Challenges and Future Directions in Integrated Terrestrial-Non-Terrestrial Networks

Dear Colleagues,

In Release 17, the Third Generation Partnership Project (3GPP) initiated the standardization process for non-terrestrial networks (NTNs) to extend the capabilities of 5G new radio (NR) to support satellite and aerial communication. This release established NTNs as a critical component of 5G networks, explicitly identifying satellites, unmanned aerial vehicles (UAVs) and high-altitude platforms (HAPs) as key use cases. Furthermore, Release 17 introduced a foundational set of features enabling 5G NR operation over NTNs within Frequency Range 1 (FR1).

Building on this foundation, Release 18 has already introduced enhancements for 5G NR NTN, and the ongoing Release 19 is expected to further enhance 5G NR NTN, introducing regenerative payload, downlink coverage enhancements, uplink capacity/throughput enhancements, etc.

One of the key advantages of the NTN is its extensive coverage capabilities and the capacity to provide resiliency. However, integrating NTNs with TNs poses significant technical challenges.

In fact, compared to TNs, NTNs exhibit several distinctive characteristics, including highly dynamic network topologies, specific channel models and impairments (i.e., the Doppler shift and high delay), and technological constraints, e.g., power limitations. As a result, solutions designed for terrestrial networks may not be directly applicable to NTNs. Therefore, it is necessary to develop novel techniques tailored to the unique challenges posed by NTNs, some of which will leverage native AI-based approaches.

Furthermore, NTNs are expected to coexist within the existing spectrum, necessitating efficient dynamic spectrum access strategies, spectrum reuse mechanisms, and co-channel spectrum management.

As research and standardization initiatives for the evolution of beyond 5G (B5G) are in progress and 6G activities were kickstarted by the 3GPP workshop on 6G (held on 10–11 March 2025), this Special Issue aims at presenting a collection of cutting-edge technical papers from academia, industry, and standardization bodies, addressing major advancements and transformative trends for the NTN component of 6G, targeting both infrastructural and technological aspects. These include the heterogeneity of NTN nodes and the complexity associated with provisioning services across multi-layered, multi-frequency, and multi-mission networks, additionally addressing sustainability aspects.

Motivated by current trends in the field of integrated TNs and NTNs, we seek to garner cross-cutting and high-quality original research papers, focusing on, but not limited to, the following areas:

• Flexible, intelligent, and reconfigurable payloads for NTNs;
• Network slicing and orchestration;
• SDN/NFV and network disaggregation for integrated TNs and NTNs;
• Cloud continuum (e.g., orbital edge computing);
• Multiple access schemes, e.g., RSMA and NOMA for integrated TN-NTN networks;
• Adaptive antennas and MIMO;
• Distributed beamforming for satellite swarms;
• Backscatter communications for integrated TN-NTN networks;
• Mobility and handover management for integrated TN-NTN networks;
• AI for integrated TN-NTN networks;
• Optimized NTN-NTN and TN-NTN radio resource allocation, the scheduling of communication and computation, network optimization, and routing design;
• Spectrum management, spectrum sharing and engineering;
• Energy harvesting, wireless information, and power transfer for integrated TN-NTN networks;
• Error control, modulation and waveform design, and MAC layer design;
• The cost- and power-efficient design of integrated TN-NTN networks;
• Sustainability aspects for integrated TN-NTN;
• Quantum satellite communications;
• Satellite communications within 3GPP;
• Positioning with LEO satellites;
• Sensing and communication in NTNs;
• Energy-efficient AI onboard process in NTNs.

Dr. Carla Amatetti
Dr. Estefania Recayte
Dr. Dorin Panaitopol
Dr. Alessandro Guidotti
Dr. Flor Ortiz
Guest Editors

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• NTN
• 6G
• 5G
• routing
• mega-constellation
• AI
• RRM
• integrated networks