An Overview of Mobility Enhancements for Non-Terrestrial Networks in 3GPP 5G NR System

Non-Terrestrial Networks (NTN) are envisioned to provide ubiquitous connectivity for next-generation wireless communication systems. However, due to the unique characteristics of the NTN environment, such as low signal strength variation and long propagation delay, users may experience non-robust handover. To address these challenges and enhance the user experience, the 3rd Generation Partnership Project (3GPP) has studied mobility enhancements for NTN since Release 17. Two mechanisms initially designed for Terrestrial Networks, Random Access Channel-less Handover and Conditional Handover, have been adapted and extended to suit the NTN scenario. In addition, a novel mobility enhancement called satellite switching with resynchronization was introduced in 3GPP Release 18, aiming to reduce signaling overhead and improve handover efficiency in satellite communication scenarios. This article provides an overview of the mobility enhancements for NTN in the 3GPP 5G New Radio system, along with a technical background detailing the key modifications and new features introduced to address the distinct challenges of satellite-based communication environments.