  Cellular-connected unmanned aerial vehicle (UAV) has attracted a surge of
research interest in both academia and industry. To support aerial user
equipment (UEs) in the existing cellular networks, one promising approach is to
assign a portion of the system bandwidth exclusively to the UAV-UEs. This is
especially favorable for use cases where a large number of UAV-UEs are
exploited, e.g., for package delivery close to a warehouse. Although the nearly
line-of-sight (LoS) channels can result in higher powers received, UAVs can in
turn cause severe interference to each other in the same frequency band. In
this contribution, we focus on the uplink communications of massive
cellular-connected UAVs. Different power allocation algorithms are proposed to
either maximize the minimal spectrum efficiency (SE) or maximize the overall SE
to cope with severe interference based on the successive convex approximation
(SCA) principle. One of the challenges is that a UAV can affect a large area
meaning that many more UAV-UEs must be considered in the optimization problem,
which is essentially different from that for terrestrial UEs. The necessity of
single-carrier uplink transmission further complicates the problem.
Nevertheless, we find that the special property of large coherent bandwidths
and coherent times of the propagation channels can be leveraged. The
performances of the proposed algorithms are evaluated via extensive simulations
in the full-buffer transmission mode and bursty-traffic mode. Results show that
the proposed algorithms can effectively enhance the uplink SEs. This work can
be considered the first attempt to deal with the interference among massive
cellular-connected UAV-UEs with optimized power allocations.
