3GPP Release-18 Physical Layer Enhancements for IoT-NTN

The advent of mega satellite constellations has paved the way for bringing cellular connectivity to mobile broadband as well as Internet of Things (IoT) devices in unconnected or remote regions via satellites, thus complementing the terrestrial cellular coverage. With this motivation, the 3rd Generation Partnership Project (3GPP) introduced Non-Terrestrial Networks (NTN) support for IoT technologies including Long-Term Evolution (LTE) for Machine-Type Communications (LTE-MTC) and Narrowband Internet of Things (NB-IoT) in Release-17 (Rel-17), which are collectively known as IoT-NTN. Rel-17 IoT-ntn focused on only the essential changes to the existing IoT specification to enable IoT operation in satellite scenarios. IoT-NTN was further evolved in Rel-18 and several performance enhancements were introduced. In this article, an overview of the Rel-18 physical layer enhancements for IoT-ntn is provided. Specifically, a new feature related to disabling Hybrid Automatic Repeat reQuest (HARQ) feedback is described which helps mitigate the impact of HARQ stalling on throughput. Enhancements related to improving Global Navigation Satellite System (GNSS) operation are also discussed that enable the user equipment (UE) to maintain its uplink (UL) synchronization if its GNSS position becomes invalid during an ongoing connection. In addition, the performance evaluation of IoT-ntn technologies is presented in the context of International Mobile Telecommunications-2020 (IMT-2020) satellite performance requirements related to connection density.