5G-NTN (Non-Terrestrial Networks) Overview

What is Non-Terrestrial Network (NTN), and why is it considered a crucial element for future communication?

Non-Terrestrial Networks (NTN) typically refer to communication networks that do not rely solely on traditional terrestrial infrastructure, such as land-based cellular towers or fiber optic cables. Instead, NTN leverages various non-terrestrial technologies and platforms to provide connectivity.

Here are some key elements and examples of NTN:

  • Satellite Networks: One of the most common forms of NTN is satellite communication. Satellites in geostationary orbit or in lower Earth orbits (LEO) can provide broadband internet access, telecommunication services, and data connectivity to remote and underserved areas.
  • High-Altitude Platforms (HAPs): HAPs are platforms that float at high altitudes in the Earth’s atmosphere, such as stratospheric balloons or solar-powered drones. They can serve as relay stations for wireless communication and internet access.
  • Aerial Platforms: Some NTN solutions use drones or other aerial vehicles equipped with communication equipment to create temporary communication networks, especially in disaster-stricken areas or during events where traditional infrastructure is insufficient.
  • Underwater Communication Networks: While not always included in the term NTN, underwater communication networks are another example of non-terrestrial connectivity. These networks are used for applications such as oceanographic research, underwater surveillance, and offshore energy operations.
  • Hybrid Approaches: Some NTN solutions combine various technologies, such as a combination of satellites and high-altitude platforms, to extend network coverage and improve reliability.

Non-terrestrial network typical scenario based on transparent payload.

Non-Terrestrial Networks (NTN) offer several benefits and advantages across various applications and industries. Here are some of the key benefits of NTN:

  • Extended Coverage: NTN extends network coverage to remote and underserved areas where traditional terrestrial infrastructure is lacking or economically unfeasible. This helps bridge the digital divide by bringing connectivity to rural and isolated regions.
  • Disaster Resilience: NTN serves as a crucial backup communication option during natural disasters and emergencies when terrestrial networks may be damaged or overwhelmed. This ensures that essential communication and services remain available when they are needed most.
  • Global Connectivity: Satellite-based NTN provides global coverage, making it ideal for applications that require connectivity across vast and remote areas, such as maritime and aviation industries, as well as global supply chain tracking.
  • IoT Enablement: NTN supports Internet of Things (IoT) applications by providing connectivity for monitoring assets, infrastructure, and environmental conditions in remote locations. It is optimized for low-power IoT devices and applications with small data exchange requirements.
  • Broadcasting and Multicast: Satellite-based NTN excels at broadcasting data and content over wide geographic areas, making it valuable for delivering consistent information to large audiences. This capability is beneficial for applications like mobile gaming and emergency alerts.
  • Global Roaming: NTN enables seamless connectivity for applications that require continuous communication as they move across different modes of transport, such as tracking containers from ships to trucks.
  • Network Capacity Offload: In densely populated urban areas, NTN can help offload traffic from terrestrial networks, reducing congestion and improving overall network performance.
  • Low-Power IoT Support: NTN is optimized for low-power communication, making it suitable for IoT devices in remote or battery-powered applications where conserving energy is essential.
  • Future-proofing: As the demand for data and connectivity continues to grow, NTN provides a scalable solution to expand network capacity and coverage without solely relying on terrestrial infrastructure.
  • Cost-Effective Solutions: In some scenarios, building and maintaining traditional terrestrial networks may not be cost-effective. NTN can offer more affordable alternatives for connectivity, especially in areas with low population density.
  • Versatility: NTN solutions come in various forms, including satellites, high-altitude platforms, drones, and underwater communication networks. This versatility allows NTN to adapt to specific use cases and industries.
  • Enhanced Mobile Edge Computing: NTN can support 5G mobile edge applications by providing distributed computing and content delivery capabilities in remote and diverse geographic locations.

While Non-Terrestrial Networks (NTNs) have several advantages, they also come with certain disadvantages and challenges. Here are some of the potential disadvantages of 5G NTNs:

