The evolution of mobile communication technology from 5G to 6G is increasingly integrating non-terrestrial networks (NTNs) into global communication infrastructures. A recent review published in Engineering titled “Non-Terrestrial Networking for 6G: Evolution, Opportunities, and Future Directions” by Feng Wang, Shengyu Zhang, Huiting Yang, and Tony Q.S. Quek, provides an in-depth analysis of the role of NTNs in the development of 6G networks, focusing on key technologies and challenges.

NTNs, which include geostationary-Earth-orbit (GEO), medium-Earth-orbit (MEO), low-Earth-orbit (LEO) satellites, and high-altitude platforms (HAPs), are poised to deliver reliable services to remote regions on Earth. The review highlights that NTNs can provide network connectivity to any corner of the Earth, which is particularly vital in areas where terrestrial network (TN) coverage is insufficient or economically unfeasible. The development of LEO constellations is spearheading the evolution of NTN construction due to their proximity to Earth, enabling low-latency network connectivity and increased radio link budgets compared with higher orbit satellites.

However, the extensive coverage and rapid movement of satellites pose unique challenges in user equipment access and inter-satellite transmission, impacting the quality of service and service continuity. The review notes that “the extensive coverage and dynamic features of NTNs offer opportunities for ubiquitous access. However, they also present unique challenges in terms of managing real-time, dynamic, and massive connectivities due to the large satellite coverage and coverage overlap in multi-constellation environments.”
The paper discusses several key areas of NTN development, including radio resource management, satellite mobility, and onboard traffic scheduling. In terms of radio resource management, the review emphasizes the importance of accurate channel state information (CSI) and efficient beamforming strategies. The authors state that “accurate CSI is essential, as it allows for informed resource-allocation decisions and the formulation of strategies to mitigate signal interference.” However, acquiring CSI in NTNs is complex due to the rapid movement of LEO satellites.

In the context of satellite mobility, the review highlights the need for efficient handover (HO) mechanisms to manage the frequent transitions between satellite coverages. The authors propose preconfigurable HO sequences and conditional HO techniques to reduce signaling overhead and improve service continuity. They note that “a preconfigured NTN HO sequence can reduce signaling interactions between satellites and UEs and among the satellites themselves, increasing the HO success rate.”

The review also explores the role of network slicing in software-defined NTNs (SD-NTNs), which allows for the creation of multiple isolated virtual networks over a shared physical infrastructure. This technology is crucial for meeting the diverse service requirements of different applications, such as enhanced mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC), and massive machine-type communication (mMTC). The authors suggest that “network slicing in SD-NTNs presents challenges due to satellite fast motion, resource constraints, and diverse service demands.”

Looking ahead, the review identifies several open problems and future research directions, including interference management in NTNs, fine-tuned TN–NTN unification, and reliability-enhanced network slicing. The authors emphasize the need for robust, fault-tolerant mechanisms to ensure network reliability in the face of hardware failures, link interruptions, and environmental conditions.

The review underscores the transformative potential of NTNs in the evolution of 6G networks, offering insights into the challenges and opportunities associated with their deployment. The integration of NTNs into future communication systems promises to extend global connectivity and enhance service capabilities, particularly in underserved regions.

The paper “Non-Terrestrial Networking for 6G: Evolution, Opportunities, and Future Directions,” is authored by Feng Wang, Shengyu Zhang, Huiting Yang, Tony Q.S. Quek. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.05.013. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.