV-to-infrastructure communication is formulated
by a subgroup of UAVs communicating with the infrastructure, i.e., a satellite or ground station. This type of
communication conveys information about intended
tasks over a wider scale and requires the exchange of
heavier data payloads. Extended communication ranges
are required for the exchange of messages between
UAV and infrastructure.

FANET Design Considerations
Cluster 1

FANETs are characterized by rapid changes and activities during network operation. The design should be
highly scalable with adaptive path planning and robust
communication protocols. Some insight on these technical requirements is given below.

Topologies
Clusterhead
Communication

Cluster 3
Cluster 2

FIGURE 2. Clustered FANET scenario (Clouds courtesy of pptbackgrounds.net).

In order to maintain coordination and collaboration,
peer-to-peer connections are formed between UAVs in a
FANET scenario. The tasks can be completed using single cluster or multicluster formations [25]. Single cluster
networks serve best for homogenous and small scale
missions. However, the need for multicluster networks
arises when certain UAVs have to perform multiple missions covering wide terrains. The cluster head of each
cluster in multicluster FANETs is not only designated to
carry downlink communication, but to also communicate with cluster heads of other clusters. The clusters
may be in same or different mission areas and serve to

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