  In this paper, we consider an overlay satellite-terrestrial network (OSTN)
where an opportunistically selected terrestrial IoT network assist primary
satellite communications as well as access the spectrum for its own
communications in the presence of combined interference from extra-terrestrial
and terrestrial sources. Hereby, a power domain multiplexing is adopted by the
IoT network by splitting its power appropriately among the satellite and IoT
signals. Relying upon an amplify-and-forward (AF)-based opportunistic IoT
network selection strategy that minimizes the outage probability (OP) of
satellite network, we derive the closed-form lower bound OP expressions for
both the satellite and IoT networks. We further derive the corresponding
asymptotic OP expressions to examine the achievable diversity order of two
networks. We show that the proposed OSTN with adaptive power splitting factor
benefits IoT network while guaranteeing the quality of service (QoS) of
satellite network. We verify the numerical results by simulations.
