Guest editorial IJSCN special issue on 3GPP NTN standards for future satellite communications

Abstract

WHY A NEW STANDARD FOR SATCOM? AND WHY 3RD GENERATION PARTNERSHIP PROJECT (3GPP) HAS DEVELOPED SUCH STANDARD FOR SATCOM?

With recent moves that have been seen towards the integration of satellite communication in 3GPP eco-system and the emergence of hybrid terrestrial-satellite systems, the following questions arise: What are the roles for satellite communications in 5G system? Why a new standard for Satcoms? And, why was such standard developed in 3rd Generation Partnership Project (3GPP)?

Ensuring global service continuity, high service reliability and availability are three main challenges for mobile telecommunications technologies. In Recommendation ITU-R M.2083—IMT Vision—Framework and overall objectives of the future development of IMT for 2020 and beyond, on the relationship between IMT-2020 and other access systems, it is recommended that users should be able to access services anywhere, anytime. To achieve this goal, interworking will be necessary among various access technologies, which might include a combination of different fixed, terrestrial and satellite networks. Each component should fulfill its own role, but also should be integrated or interoperable with other components to provide ubiquitous seamless coverage.

As depicted in Figure 1, prior to 3GPP Release-17, 3GPP networks are natively designed only for Terrestrial based cellular networks. On the other hand, Satellite Networks are based on proprietary technologies. Thereby, only limited interworking between Satcom based Networks and 3GPP cellular networks components is possible. 3GPP work on Non-Terrestrial Network (NTN) and the integration of satellite technology in 3GPP specifications starting from 3GPP Release-17 open a new frontier in 3GPP cellular systems and usher in new paradigms for connected society by adding a satellite component to the 5G system and thereby delivering the promise of an ubiquitous end-to-end ecosystem that can support a myriad of new use cases. Here, “integration” means that the satellite and terrestrial components of the network are able to work together seamlessly to provide coverage continuity to end users. As the 5G design is originally optimized for terrestrial network component a great care has been taken to minimize impacts at UE, NG-RAN and 5GC level while supporting the largest range of satellite network deployment scenarios.

Beyond 5G, it is expected that 6G networks will natively support both terrestrial and satellite access networks highly integrated at both service and operational level by adopting a design optimized taking into account characteristics of both network components.

Legacy Satcom systems are characterized by the reliance on industry driven technical specifications leading to proprietary architecture, protocol stack and radio access levels up to the point where basic satellite access network interoperability between different vendors is not granted. Hence the current approach followed by the Satcom industry leads to a fragmented market with vendor lock solutions able to loosely interwork with mobile systems.

In contrast, terrestrial mobile systems have benefited tremendously from international standardization efforts over the last several decades, notably in 3GPP enabling multi-vendor interoperability between the different sub-systems including but not limited to user equipment, identity module, radio access network, core network and application servers. This dynamic eco system is now addressing a global market characterized by an economy of scale hence resulting in substantial cost reduction at both CAPEX and OPEX level and a large product & service diversity for the benefits of consumer or professional end-users.

In March 2017, at RAN#75 meeting in Dubrovnik, for the first time in 3GPP, satellite industries and stakeholders have got a unique opportunity to be involved in the standardization process of a new standard integrating Terrestrial and non-Terrestrial networks. Since then, Satellite based access is included on 3GPP roadmap: as part of study items in Release-15 and Release-16 and normative work items from Release-17. The overall 3GPP journey on NTN up to Release-18 is depicted in Figure 2.

For the mobile eco-system adding a satellite components to the RAN will enrich its service offer with global service continuity and increased resilience especially towards Telecommunication User groups (Public safety, automotive, transport, drones, media and entertainment, agriculture, defense …).

Leveraging this standardization work, a number of industrial initiatives are currently being advertised. They ambition to respectively direct connectivity to smartphones or direct connectivity to IoT devices.

This special issue of the Wiley International Journal of Satellite Communications and Networking includes a set of six papers. These papers have been written by 3GPP delegates from different 3GPP working groups, with the aim of providing an insight into the 3GPP NTN specifications for future satellite communications based on 5G technology.

The first paper is an introduction to the 3GPP defined Non Terrestrial Networks standard. It provides a comprehensive view on 3GPP work on 5G New Radio to support NTN: starting from the study items in Release-15 and Release-16, and including normative works from Release-17 onward.

The second paper is about network aspects of integrating 5G and satellite communication. It discusses the recap of the 3GPP work in 3GPP Technical Specification Group Service and System Aspects (TSG SA) and 3GPP Core Network and Terminals (TSG CT).

The third paper describes the key features enabling the Radio Access Network (RAN) architecture defined for 5G to support non-terrestrial networks. To put the reader into the context, the paper provides an overview of 5G RAN and recalls the new paradigms of NTN, then introduce the NTN functionality in 5G RAN specifications with respect to feeder link switchover, cell handling, terminal registration, and Operation & Maintenance (OAM) aspects. The paper also discusses different scenarios combining satellite access with 3GPP-defined core networks.

The fourth paper is on physical layer enhancements in 5G-NR for direct access via satellite systems. It describes in details the necessary physical layer mechanism and procedure modifications for the 5G NR to support a satellite based access.

The fifth paper deals with aspects related to layer two and three. It provides an overview of the protocol adaptations to support NTNs: User plane protocol adaptations including changes to random access and Hybrid Automatic Repeat request (HARQ) to due long propagation delays. And the control plane protocol adaptations include a variety of mobility related enhancements for UEs.

The sixth paper addresses the Radio Frequency (RF) aspects of NR NTN and provides the requirements on Satellite Access Node and User Equipment for NTN in 5G New Radio as specified in 3GPP Release-17.

Last but not least, the guest editors would like to thank all individuals and organizations that made this special issue possible. All anonymous reviewers and all authors. In particular, we are grateful to Prof. Barry Evans, the Editor-in-Chief of the International Journal on Satellite Communications and Networking, for kindly inviting us to conduct this editorial process.