5G-LEO
5G-LEO – OPENAIRINTERFACE™ EXTENSION FOR 5G SATELLITE LINKS
Objectives
5G-LEO aims to accelerate the development of OAI as an open-source tool allowing the exchange and comparison of 5G NTN results by the SatCom community and facilitating the collaboration in R&D activities. The extended OAI software library is seen as an important instrument to develop early prototypes for validating key 5G NTN design aspects and providing prompt feedback to the 3GPP standardization process. The main objectives of the 5G-LEO project are the following:
- Review the reference scenarios and use cases identified for NR-NTN system deployments by 3GPP and selection of a 5G LEO baseline scenario to be implemented and verified with the extended OAI library.
- Identification of the fundamental gaps and changes needed in the code base for properly extending OAI for the 5G LEO baseline scenario.
- Implementation of the required OAI code adaptations for the different layers of the 3GPP protocol stack to support 5G LEO and closely following the developments in 3GPP standardization for 5G-NTN within Rel-17 and potentially in Rel-18.
- Set-up an end-to-end 5G LEO demonstrator in the lab for experimental validation of the OAI extension for the 5G-LEO baseline scenario.
Challenges
The key challenge of 5G-LEO is the implementation of 5G NR gNB and UE components adapted to Low Earth Orbit satellite systems while the standardization of these NTN features is still ongoing within 3GPP. More specifically, mitigating satellite RF impairments and considerable Doppler shift of the 5G signal represent specific challenges for the implementation that need to be compensated at the different layers and at the 5G NR UE and gNB.
As LEO satellites have relatively small beams and are moving fast, 3GPP currently assumes beam steering to be available on the satellite, so the 5G cell is stable on the earth while the satellite is visible. When one satellite disappears, the next satellite already provides another beam/cell on the same spot and uses a different cell ID and the UE has to perform a satellite handover. This is managed by the higher layers.
Benefits
5G-LEO helps the prototyping of and experimentation with 5G LEO communication networks closely following the 3GPP Work Item on Non-Terrestrial-Networks (NTN) and thus supporting the evolution of the 5G New Radio standard regarding NTN.
The main outcome of this activity is a publicly available new, improved version of the open source OAI software library with new features to support 5G LEO satellite communication networks. After functional and real-time validation in lab, the risks to go over live satellite links is significantly reduced.
Features
The 5G-LEO solution is characterised by the following features:
- Firstly, an important concept of 5G-LEO is to evolve an existing open-source software implementation platform, the OpenAirInterface™, which has a very considerable supporting community. This approach is expected to support achieving a significant impact;
- The main feature of the 5G-LEO platform is that it enables end-to-end testing and performance verification of 5G direct access adapted to Low Earth Orbit satellite systems using an emulator environment;
- Further important features include the mitigation of satellite RF impairments of the 5G signal as part of the implementation, in combination with the handling of considerable Doppler shift and handover rates through the compensation at the different layers of the protocol stack at the 5G NR UE and gNB.
System Architecture
The base-band processing of the OpenAirInterface (OAI) open-source software stack for gNB and UEs is performed on standard multi-core PCs, which are connected to commercial SDR transceivers, USRPs from National Instruments. On the network side the IF interface between 1 and 6 GHz is connected to the satellite-enabled channel emulator that is capable to emulate LEO satellites. On the UE side the IF interfaces are connected to the channel emulator as well. The functionalities are tested for real-time effects (timing relationships in radio layer, effects by hardware configuration, performance evaluation regarding RF effects like large Doppler shift, delay drifts etc.). The setup with gNB, UEs and 5G CN OAI is designed for later operation over real satellite links.
5G-LEO is funded by ESA under contract number 4000135152/21/NL/FGL