  In this paper, we focus on the use of Low-Eart Orbit (LEO) satellites
providing the Narrowband Internet of Things (NB-IoT) connectivity to the
on-ground user equipment (UEs). Conventional resource allocation algorithms for
the NBIoT systems are particularly designed for terrestrial infrastructures,
where devices are under the coverage of a specific base station and the whole
system varies very slowly in time. The existing methods in the literature
cannot be applied over LEO satellite-based NB-IoT systems for several reasons.
First, with the movement of the LEO satellite, the corresponding channel
parameters for each user will quickly change over time. Delaying the scheduling
of a certain user would result in a resource allocation based on outdated
parameters. Second, the differential Doppler shift, which is a typical
impairment in communications over LEO, directly depends on the relative
distance among users. Scheduling at the same radio frame users that overcome a
certain distance would violate the differential Doppler limit supported by the
NB-IoT standard. Third, the propagation delay over a LEO satellite channel is
around 4-16 times higher compared to a terrestrial system, imposing the need
for message exchange minimization between the users and the base station. In
this work, we propose a novel uplink resource allocation strategy that jointly
incorporates the new design considerations previously mentioned together with
the distinct channel conditions, satellite coverage times and data demands of
various users on Earth. The novel methodology proposed in this paper can act as
a framework for future works in the field.
