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5G-LEO: OPENAIRINTERFACE™ EXTENSION FOR 5G SATELLITE LINKS

Funding Source: ESA – European Space Agency

Consortium: Eurescom (Prime) Germany, Fraunhofer IIS Germany, SnT University of Luxembourg Luxembourg, AllBeSmart Portugal

Team: Prof. Symeon Chatzinotas, Dr. Jorge QUEROL, Dr. Sumit KUMAR, Dr. Oltjon KODHELI, Abdelrahman ABDALLA

Starting date / Duration: 12/2022 / 9 months

Summary

The main objective of the 5G-LEO project is to extend Openairinterface5G (OAI) software stack to support satellite systems in non-geostationary orbits. This extension will implement a full 5G protocol stack (Release ≥16) for both the UE and the gNB. The main outcome of this activity will be a publicly available new version of the open source OAI software library with new features to simulate and to test 5G LEO satellite communication links. The 5G-LEO project will speed up the development of OAI as a simulation tool that will allow the exchange and comparison of 5G NTN results by the SatCom community, facilitating the collaboration in R&D activities. It will be an important tool to develop early prototypes for validating key 5G NTN design aspects and providing prompt feedback to the 3GPP standardization process.

Project Vision

The practical experimentation with 3GPP networks has been historically reserved exclusively to network equipment vendors and telecommunication operators, primarily due to high equipment costs and licensing constraints. In recent years, the state of play has been changing with the advent of open source 3GPP software stacks based on increasingly more affordable Software Defined Radio (SDR) systems.

In this context, Openairinterface5G (OAI) has emerged as an open-source initiative that provides a reference implementation of 5G gNB, User Equipment (UE), and 5G core network (5GC) and all of them are standard compliant with 3GPP NR Release 15 and that runs on general purpose x86 computing platforms along with off-the-shelf SDR hardware platforms. OAI distinguishes itself from other similar projects through its unique open-source license, the OAI public license v1.1 , which was created by the OAI Software Alliance (OSA) in 2017. The OpenAirInterface5G code can be adapted to different use cases and deployment and new functionality can be implemented, making it an ideal platform for both industrial and academic research on 3GPP networks.

The current version of OAI implements up to 3GPP Release 15, therefore it does not support any satellite key features, which are standardized within Release 17. In order to bridge this gap, the OSA has included NTN in the OAI 5G roadmap, with a first release planned for April 2022 as shown below:

Adapting 5G to support non-terrestrial networks entails a holistic design spanning across multiple areas from radio access network to services and system aspects to core and terminals. Therefore, the changes in the OAI code base to support NTN across the full 3GPP protocol stack require a significant effort.

The 5G-LEO activity will speed up the development of OAI as simulation and emulation tool that will allow the exchange and comparison of 5G NTN results by the Satcom community, facilitating the collaboration in R&D activities. This activity will result in several important tool to develop early prototypes and demonstrators for validating key NTN design aspects in lab environment and over live satellites in parallel to the standardization process in 3GPP.

Project approach and methodology

5G-LEO project will be closely following the work in 3GPP standardization especially to the work item on NTN in release-17. Additionally, the expected follow-up activities for release-18 (potential work item starting approx. 2022) will also be considered for the developments we plan to do. The close work of 5G-LEO to 3GPP is guaranteed by the partner Fraunhofer IIS, who is actively contributing to the NT-NTN work item via several ESA projects.

As of now there are no commercial 5G equipment available for experimentations of NR-NTN, hence, our approach for implementing pre-standard extensions of 5G NR is to use existing developments based on open source 5G stack. Currently, the most promising and mature open source 5G software stack is Openairinterface5G with which the 5G-LEO partners Fraunhofer IIS, University of Luxembourg and Allbesmart have extensive experience, and are actively contributing to and promoting the platform.

Since the technology demonstrations based on pre-standard developments bear some risks, we target a three-step approach in 5G-LEO:

Non-real-time implementation of pre-standard features in 5G-LEO: In this step, we will implement selected features on different 5G radio layers and use the OAI rf-simulator to test the features (functional validation of the signal processing blocks), before going into real-time lab environment.
Real-time implementation and in-lab validations: The real-time implementation will be validated in lab with a commercial 5G channel emulator (Keysight F64) for bidirectional communication and including the capability to emulate GEO and LEO satellites. During this step, the functionality will be tested especially for real-time effects (timing relationships in radio layer, effects by hardware configuration, performance evaluation for RF effects like large Doppler offsets, delay drifts etc.).
Testing over a live satellite link: The lab-verified real-time implementation from step-2 might be used after the 5G-LEO project to go over a live, bidirectional satellite link in S-, Ku- or Ka-Band.

The figure below depicts the over system set-up for the development and testing plan (and partners) for the 5G-LEO project.