  This paper presents a star-of-star topology for internet-of-things (IoT)
networks using mega low-Earth-orbit constellations. The proposed topology
enables IoT users to broadcast their sensed data to multiple satellites
simultaneously over a shared channel, which is then relayed to the ground
station (GS) using amplify-and-forward relaying. The GS coherently combines the
signals from multiple satellites using maximal ratio combining. To analyze the
performance of the proposed topology in the presence of interference, a
comprehensive outage probability (OP) analysis is performed, assuming imperfect
channel state information at the GS. The paper employs stochastic geometry to
model the random locations of satellites, making the analysis general and
independent of any specific constellation. Furthermore, the paper examines
successive interference cancellation (SIC) and capture model (CM)-based
decoding schemes at the GS to mitigate interference. The average OP for the
CM-based scheme and the OP of the best user for the SIC scheme are derived
analytically. The paper also presents simplified expressions for the OP under a
high signal-to-noise ratio (SNR) assumption, which are utilized to optimize the
system parameters for achieving a target OP. The simulation results are
consistent with the analytical expressions and provide insights into the impact
of various system parameters, such as mask angle, altitude, number of
satellites, and decoding order. The findings of this study demonstrate that the
proposed topology can effectively leverage the benefits of multiple satellites
to achieve the desired OP and enable burst transmissions without coordination
among IoT users, making it an attractive choice for satellite-based IoT
networks.
