UAVs are equipped with radio-communication
devices and rely on unmanned autonomous flight-control programs, which have
been actively developed around the world. Given their low cost, flexible
maneuvering capability, and unmanned operation, UAVs have been widely used in
both civilian operations and military missions, including aerial mapping,
disaster rescue, agricultural irrigation, and military surveillance and attack.
Based on their cruise duration and action
radius, UAVs can be categorized into the following four types.
- The high-altitude and long-endurance UAVs are applied in high-altitude reconnaissance, interception,
and attack, as exemplified by the American Global Hawks and Predator UAVs and
by the Israeli Commando UAVs.
- The medium-range UAVs, having an action radius between 700 and 1,000 km, are primarily designed for
moderate-range reconnaissance and combat-effect assessment. The American Air
Force D-21 UAVs and 350 UAVs are both typical medium-range representatives.
- The low-cost, short-range small UAVs have an action radius of fewer than 350 km and a takeoff weight of less
than 50 kg, such as the British Phoenix, French Marthe, and Israeli Scout UAVs;
their flight altitude is fewer than 3 km, and flight span is about four hours.
- The mini drones have a more limited cruising speed, ranging from 10 to 30 km/h and a cruising duration of
no fewer than 30 min. The weight of mini drones is usually lower than 1 km.
However, in the rest of this article, we focus our attention on both the
lower-cost and lower-velocity small or mini drones.
Although UAVs have indeed matured, the
proliferation of small- or mini-drone application scenarios and the
sophistication of their functionality can only be exploited with the aid of
multi-UAV cooperation, networking, communication, and coordinated control.
Furthermore, ad hoc networking, task assignment, and dynamic negotiation among
cooperating drones are also beneficial in terms of extending the UAV
functionalities and their coverage and increasing their efficiency.
Relying on the association of UAVs
voluntarily joining to meet their common goals through a jointly owned and
democratically controlled unit, the concept of the cooperative multi-UAV system
is proposed, which contains the sensor unit, the communication unit, and the
information processing unit.
However, the challenge is that the movement
of UAVs leads to time-variant network topologies and to frequent link outages.
Additionally, the agile flight states (i.e., the yaw, pitch, or roll angles)
impose grave performance erosion and are a substantial waste of communication
resources and energy. These practical issues motivated us to conceive this
article on the cooperation and collaboration of multi-UAV networks.
This article begins with a detailed survey
of the multi-UAV networking technologies and the protocol architecture.
Moreover, we investigate two critical issues of the cooperative distributed UAV
networks, namely, distributed gateway-selection algorithms and the stability-control
regimes. Specifically, acting as cluster heads, the gateways constitute the
bottleneck and limit the network's reliable connectivity and stability.
Finally, as our original contributions, an
efficient gateway-selection mechanism and a cloud-based stability-control
regime for cooperative small- or mini-drone-based UAV networks are introduced,
complemented by a range of open challenges.
Full article: IEEE Vehicular Technology
Magazine, Volume 12, Number 3, September 2017