  • Antenna technology: Antenna technology in Non-Terrestrial Networks is vital for communication, with efforts to minimize size and explore electronic direction adjustment while considering cost constraints.
  • High Initial Deployment Costs: Building and launching satellites or deploying high-altitude platforms can be expensive. The initial infrastructure investment for NTN can be substantial.
  • Latency: Satellite-based NTN systems can introduce higher latency compared to terrestrial networks. This latency can affect real-time applications like online gaming or video conferencing.
  • Limited Spectrum: Satellites and other NTN platforms operate within allocated frequency bands, and spectrum availability is finite. As more services and applications use NTN, spectrum congestion could become an issue.
  • Space Debris and Saturation: In low Earth orbit (LEO), satellites can contribute to the growing problem of space debris. Saturation of LEO with satellites from multiple providers raises concerns about collisions and space sustainability.
  • Weather and Environmental Factors: Satellite communication can be affected by adverse weather conditions, such as heavy rain or atmospheric interference, which can disrupt signals and reduce reliability.
  • Regulatory Challenges: Operating NTNs often requires coordination with regulatory bodies and adherence to international agreements. Navigating complex regulatory environments can be challenging.
  • Signal Interference: The signals from NTNs can sometimes interfere with each other or with terrestrial networks, leading to potential disruptions in communication.
  • Security and Privacy Concerns: Data transmitted via satellite or other NTN technologies can be vulnerable to interception or hacking. Ensuring the security and privacy of communications is a critical concern.
  • Limited Bandwidth per User: Despite advances in technology, satellite networks may still have limited bandwidth available for each user, which could result in reduced data speeds during periods of high demand.
  • Deployment and Maintenance Challenges: Maintaining and servicing satellite and aerial platforms can be logistically challenging, especially in remote or inaccessible areas.
  • Complex Handover: Seamless handovers between terrestrial and non-terrestrial networks can be technically complex, potentially leading to service interruptions when transitioning between network types.
  • Energy Consumption: Some NTN platforms, such as drones or high-altitude balloons, may have significant energy consumption requirements, which could limit their operational duration or increase operational costs.

  • Sat-Gateways: These are essential components that establish the connection between the Non-Terrestrial Network (NTN) and public data networks, acting as gateways for communication.
  • GEO Satellite Coverage: GEO (Geostationary Earth Orbit) satellites are linked to one or more sat-gateways to provide extensive coverage over a targeted area, which can range from regional to continental. Each cell’s user equipment is typically served by a single sat-gateway, ensuring efficient connectivity.
  • Non-GEO Satellite Mobility: Non-GEO satellites are served successively by different sat-gateways. This system is designed to guarantee continuity in both service and feeder links as the satellite switches between these gateways. This allows for smooth mobility anchoring and handover processes. Optionally, service discontinuity can also be implemented.

Overall illustration of an NTN

  • Feeder Links: These links represent the radio connections between the sat-gateways and the satellites, facilitating the exchange of data and signals.
  • Service Links: These radio links establish communication channels between the user equipment (UE) and the satellite, enabling data transfer and connectivity for users within the targeted service area.
  • Satellite Payload: Satellites implementing a transparent payload generate multiple beams over a specified service area. The satellite’s field of view defines the coverage area, which can be shaped as earth-fixed beams or earth-moving beams for Low Earth Orbit (LEO) satellites. The beam footprints are typically elliptical in shape and depend on the onboard antenna design and minimum elevation angle.
  • Transparent Payload Features: The transparent payload includes critical components such as radio frequency filtering, frequency conversion, and signal amplification. These features ensure that the waveform signal repeated by the payload remains unaltered, preserving signal integrity throughout the communication process.
  • User Equipment (UE): Within the targeted service area, user equipment, such as mobile devices or communication terminals, is served by the satellite. This enables users to access the network and enjoy connectivity services provided by the NTN system.

The airborne category includes Unmanned Aircraft Systems (UAS) platforms, usually positioned at altitudes of 8 to 50 km, including High Altitude Platform Systems (HAPS) at 20 km altitude.

  • UAS, like GEO satellites, can maintain a fixed position relative to a specific ground point, with beam footprints varying from 5 to 200 km.
  • Spaceborne and airborne platforms fall into two distinct configurations based on their payload.
  • NTN platforms are equipped with either transparent or regenerative payloads.
  • GEO satellites – offer coverage at the continental, regional, or local level.
  • LEO satellite – constellations can deliver services across both Northern and Southern hemispheres and, in some cases, achieve global coverage, including polar regions, by adopting specific orbit inclinations and generating a sufficient number of beams.
  • Medium Earth Orbit (MEO) satellite -Medium Earth Orbit (MEO) satellites are positioned in a middle-altitude orbit, offering a balance between coverage and latency for various communication applications.
PlatformsAltitude RangeOrbitTypical Beam Footprint Size
Low-Earth Orbit (LEO) satellite300 – 1500 kmCircular around the Earth100 – 1000 km
Geostationary Earth Orbit (GEO) satellite35,786 kmNotional station keeping position fixed in terms of elevation/azimuth with respect to a given Earth point200 – 3500 km
Medium Earth Orbiting (MEO) satellite7000 to 25000 kmcircular orbit around Earth100 – 1000 km

The efforts within Technical Specification Group (TSG) RAN and TSG SA for Rel-17 NTN and satellite work items have been advancing steadily, with the aim of integrating satellite capabilities into 3GPP technical specifications.

In the future, ESOA members and other Non-Terrestrial Network (NTN) stakeholders initiated discussions during the 3GPP Rel-18 June workshop, and they are presently engaged in developing additional improvements for both NR-NTN and IoT-NTN, which will be taken into account for Rel-18.

