  Airborne base stations (carried by drones) have a great potential to enhance
coverage and capacity of cellular networks. Multiple scenarios and use cases
will highly benefit from such technology such as (i) offloading terrestrial
base stations (BSs) in dense and urban areas, and (ii) providing coverage for
rural areas. However, one of the main challenges facing the deployment of
airborne BSs is the limited available energy at the drone, which limits the
flight time. In fact, most of the currently used unmanned aerial vehicles
(UAVs) can only operate for one hour maximum. This limits the performance of
the UAV-enabled cellular network due to the need to frequently visit the ground
station to recharge, leaving the UAV's coverage area temporarily out of
service. In this article, we propose a new UAV-enabled cellular network setup
based on tethered UAVs (TUAVs). In the proposed setup, the TUAV is connected to
a ground station (GS) through a tether, which provides the TUAV with both
energy and data. This enables a flight that can stay for days. We describe in
detail the components of the proposed system. Furthermore, we enlist the main
advantages of a TUAV-enabled cellular network compared to typical untethered
UAVs. Next, we discuss the potential applications and use cases for TUAVs.
Finally, we discuss the challenges, design considerations, and future research
directions to realize the proposed setup.
