  Current fifth-generation (5G) networks do not cover maritime areas, causing
difficulties in developing maritime Internet of Things (IoT). To tackle this
problem, we establish a nearshore network by collaboratively using on-shore
terrestrial base stations (TBSs) and tethered unmanned aerial vehicles (UAVs).
These TBSs and UAVs form virtual clusters in a user-centric manner. Within each
virtual cluster, non-orthogonal multiple access (NOMA) is adopted for agilely
including various maritime IoT devices, which are usually sparsely distributed
on the vast ocean. The nearshore network also shares spectrum with marine
satellites. In such a NOMA-based hybrid satellite-UAV-terrestrial network,
interference among different network segments, different clusters, as well as
different users occurs. We thereby formulate a joint power allocation problem
to maximize the sum rate of the network. Different from existing studies, we
use large-scale channel state information (CSI) only for optimization to reduce
system overhead. The large-scale CSI is obtained by using the position
information of maritime IoT devices. The problem is non-convex with intractable
non-linear constraints. We tackle these difficulties by adopting the max-min
optimization, auxiliary function method, and successive convex approximation
technique. An iterative power allocation algorithm is accordingly proposed,
which is shown effective for coverage enhancement by simulations. This shows
the potential of NOMA-based hybrid satellite-UAV-terrestrial networks for
maritime on-demand coverage.
