Packet Collision Probability Analysis in Contention-Based Direct-to-Satellite IoT Uplink

This paper considers a direct-to-satellite Internet of Things system where nodes on ground contend to deliver data packets to a low Earth orbit satellite, during its pass. In this framework, the paper focuses on the collision probability between the packets transmitted by the uncoordinated contending devices. An exact and closed-form expression for this probability is derived that considers both the satellite velocity and the different contention time widows the devices may have, depending on their positions on ground. The analytical expression, valid for a wide range of different shapes of the satellite spot, is validated by comparison with numerical simulations. Usage of the developed expression to upper bound the packet loss probability over realistic channels is discussed.