Non-terrestrial networks (NTN)

Non-terrestrial networks (NTNs) are communication networks that utilizes non-ground based technologies including Satellites, UAVs, HAPs, and others through airborne or space borne technologies. These networks work together with land-based networks (such as cell and fiber optic) and are quite helpful where it is hard or even impossible to lay down the physical infrastructure.

NTN work in a space domain that encompasses satellites in LEO, MEO, and GEO, HAPs, and drones.

• LEO (Low Earth Orbit): Optimal circular orbit in such heights typ. 500-2. 000km (better delay and link budget at the cost of having to use a larger number of satellites to provide coverage).
• MEO (Medium Earth Orbit): Circular orbit in altitudes of typically. 8. 000-20. 000km
• GEO (Geostationary Earth Orbit): Apoapsis distance of 35. 786 km above the Earth’s equator (Note: Because of gravitation forces a GEO satellite is still orbiting withing a range of several kilometers as compared to the virtual and nominal position.
• HEO (Highly Elliptical Orbiting): Orbital path that is curved and slightly oval shaped moving around the earth.

Other terms used during the NTN implementations include HAPS (High-Altitude Platform Station). These are in fact UAVs that fly at very high altitudes, and often at altitudes over the surface of the earth ranging from 55,000 – 70,000 feet.

Besides, NTNs are crucial for the development of the 5G environment, and promoting international communication and network stability. They also enable more varied use across military and defense, research and private aerospace industries. In this regard, the term ‘NTN’ represents broadband data and narrow band data expansion-Internet of Things/Special Operating System (IoT-NTN/SOS), and new nonterrestrial cellular networks, which make up the majority of new advances in this field.

                                                                             Source: 3pgg.org

Nonterrestrial Networks (NTNs) differ from conventional wireless communication networks primarily in their location and coverage.  Another key difference is that NTNs can connect all mobile devices to both terrestrial and satellite networks as part of the 3GPP ecosystem unlike conventional networks where devices connected to the terrestrial network and those connected to satellite are separate.

Types of Non-Terrestrial Networks (NTNs)

1. Satellite Networks

 Satellite is a crucial aspect of NTNs because satellite is a foundational element of NTNs with widespread coverage of a diverse geography. Depending on their orbit, satellites are classified into various types, which are used for various purposes and are beneficial in different manners.

 a. Low Earth Orbit Satellites

 LEO satellite orbits are typically within 500km to 2000 km above the surface of the earth. They reconnect these computers to be conveniently adjacent to each other which allow for low latency communication ideal for real time use.

• LEO satellites provide nominal signal delay since they are nearby the Earth and such applications as internet, video conference need fast data transmission.
• LEO satellites can provide large per user data rate which is suitable for services that require high data rate. While each specific satellite has the capacity to see a comparatively limited ground area as compared to the higher orbit satellites, LEO constellations can give the benefit of global coverage through networks of many satellites.
• LEO satellites are already commonly employed to deliver relatively fast internet connection to the areas with limited connectivity. LEO networks for IoT application can be built easily to enrich machine-to-machine communication for various IoT devices and also to collect data in real-time.

 b. Medium earth orbit satellites

 MEO satellites operate in the altitude range of 2,000 km to 35, 000 km since this range provides a reasonable level of latency, extensive coverage area, and above-average data rates. MEO satellites have even better channel space utilization compared to that of LEO satellites and are more appropriate for regional usages unlike GEO satellites.

• MEO satellites are the most frequently employed in GNSS due to its height that allows offering the most precise positioning information.
• MEO satellites are the part of GPS, Galileo, and GLONASS systems that define the geographic location and time. Some of them help in the provision of broadband service and regional communications.

c. Geostationary Earth Orbit (GEO) Satellites

GEO satellites are placed mainly at 35786 kilometers above the equator and they do not move relative to a territory on Globe, and therefore provide a constant and unrestricted view over a certain region. Despite their size GEO satellites can provide coverage of a one third of the Earth’s surface and are therefore used for broadcasting and telecommunication services. The farther the satellite is from Earth the higher the latency which could be an issue for real time applications yet is appropriate for other usages.

• GEO satellites are applied for television broadcast and radio transmission because of the large coverage area. They offer long distance communication facilities for voice and data services.
• As for the GEO satellites, their main functions are to conducting observation and forecasting of meteorological condition.

 d. Highly Elliptical Orbit (HEO) Satellites

 HEO satellites have highly elliptical orbits that enable the satellites to stay for protracted durations over the desired areas especially at high latitude regions. These environments are characterized by the, high latitude locations and HEO satellites can provide extra coverage on these areas which are relatively limited by other types of satellites. These orbits help in keeping satellites’ gaze fixed on specific areas and that makes it fit for some of the broadcast and communication purpose.

• This effectively implies that the services of HEO satellites are important especially for offer communication and monitoring services in polar regions.
• Both provide broadcast services and are applicable to Surveillance & Reconnaisance.

2. High-Altitude Platforms (HAPs)

The Term High-Altitude Platforms (HAPs) forms a significant aspect of Non-Terrestrial Networks since they offer some of the special attributes in terms of communication, surveillance, and data acquisition. It works in the stratosphere usually at an altitude of between 20 km- 50 km, which enables it cover a certain region and adapt easily to numerous uses.

 Types of HAPs

 HAPs can be categorized into three main types, each offering distinct advantages and serving different purposes:HAPs can be categorized into three main types, each offering distinct advantages and serving different purposes:

 1. High-Altitude Balloons: Stratospheric balloons is a type of airborne gamma-ray telescopes that are floating light weight platforms in the stratosphere. Most are applied where only temporary or semi permanent communication is required, to gather data, or for research purposes. Depending on the message’s intended audience, the high-altitude balloons can be built to hover or travel in a specified direction, thus affording coverage within an area of interest. These platforms can be easily implemented and are not expensive which makes then ideal for emergency communication and disaster response. Thus, it can be stated that high-altitude balloons are a way to deploy broadband Internet services to the regions with little or no access to the Internet.