Non-Terrestrial Networks (NTN) have several valuable use cases across various industries and applications. Here are some prominent use cases for NTN:

  • Rural Connectivity: NTN can bridge the digital divide by providing internet and communication services to remote and underserved rural areas where terrestrial infrastructure is lacking.
  • Disaster Response: During natural disasters or emergencies, when terrestrial networks may be disrupted, NTN ensures critical communication, aiding in search and rescue operations and providing essential information to affected populations.
  • Maritime and Aviation Communication: NTN enables continuous connectivity for ships, aircraft, and maritime and aviation operations in remote or oceanic regions where terrestrial coverage is limited.
  • Agriculture: In precision agriculture, NTN supports IoT applications for monitoring crops, weather conditions, and equipment in vast agricultural areas.
  • Mining and Energy Sector: Remote mining and energy operations benefit from NTN for real-time monitoring, automation, and communication in challenging environments.
  • IoT and Asset Tracking: NTN facilitates asset tracking and monitoring for various industries, including logistics, shipping, and transportation, where continuous global coverage is essential.
  • Global Supply Chain: NTN helps track and trace goods globally, ensuring supply chain visibility and security.
  • Broadcasting and Content Delivery: For wide-area broadcasting, such as mobile gaming or emergency alerts, NTN provides efficient content distribution over large geographic regions.
  • Global Roaming: Applications like tracking and tracing of containers require seamless connectivity across satellite and terrestrial networks, supporting international logistics and transportation.
  • Low-Power IoT: NTN is optimized for low-power IoT devices and applications, making it suitable for remote sensor deployments and environmental monitoring.
  • Edge Computing: NTN can support 5G mobile edge applications by providing distributed computing and content delivery capabilities in diverse geographic locations.
  • Offloading Terrestrial Networks: In densely populated urban areas, NTN can alleviate congestion by offloading traffic from terrestrial networks, improving overall network performance.
  • Future-Proofing: As the demand for data and connectivity continues to grow, NTN offers a scalable solution to expand network capacity and coverage.
  • Cost-Effective Connectivity: In areas with low population density where building and maintaining traditional terrestrial networks is costly, NTN can offer more affordable alternatives for connectivity.

Transparent payload

  • In a Transparent Payload scenario, the satellite operates as an analog radio frequency repeater.
  • Digital processing is done at gNB at GW.
  • It serves both the feeder and service links without modifying the transmitted signals.
  • Specifically in the context of 5G, the satellite, including Unmanned Aerial Systems (UAS), acts as a medium for replicating the 5G NR-Uu radio interface.
  • The satellite does not alter the signals passing through it.
  • It ensures the seamless transmission of data from the feeder link to the service link.
  • This mode simplifies satellite’s role to relay 5G signals without making changes to the content or format of the data.

Reference: 38.821-Transparent Payload

Non-Transparent (Regenerative) payload:

The satellite plays a central role in signal regeneration, bridging communication between Earth and the satellite network.

  • The NR-Uu interface functions on the service link, facilitating communication with user equipment.
  • On the feeder link, the satellite employs N2 and N3 interfaces, forming a satellite radio interface.
  • This setup effectively positions the gNB (5G base station) within the satellite, enabling enhanced signal processing and relay capabilities.
  • The regenerative payload actively enhances signals, which can include error correction, modulation/demodulation, and amplification.
  • Regenerative payloads support bidirectional communication, enabling data exchange between Earth-based stations and user equipment through the satellite.
  • Data may undergo transformation within the payload to align with satellite network requirements, ensuring efficient and reliable transmission.
  • Operators gain increased control over signal quality, network performance, and data integrity.
  • Implementing a regenerative payload adds complexity and cost to satellite systems, but it offers substantial advantages in terms of signal optimization and network reliability.

Reference: 38.821 Non-Transparent or Regenerative Payload

Table 5.2.2-1: NTN satellite bands in FR1

SIB 19 Role in NTN:

In the context of Non-Terrestrial Networks (NTN), System Information Block 19 (SIB 19) continues to play a crucial role, especially in satellite-based communication systems. While the core purpose of SIB 19 remains similar to that in terrestrial networks, it has some specific roles in NTN:

  • Cell Re-selection Information: SIB 19 in NTN provides critical data to user equipment (UE) about neighboring cells or satellite gateways. This information assists UEs in making decisions regarding which satellite or gateway to connect to, similar to its role in terrestrial networks.
  • Satellite or Gateway Selection: In NTN, where UEs might have multiple satellite options or gateways to choose from, SIB 19 helps UEs determine the most suitable satellite or gateway based on parameters like signal strength, quality, and other network-related information.
  • Seamless Handovers: For mobile UEs in NTN, especially those moving across different satellite beams or gateways, SIB 19 assists in seamless handovers by providing information about neighboring cells or gateways and their suitability for handover.
  • Resource Allocation: SIB 19 may also contain information related to resource allocation and management within the NTN. This data helps UEs understand the available resources and optimize their connectivity.
  • Network Efficiency: By providing UEs with accurate and up-to-date information about the network’s status and available satellites or gateways, SIB 19 contributes to the overall efficiency and performance of the NTN.
  • SIB19 contains the NTN-Config IE.
  • ta-Common
  • ta-CommonDrift
  • ta-CommonDriftVariant

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