Taking the next steps on NTN and Satellite 5G

Non-terrestrial networks utilising 5G technology will soon complement terrestrial 5G systems and provide connectivity in underserved regions.

The era of commercial communications satellites began on 6 April 1965 with the launch of Intelsat 1, also known as ‘Early Bird’, into geostationary orbit (GEO). While geostationary communications satellites are ideal for providing television, radio and data broadcasting over large areas, their use for telephony services is limited due to the high latency of signals traveling over 36 000 km into space and back. Despite this obvious disadvantage, various operators have successfully offered voice and data services over GEO satellites.

In the 1990s, with the advent of terrestrial cellular communications systems, plans for global low latency telephony and data (internet) services via constellations of medium earth orbit (MEO) and low earth orbit (LEO) satellites emerged. However, early systems such as ICO, Iridium, Teledesic and Global Star failed commercially due to the extremely high costs of such mega constellations.

While many satellite operators seem to prefer ETSI/DVB satellite standards for the air interface, operators of emerging NewSpace satellite constellations and high-altitude platforms may consider using modulation and coding schemes that were developed in the context of 5G wireless communications systems.

With its Release 17, the 3GPP standardisation organisation supports 5G New Radio-based satellite access, described as non-terrestrial networks (NTN). With respect to the business-related applications, one may observe a convergence between the traditional wireless and aerospace ecosystems as both parties drive innovations further.

In 5G, non-terrestrial networks represent a plethora of connection scenarios, from satellite-based communications via airborne stations, considering connection scenarios like air-to-ground (ATG) or unmanned aerial vehicles (UAV) flight control. The holistic contemplation includes various satellite-based connectivity scenarios where the satellites differ in flying altitude, for instance GEO, MEO and LEO, and coverage area. There is also a distinction in the UE type, for instance whether it is a handheld device or a very small aperture terminal (VSAT) UE with better receiver capabilities, for example directional antennas or higher transmit power.

ATG communications provide in-flight connectivity for aircraft. Lastly, the context of NTN also considers the flight control of unmanned aerial vehicles (UAV) or unmanned aerial systems (UAS) in general.

Our understanding of 5G NTN is that it represents a technology evolution. While 3GPP Release 17 can be considered as the inception of NTN and the technology enabler in 5G systems, later releases will incorporate several enhancements and extensions, for instance the incorporation of airborne stations, so-called high-altitude platform systems (HAPS) and more onboard processing within the nodes. On the path to 6G we identify NTN as an essential part of such unified or organic networks, that will include airborne and spaceborne stations from its inception, allowing node appearance and disappearance as well as movement of network nodes relative to each other. Future network nodes will possess much higher onboard processing power, and concepts like multi-access edge computing will be incorporated in such intelligent nodes, trailblazing the path to beyond cellular.

To incorporate NTN, 3GPP launched a Release 15 study [TR 38.811] on channel models and deployment scenarios. After completing this study, 3GPP continued with a follow-up Release 16 study [TR 38.821] on solutions for adapting 5G NR to support NTN. The main objective of this study was to identify a feature set that enables NTN within the 5G system while minimising the impact on the existing 5G system.

As the major motivation to foster NTN communications we identify the request to provide ubiquitous connections all over the globe. According to several market statistics by industrial organisations such as GSMA, in 2020 wireless communications technologies covered more than 80% of the world’s population, but less than 40% of the world’s landmass. NTN satellite-based communications may tackle this aspect and focus on worldwide ubiquitous coverage in maritime, remote and polar areas.

Given RF challenges, satellite constellations and spectral circumstances such as frequency ranges or available bandwidth, we assume the first 5G NTN deployments will focus on ubiquitous connectivity and coverage. With respect to the expected data rates, NTN 5G cannot compete with terrestrial 5G, so our primary understanding is that 5G NTN will complement terrestrial 5G systems and provide connectivity in underserved regions.

*Reiner Stuhlfauth is Technology Manager (Wireless) at Rohde & Schwarz GmbH and has more than 20 years’ experience in teaching and promoting mobile communication technologies. He is involved in several projects concerning 5G, 5G advanced and 6G research.

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