 2. High-Altitude Unmanned Aerial Vehicles (UAVs): High altitude UAVs are energy dependent airborne systems that can be flown at higher altitude in the stratosphere. Though they cost slightly more than balloons they are more manageable and can be used in almost every application. UAVs can stay in the sky for long durations of time; these could range from weeks to even months depending on the UAV’s make, and the type of power system used. UAV’s can be maneuvered within specific areas and redeployed as needed due to the fact that they are unmanned and can hence be commanded remotely. Military and security uses UAVs for surveillance and monitoring through receiving real-time images and videos.

3. Airships: Dirigibles or airships are floatation platforms that are used to carry large masses of weights in the stratosphere while at the same time being relatively immobile structures. These vehicles are a combination of Endurance, High Capacity Loads and Flexibility. Transmission of the airships can be fixed at one location, or maneuvered to another location depending on the coverage required. They can take sizable loads such as communication devices, monitoring instruments and research equipment and observation devices. Aerostats are employed for persistent surveillance, With the data collected, they can be used for security, environmental, and scientific purposes. They are able to function as aerial communication hubs that provide a range of services especially broadband and improve capacity of the network.

 3. Low-Altitude Platforms (LAPs)

 Low Altitude Platforms (LAPs) provide communication and have altitude at or below the stratosphere; they are at heights between 100 meters and some kilometers. They range from aerial based systems such as unmanned aerial vehicles (UAVs) and manned aircraft for localized and more flexibility modes of communication.

 Types of LAPs

 A) Unmanned aerial vehicle also referred to as drones.

 Drones are mobile and customarily quicker than all other types of platforms and can be deployed without any delay. They are more applied for communication, data gathering and acquisition and for sustaining a whole lot of specific functions. They can be rapidly mobilized hour and quickly and easily moved to areas or used for specific operations depending on need. While HAPs are aimed to provide the data for the large area, LAPs are targeted to provide the precise data in the certain area, thus they can be used in the applications with the high accuracy requirement. Drones can create communications for a short period in those areas that were devastated by disasters and the infrastructure of which was destroyed. They are applied in surveillance and security fields among different industries such as police work and structural assessment.

Some of the Patents in NTN

Hughes Network Systems, LLC

The patent EP3881632B1  aims at the issues linked to the stability of communication connections in NTNs as connected with the movement of satellites and other high-flying structures. This movement will cause frequent changes in the areas covered by the beam, and sometimes blanks, overlays and complications when choosing the beam for user equipment (UE). Concerning beam management, the patent seeks to address problems that revolve around beam switch among others, which would affect the UEs and their quality of service. The additional functionality of the proposed patent is to optimize beam, managing by changing the beam footprints according to the steering and elevating angles. It presents conditional handover configurations to enable a UE to change beam during the Call/Connection and/or after based on certain parameters such as signal strength and elevation angle. The system also enhances cell selection and reselection with the help of satellite ephemeris data and reference signal measurements for UEs to find the optimal beams. Moreover, the patent also includes ways of sending assistance information back from the UEs to the satellites to help with accurate beam control and techniques on how to regulate the beam width to guarantee proper coverage and continuity.

Samsung Electronics Co Ltd – Virtual tracking or registration areas for NTN

In Non-Terrestrial Networks, tracking and registration areas for mobile devices are challenging due to the movement of satellites and other non-terrestrial objects. The problem is that the constantly changing position of satellites leads to inefficient tracking area updates, causing increased signaling overhead and reduced performance in maintaining user connectivity​​.

The patent (US11323944B2) proposes a method for creating virtual tracking areas (VTAs) that adapt to the movement of non-terrestrial objects like satellites. By using VTAs, the system can dynamically adjust tracking areas based on satellite positions, reducing unnecessary tracking area updates and signaling. This approach ensures more efficient connectivity management and better resource utilization within NTNs​​. This method allows for seamless communication and more reliable connectivity for devices operating in NTNs, improving overall network efficiency and user experience.

Apple Inc – Routing Loops in Non-Terrestrial Networks  

Non-Terrestrial Networks (NTN) are prone to routing loops due to their highly dynamic topology and movement of satellite nodes. The continuous change in satellite positions can lead to inconsistencies in routing tables, resulting in loops that degrade network performance. This can cause delays, increase latency, and reduce the efficiency of data transmission in NTN.

The patent (US20220191898A1) proposes the use of enhanced routing protocols that incorporate real-time satellite position and trajectory data to prevent routing loops. By dynamically updating routing tables and leveraging predictive models, the system can adjust routing paths based on satellite movements. This approach minimizes routing inconsistencies, ensuring reliable and efficient communication in NTN environments.

Nokia Technologies Oy – Systems and Methods for Handover in NTN

In Non-Terrestrial Networks, handover processes are critical due to the high mobility of satellites and their frequent change in coverage areas. Traditional handover methods, primarily designed for terrestrial networks, often fail to account for the unique dynamics of NTNs. This can result in dropped connections, increased latency, and reduced service quality as devices move between different satellite footprints or transition from satellite to terrestrial networks.

The patent (US20200077358A1) proposes optimized handover techniques tailored for NTN environments. It utilizes predictive algorithms to anticipate satellite movements and proactively manage handover processes. By incorporating satellite trajectory data and network conditions, the system can determine the optimal time and strategy for handovers. This approach minimizes connection drops, ensures seamless transitions between satellites and terrestrial networks, and enhances the overall reliability and performance of NTN communication systems.