An Overview of Medium Access Control Protocols in Machine-Type Communication Satellite Internet-of-Things Networks

Interference is one of the critical challenges in MTC–satellite networks. There are several reasons why most classical terrestrial MAC protocols are not efficient to support massive SIoT connectivity demands. First of all, a non‐terrestrial MTC gateway deployed on a satellite is likely to receive a large number of uplink radio packets from the end devices deployed within its footprint area. Secondly, the hundreds to thousands of kilometers of communication distance between an end device and a satellite introduce a time‐varying propagation delay. Third, the LEO satellite mobility introduces dynamic Round Trip Time (RTT) and high Doppler shift, which results in time and frequency synchronization problems. To give a few examples, Time‐Division Multiple Access (TDMA) ensures high reliability at the cost of high overhead and potential inefficiency in resource usage, causing unwanted delays. TDMA also requires a central control system for frame synchronization and resource allocation, which makes uplink communication challenging in satellite networks. Similarly, time synchronization is hard to achieve when using TDMA for LEO satellites. Carrier Sense Multiple Access (CSMA) protocols are not feasible in satellite networks due to the large footprint and consequent hidden node problem. If not carefully accounted for, the interfering radio signals can significantly degrade the SIoT network performance due to possible destructive collisions. In this chapter, we offer an overview of the LEO satellite system and some requirements of SIoT networks and discuss the relevant MAC protocols and performance metrics. We present and briefly review MAC protocols that have the potential to support massive uplink connectivity and can offer scalable direct‐to‐satellite IoT communication. We also highlight the key trade‐offs, pros, and cons. Finally, we identify some open challenges and future research directions to investigate MAC protocol designs for LEO satellite IoT networks.